Murmansk State Technical University

Department of Biology

Report on the topic:

"Research methods in cytology"

Completed:

1st year student

Faculty of Technology

Departments Biology

Serebryakova Lada Vyacheslavovna

Checked:

Murmansk 2001

Plan:

1. What does cytology study?

2. The idea that organisms are made of cells.

3. Research methods used in cytology.

4. Cell fractionation.

5. Autoradiography.

6. Determination of the duration of some stages of the cell cycle using autoradiography.

Cytology is the science of cells. It emerged from other biological sciences almost 100 years ago. For the first time, generalized information about the structure of cells was collected in a book by J.-B. Carnoy's Biology of the Cell, published in 1884. Modern cytology studies the structure of cells, their functioning as elementary living systems: the functions of individual cellular components, the processes of cell reproduction, their repair, adaptation to environmental conditions and many other processes are studied, allowing one to judge the properties and functions common to all cells. Cytology also examines the structural features of specialized cells. In other words, modern cytology is the physiology of the cell. Cytology is closely associated with scientific and methodological achievements of biochemistry, biophysics, molecular biology and genetics. This served as the basis for an in-depth study of the cell from the standpoint of these sciences and the emergence of a certain synthetic science about the cell - cell biology, or cell biology. Currently, the terms cytology and cell biology coincide, since their subject of study is the cell with its own patterns of organization and functioning. The discipline “Cell Biology” refers to the fundamental sections of biology, because it studies and describes the only unit of all life on Earth – the cell.

A long and careful study of the cell as such led to the formulation of an important theoretical generalization that has general biological significance, namely the emergence of the cell theory. INXVIIV. Robert Hooke, a physicist and biologist, distinguished by great ingenuity, created a microscope. Examining a thin section of cork under his microscope, Hooke discovered that it was built from tiny empty cells separated by thin walls, which, as we now know, consist of cellulose. He called these small cells cells. Later, when other biologists began to examine plant tissues under a microscope, it turned out that the small cells discovered by Hooke in a dead, withered plug were also present in living plant tissues, but they were not empty, but each contained a small gelatinous body. After animal tissues were subjected to microscopic examination, it was found that they also consisted of small gelatinous bodies, but that these bodies were only rarely separated from each other by walls. As a result of all these studies, in 1939, Schleiden and Schwann independently formulated the cell theory, which states that cells are the elementary units from which all plants and all animals are ultimately built. For some time, the double meaning of the word cell still caused some misunderstandings, but then it became firmly established in these small jelly-like bodies.

The modern understanding of the cell is closely related to technical advances and improvements in research methods. In addition to conventional light microscopy, which has not lost its role, polarization, ultraviolet, fluorescence, and phase contrast microscopy have gained great importance in the last few decades. Among them, electron microscopy occupies a special place, the resolution of which made it possible to penetrate and study the submicroscopic and molecular structure of the cell. Modern research methods have made it possible to reveal a detailed picture of cellular organization.

Each cell consists of a nucleus and cytoplasm, separated from each other and from the external environment by membranes. The components of the cytoplasm are: membrane, hyaloplasm, endoplasmic reticulum and ribosomes, Golgi apparatus, lysosomes, mitochondria, inclusions, cell center, specialized organelles.

A part of an organism that performs a special function is called an organ. Any organ - lung, liver, kidney, for example - each has its own special structure, thanks to which it plays a certain role in the body. In the same way, there are special structures in the cytoplasm, the peculiar structure of which gives them the opportunity to carry out certain functions necessary for the metabolism of the cell; these structures are called organelles (“little organs”).

Elucidation of the nature, function and distribution of cytoplasmic organelles became possible only after the development of methods of modern cell biology. The most useful in this regard were: 1) electron microscopy; 2) cell fractionation, with the help of which biochemists can isolate relatively pure fractions of cells containing certain organelles, and thus study individual metabolic reactions of interest to them; 3) autoradiography, which made it possible to directly study individual metabolic reactions occurring in organelles.

The method by which organelles are isolated from cells is called fractionation. This method turned out to be very fruitful, giving biochemists the opportunity to isolate various cell organelles in a relatively pure form. It also allows one to determine the chemical composition of organelles and the enzymes they contain and, based on the data obtained, to draw conclusions about their functions in the cell. As a first step, the cells are destroyed by homogenization in some suitable medium that preserves the organelles and prevents their aggregation. Very often a sucrose solution is used for this. Although mitochondria and many other cellular organelles remain intact, membrane structures such as the endoplasmic reticulum and the plasma membrane disintegrate into fragments. However, the resulting membrane fragments often close on themselves, resulting in round vesicles of various sizes.

At the next stage, the cell homogenate is subjected to a series of centrifugations, the speed and duration of which increases each time; this process is called differential centrifugation. Different cell organelles are deposited at the bottom of centrifuge tubes at different centrifugation speeds, which depends on the size, density and shape of the organelles. The resulting precipitate can be collected and examined. Larger, denser structures such as nuclei are the fastest to settle, while smaller, less dense structures such as endoplasmic reticulum vesicles require higher rates and longer times to settle. Therefore, at low centrifugation speeds, the nuclei are sedimented, while other cellular organelles remain in suspension. At higher speeds, mitochondria and lysosomes precipitate, and with prolonged centrifugation and very high speeds, even small particles such as ribosomes precipitate. Precipitates can be examined using an electron microscope to determine the purity of the resulting fractions. All fractions are contaminated to some extent with other organelles. If, nevertheless, it is possible to achieve sufficient purity of the fractions, they are then subjected to biochemical analysis to determine the chemical composition and enzymatic activity of the isolated organelles.

More recently, another method of cell fractionation was created - density gradient centrifugation; In this case, centrifugation is carried out in a test tube in which sucrose solutions of increasing concentrations and, consequently, increasing density are first layered on top of each other. During centrifugation, the organelles contained in the homogenate are located in a centrifuge tube at the same levels as sucrose solutions corresponding to them in density. This method gives biochemists the ability to separate organelles of the same size but different densities (Fig. 1.).

Autoradiography is a relatively new method that has immensely expanded the capabilities of both light and electron microscopy. This is a highly modern method, owing its origin to the development of nuclear physics, which made it possible to obtain radioactive isotopes of various elements. Autoradiography requires, in particular, isotopes of those elements that are used by the cell or can bind to substances used by the cell, and that can be administered to animals or added to cultures in quantities that do not disrupt normal cellular metabolism. Because a radioactive isotope (or the substance labeled with it) participates in biochemical reactions in the same way as its non-radioactive counterpart and at the same time emits radiation, the path of isotopes in the body can be traced using various methods of detecting radioactivity. One way to detect radioactivity is based on its ability to act like light on photographic film; but the radioactive radiation penetrates the black paper used to protect the film from light and has the same effect on the film as light.

So that the radiation emitted by radioactive isotopes can be detected on preparations intended for study using light or electron microscopes, the preparations are coated in a dark room with a special photographic emulsion, and then left for some time in the dark. Then the preparations are developed (also in the dark) and fixed. Areas of the drug containing radioactive isotopes affect the underlying emulsion, in which dark “grains” appear under the influence of the emitted radiation. Thus, radioautographs are obtained (from the Greek.radio – radiate,autos – himself andgrapho - write).

At first, histologists had only a few radioactive isotopes; for example, many early autoradiography studies used radioactive phosphorus. Later, much more of these isotopes began to be used; The radioactive isotope of hydrogen, tritium, has found particularly widespread use.

Autoradiography was and still is very widely used to study where and how certain biochemical reactions occur in the body.

Chemical compounds labeled with radioactive isotopes that are used to study biological processes are called precursors. Precursors are usually substances similar to those the body obtains from food; they serve as building blocks for tissue construction and are incorporated into complex components of cells and tissues in the same way that unlabeled building blocks are incorporated into them. The tissue component into which the labeled precursor is incorporated and which emits radiation is called the product.

Cells grown in culture, although belonging to the same type, will be at different stages of the cell cycle at any given time unless special measures are taken to synchronize their cycles. However, by introducing tritium-thymidine into cells and then making autoradiographs, the duration of the various stages of the cycle can be determined. The time of onset of one stage - mitosis - can be determined without labeled thymidine. To do this, a sample of cells from the culture is kept under observation in a phase-contrast microscope, which makes it possible to directly monitor the progress of mitosis and determine its timing. The duration of mitosis is usually 1 hour, although in some types of cells it takes up to 1.5 hours.

G 2-period .

To determine the duration of the G 2 period, a method known aspulse tag: Labeled thymidine is added to the cell culture, and after a short time the culture medium is replaced with fresh one in order to prevent further uptake of labeled thymidine by the cells. In this case, the label is included only in those cells that, during a short stay in a medium with tritium-thymidine, were inS-period of the cell cycle. The proportion of such cells is small and only a small part of the cells will receive the label. In addition, all cells that include the label will be in interphase - from cells that have barely enteredS-period, to those that almost ended it during exposure to tritium-thymidine. In a sample taken immediately after removal of labeled thymidine, the label is contained only in interphase nuclei belonging to cells that were inS-period; the same cells that were in a state of mitosis during this period remain unlabeled.

If you then continue to take samples from the culture at certain intervals and make an autoradiograph for each successive sample, then a moment will come when the label begins to appear inmitotic d -chromosomes . Labels will be included in all those cells that were in the presence of tritium-thymidine in the medium.S-period, and among these cells there will be those who have just enteredS-period, and almost ended it. It is quite obvious that these latter will be the first among the labeled cells to undergo mitosis and, therefore, the label will be detected in their mitotic chromosomes. Thus, the interval between 1) the time when labeled thymidine was removed from the culture and 2) the time of appearance of labeled mitotic chromosomes will correspond to the durationG2 periods of the cell cycle.

Determining Duration S -period .

Since the cells that are at the very end when the label is introduced into the mediumS-period will be the first to enter mitosis, then, consequently, in those cells in whichS-the period begins immediately before the label is removed; labeled mitotic chromosomes will appear last. Therefore, if we could determine the interval between the time of entry into mitosis of the cells marked first and the cells marked last, we would establish the durationS-period. However, although the time when labeled mitotic chromosomes first appear is easy to determine, the time at which the last labeled cells enter mitosis cannot be determined (this is hampered by the very large number of labeled dividing cells in the latter samples). Therefore the durationS-periods have to be determined in a different way.

When examining autoradiographs of successive samples of cells taken at regular intervals, it is discovered that the proportion of cells carrying the label in their mitotic chromosomes gradually increases until literally all dividing cells are labeled. However, as the cells complete mitosis one by one, they become labeled interphase cells. The first to complete mitosis are those of the labeled cells that entered it first; and accordingly, of the cells with labeled mitotic chromosomes, the last to complete mitosis are those that entered it later than all. Since the duration of mitosis is always the same, then, therefore, if we could determine the interval between: 1) the time of the end of mitosis in the cells that turned on the mark first, and 2) the time of the end of mitosis in the cells that turned on the mark last, we would establish the durationS-period. DurationS-period can be easily established by determining the interval between: 1) the point in time when 50% of the mitotic cells in the culture carry the label, and 2) the point in time after which the culture no longer contains 50% of the labeled cells.

Determination of generation time (total duration of the entire cell cycle).

Continuing to take cell samples from the culture, you can find that the marked mitotic figures completely disappear at some point, and then appear again. Such dividing cells are daughter cells derived from those mother cells that turned on the label while being exposed to tritium-thymidineS-period. These mother cells passed intoS-period, divided, and then went through a second interphase and a second division, that is, they went through one full cycle and part of the next. The time required to complete a complete cell cycle is called timegeneration. It corresponds to the interval between two successive peaks of label incorporation and usually corresponds to the segment between those points of successive ascending curves at which 50% of the mitotic figures contain the label.

Literature.

A. Ham, D. Cormack “Histology”, volume 1 Moscow “MIR” 1982;

M.G. Abramov “Clinical Cytology” Moscow “MEDICINE” 1974;

Y.S.Chentsov “General cytology”

Basics of cytology

Cell. Cell theory.

Cell- the smallest structure capable of self-reproduction. The term “cell” was introduced by R. Hooke in 1665 (he studied with a microscope a section of an elderberry stem - the core and plug; although Hooke himself saw not cells, but their membranes). Improvements in microscopic technology have made it possible to identify the diversity of cell shapes, the complexity of the structure of the nucleus, the process of cell division, etc. The microscope was improved by Anthony van Leeuwenhoek (his microscopes provided a magnification of 270-300 times).

Other cell research methods:

1. differential centrifugation- based on the fact that different cellular structures have different densities. With very rapid rotation in the device (ultracentrifuge), the organelles of finely ground cells precipitate out of the solution, arranged in layers in accordance with their density. These layers are separated and studied.
2. electron microscopy- used since the 30s of the 20th century (when the electron microscope was invented - it provides magnification up to 10 6 times); Using this method, the structure of the smallest cell structures is studied, incl. individual organelles and membranes.
3. autoradiography- a method that allows you to analyze the localization in cells of substances labeled with radioactive isotopes. This is how the sites of synthesis of substances, the composition of proteins, and intracellular transport pathways are revealed.
4. phase contrast microscopy- used to study transparent, colorless objects (living cells). When passing through such a medium, light waves are shifted by an amount determined by the thickness of the material and the speed of light passing through it. A phase contrast microscope converts these shifts into a black and white image.
5. X-ray diffraction analysis- studying cells using X-rays.

In 1838-1839 was created by botanist Matthias Schleiden and physiologist Theodor Schwann cell theory. Its essence was that the main structural element of all living organisms (plants and animals) is the cell.

Basic principles of cell theory:

1. cell - an elementary living system; the basis of the structure, life activity, reproduction and individual development of organisms.
2. cells of various tissues of the body and cells of all organisms are similar in structure and chemical composition.
3. new cells arise only by dividing pre-existing cells.
4. the growth and development of any multicellular organism is a consequence of the growth and reproduction of one or more original cells.

Molecular composition of the cell.

Chemical elements that make up cells and perform certain functions are called biogenic. According to the content, the elements that make up the cell are divided into three groups:

1. macronutrients- make up the bulk of the cell - 99%. Of these, 98% are accounted for by 4 elements: C, O, H and N. This group also includes K, Mg, Ca, P, C1, S, Na, Fe.
2. microelements- These include mainly ions that are part of enzymes, hormones and other substances. Their concentration is from 0.001 to 0.000001% (B, Cu, Zn. Br, I, Mo, etc.).
3. ultramicroelements- their concentration does not exceed 10 -6%, and their physiological role has not been identified (Au, Ag, U, Ra).

The chemical components of living things are divided into inorganic(water, mineral salts) and organic(proteins, carbohydrates, lipids, nucleic acids, vitamins).

Water. With a few exceptions (bone and tooth enamel), water is the predominant component of cells - on average 75-85%. In a cell, water is in a free and bound state. A water molecule is dipole- there is a negative charge at one end and a positive charge at the other, but overall the molecule is electrically neutral. Water has a high heat capacity and relatively high thermal conductivity for liquids.

Biological significance of water: universal solvent (for polar substances, non-polar substances do not dissolve in water); environment for reactions, participant in reactions (protein breakdown), participates in maintaining the thermal equilibrium of the cell; source of oxygen and hydrogen during photosynthesis; the main means of transport of substances in the body.

Ions and salts. Salts are part of bones, shells, shells, etc., i.e. perform supporting and protective functions, and also participate in mineral metabolism. Ions are part of various substances (iron - hemoglobin, chlorine - hydrochloric acid in the stomach, magnesium - chlorophyll) and participate in regulatory and other processes, as well as in maintaining homeostasis.

Squirrels. In terms of content in the cell, they occupy first place among organic substances. Proteins are irregular polymers made up of amino acids. Proteins contain 20 different amino acids. Amino acid:

NH 2 -CH-COOH | R

The joining of amino acids occurs as follows: the amino group of one acid combines with the carboxyl group of another, and a water molecule is released. The resulting bond is called peptide(a type of covalent), and the compound itself is peptide. A compound of a large number of amino acids is called polypeptide. If a protein consists only of amino acids, then it is called simple ( protein), if it contains other substances, then complex ( proteid).

The spatial organization of proteins includes 4 structures:

1. Primary(linear) - polypeptide chain, i.e. a string of amino acids linked by covalent bonds.
2. Secondary- the protein thread twists into a spiral. Hydrogen bonds arise in it.
3. Tertiary- the spiral further coagulates, forming a globule (ball) or fibril (elongated structure). Hydrophobic and electrostatic interactions occur in it, as well as covalent disulfide -S-S- bonds.
4. Quaternary- joining several protein macromolecules together.

The destruction of protein structure is called denaturation. It can be irreversible (if the primary structure is damaged) or reversible (if other structures are damaged).

Functions of proteins:

1. enzymes- These are biologically active substances; they catalyze chemical reactions. More than 2000 enzymes are known. Properties of enzymes: specificity of action (each acts only on a certain substance - substrate), activity only in a certain environment (each enzyme has its own optimal pH range) and at a certain temperature (with increasing temperature the probability of denaturation increases, so enzyme activity decreases), greater efficiency actions with little content. Any enzyme has active center- this is a special site in the structure of the enzyme to which a substrate molecule is attached. Currently, based on their structure, enzymes are divided into two main groups: completely protein enzymes and enzymes consisting of two parts: apoenzyme (protein part) and coenzyme (non-protein part; this is an ion or molecule that binds to the protein part, thereby forming a catalytically active complex). Coenzymes are metal ions and vitamins. Without the coenzyme, the apoenzyme does not function.
2. regulatory - hormones.
3. transport - hemoglobin.
4. protective - immunoglobulins (antibodies).
5. movement - actin, myosin.
6. construction (structural).
7. energy - extremely rarely, only after carbohydrates and lipids have run out.

Carbohydrates- organic substances, which include C, O and H. General formula: C n (H 2 O) n, where n is at least 3. They are divided into 3 classes: monosaccharides, disaccharides (oligosaccharides) and polysaccharides.

Monosaccharides(simple carbohydrates) - consist of one molecule, these are solid crystalline substances, highly soluble in water, having a sweet taste. Ribose And deoxyribose(C 5) - are part of DNA and RNA. Glucose(C 6 H 12 O 6) - part of polysaccharides; the main primary source of energy in the cell. Fructose And galactose- glucose isomers.

Oligosaccharides- consist of 2, 3 or 4 monosaccharide residues. Most important disaccharides- they consist of 2 residues; highly soluble in water, sweet in taste. Sucrose(C 12 H 22 O 11) - consists of glucose and fructose residues; widely distributed in plants. Lactose (milk sugar)- consists of glucose and galactose. The most important source of energy for young mammals. Maltose- consists of 2 glucose molecules. It is the main structural element of starch and glycogen.

Polysaccharides- high molecular weight substances consisting of a large number of monosaccharide residues. They are poorly soluble in water and do not have a sweet taste. Starch- is presented in two forms: amylose (consists of glucose residues connected in an unbranched chain) and amylopectin (consists of glucose residues, linear and branched chains). Glycogen- polysaccharide of animals and fungi. The structure resembles starch, but is more branched. Fiber (cellulose)- the main structural polysaccharide of plants, part of cell walls. This is a linear polymer.

Functions of carbohydrates:

1. energy - 1 g at complete breakdown gives 17.6 kJ.
2. Structural.
3. Supporting (in plants).
4. Supply of nutrients (starch and glycogen).
5. Protective - viscous secretions (mucus) are rich in carbohydrates and protect the walls of hollow organs.

Lipids- combine fats and fat-like substances - lipoids. Fats- These are esters of fatty acids and glycerol. Fatty acids: palmitic, stearic (saturated), oleic (unsaturated). Vegetable fats are rich in unsaturated acids, so they are fusible and liquid at room temperature. Animal fats contain mainly saturated acids, so they are more refractory and solid at room temperature. All fats are insoluble in water, but dissolve well in non-polar solvents; conduct heat poorly. Fats include phospholipids(this is the main component of cell membranes) - they contain a phosphoric acid residue. Lipoids include steroids, waxes, etc.

Functions of lipids:

1. structural
2. energy - 1 g at complete breakdown gives 38.9 kJ.
3. Nutrient storage (adipose tissue)
4. Thermoregulation (subcutaneous fat)
5. Suppliers of endogenous water - when 100 g of fat is oxidized, 107 ml of water is released (camel principle)
6. Protecting internal organs from damage
7. Hormones (estrogens, androgens, steroid hormones)
8. Prostaglandins are regulatory substances that maintain vascular and smooth muscle tone and participate in immune reactions.

ATP (adenosine triphosphoric acid). The energy released during the breakdown of organic substances is not immediately used for work in cells, but is first stored in the form of a high-energy compound - ATP. ATP consists of three phosphoric acid residues, ribose (a monosaccharide) and adenine (a nitrogenous base residue). When one phosphoric acid residue is eliminated, ADP is formed, and if two residues are eliminated, AMP is formed. The elimination reaction of each residue is accompanied by the release of 419 kJ/mol. This phosphorus-oxygen bond in ATP is called macroergic. ATP has two high-energy bonds. ATP is formed in mitochondria from AMP, which attaches first one, then the second phosphoric acid residue with the absorption of 419 kJ/mol of energy (or from ADP with the addition of one phosphoric acid residue).

Examples of processes that require large amounts of energy: protein biosynthesis.

Nucleic acids- These are high-molecular organic compounds that ensure the storage and transmission of hereditary information. First described in the 19th century (1869) by the Swiss Friedrich Miescher. There are two types of nucleic acids.

DNA (deoxyribonucleic acid)

Cage maintenance is strictly constant. It is mainly found in the nucleus (where it forms chromosomes, consisting of DNA and two types of proteins). DNA is an irregular biopolymer, the monomer of which is a nucleotide consisting of a nitrogenous base, a phosphoric acid residue and a deoxyribose monosaccharide. There are 4 types of nucleotides in DNA: A (adenine), T (thymine), G (guanine) and C (cytosine). A and G belong to purine bases, C and T to pyrimidine bases. Moreover, in DNA the number of purine bases is equal to the number of pyrimidine bases, as well as A=T and C=G (Chargaff’s rule).

In 1953, J. Watson and F. Crick discovered that the DNA molecule is a double helix. Each helix consists of a polynucleotide chain; the chains are twisted one around the other and together around a common axis, each turn of the helix contains 10 pairs of nucleotides. The chains are held together by hydrogen bonds that arise between the bases (two bonds between A and T, three bonds between C and G). Polynucleotide chains are complementary to each other: opposite adenine in one chain there is always thymine of the other and vice versa (A-T and T-A); opposite cytosine is guanine (C-G and G-C). This principle of DNA structure is called the principle of addition or complementarity.

Each DNA strand has a specific orientation. The two strands in a DNA molecule are located in opposite directions, i.e. antiparallel.

The main function of DNA is the storage and transmission of hereditary information.

RNA (ribonucleic acid)

1. i-RNA (messenger RNA) - found in the nucleus and cytoplasm. Its function is to transfer information about the structure of the protein from DNA to the site of protein synthesis.
2. t-RNA (transfer RNA) - mainly in the cytoplasm of the cell. Function: transfer of amino acid molecules to the site of protein synthesis. This is the smallest RNA.
3. r-RNA (ribosomal RNA) - participates in the formation of ribosomes. This is the largest RNA.

Cell structure.

The main components of a cell are: the outer cell membrane, cytoplasm and nucleus.

Membrane. The composition of the biological membrane ( plasma membranes) includes lipids that form the basis of the membrane and high molecular weight proteins. Lipid molecules are polar and consist of charge-bearing polar hydrophilic heads and non-polar hydrophobic tails (fatty acids). The membrane mainly contains phospholipids(they contain a phosphoric acid residue). Membrane proteins can be superficial, integral(pierce the membrane right through) and semi-integral(immersed in membrane).

The modern model of a biological membrane is called “universal liquid mosaic model”, according to which globular proteins are immersed in a lipid bilayer, with some proteins penetrating it through, others partially. It is believed that integral proteins are amphiphilic, their nonpolar regions are immersed in a lipid bilayer, and their polar regions protrude outward, forming a hydrophilic surface.

Submembrane system of the cell (submembrane complex). It is a specialized peripheral part of the cytoplasm and occupies a border position between the working metabolic apparatus of the cell and the plasma membrane. In the submembrane system of the surface apparatus, two parts can be distinguished: peripheral hyaloplasm, where enzymatic systems associated with the processes of transmembrane transport and reception are concentrated, and structurally formed musculoskeletal system. The supporting contractile system consists of microfibrils, microtubules and skeletal fibrillar structures.

Supramembrane structures Eukaryotic cells can be divided into two broad categories.

1. The supramembrane complex proper, or glycocalyx thickness 10-20 nm. It consists of peripheral membrane proteins, carbohydrate parts of glycolipids and glycoproteins. The glycocalyx plays an important role in receptor function and ensures “individualization” of the cell - it contains histocompatibility receptors.
2. Derivatives of supramembrane structures. These include specific chemical compounds that are not produced by the cell itself. They have been most studied on the microvilli of mammalian intestinal epithelial cells. Here they are hydrolytic enzymes adsorbed from the intestinal cavity. Their transition from a suspended to a fixed state creates the basis for a qualitatively different type of digestion, the so-called parietal digestion. The latter inherently occupies an intermediate position between cavity and intracellular.

Functions of biological membrane:

1. barrier;
2. receptor;
3. cell interaction;
4. maintaining cell shape;
5. enzymatic activity;
6. transport of substances into and out of the cell.

Membrane transport:

1. For micromolecules. There are active and passive transport.

   TO passive include osmosis, diffusion, filtration. Diffusion- transport of a substance towards a lower concentration. Osmosis- movement of water towards a solution with higher concentration. Water and fat-soluble substances move with the help of passive transport.

   TO active Transport includes: transfer of substances with the participation of carrier enzymes and ion pumps. The carrier enzyme binds the transported substance and “drags” it into the cell. The ion pump mechanism is discussed using an example of operation potassium-sodium pump: during its operation, three Na+ are transferred from the cell for every two K+ into the cell. The pump operates on the principle of opening and closing channels and, by its chemical nature, is an enzyme protein (breaks down ATP). The protein binds to sodium ions, changes its shape, and a channel is formed inside it for the passage of sodium ions. After these ions pass through, the protein changes shape again and a channel opens through which potassium ions flow. All processes are energy dependent.

   The fundamental difference between active and passive transport is that it requires energy, while passive transport does not.

2. For macromolecules. Occurs through the active capture of substances by the cell membrane: phagocytosis and pinocytosis. Phagocytosis- capture and absorption of large particles by the cell (for example, destruction of pathogenic microorganisms by macrophages of the human body). First described by I.I. Mechnikov. Pinocytosis- the process of capture and absorption by a cell of drops of liquid with substances dissolved in it. Both processes occur according to a similar principle: on the surface of the cell, the substance is surrounded by a membrane in the form of a vacuole, which moves inward. Both processes involve energy consumption.

Cytoplasm. In the cytoplasm, there is a main substance (hyaloplasm, matrix), organelles (organelles) and inclusions.

Main substance fills the space between the plasmalemma, nuclear envelope and other intracellular structures. It forms the internal environment of the cell, which unites all intracellular structures and ensures their interaction with each other. Cytoplasm behaves like a colloid, capable of transitioning from a gel to a sol state and back. Sol is a state of matter characterized by low viscosity and devoid of cross-links between microfilaments. Gel is a state of matter characterized by high viscosity and the presence of bonds between microfilaments. The outer layer of cytoplasm, or ectoplasm, has a higher density and is devoid of granules. Examples of processes occurring in the matrix: glycolysis, the breakdown of substances to monomers.

Organelles- cytoplasmic structures that perform specific functions in the cell.

Organelles are:

1. membrane (single- and double-membrane (mitochondria and plastids)) and non-membrane.
2. organelles of general importance and special ones. The first include: ER, Golgi apparatus, mitochondria, ribosomes and polysomes, lysosomes, cell center, microbodies, microtubules, microfilaments. Organelles for special purposes (present in cells that perform specialized functions): cilia and flagella (cell movement), microvilli, synaptic vesicles, myofibrils.

organoid	structure	functions
membrane
EPS	a system of interconnected tubules and cavities of various shapes and sizes. Forms a continuous structure with the nuclear membrane. There are two types: smooth and granular or rough (there are ribosomes on it)	synthesis and intracellular transport of proteins (rough); synthesis and breakdown of lipids and carbohydrates (smooth)
Golgi apparatus (lamellar complex)	consists of cavities arranged in a stack. Bubbles may form at the ends of the cavities and separate from them	sorting and packaging of macromolecules, transport of substances, participation in the formation of lysosomes
Lysosomes	these are vesicles with a diameter of 5 microns containing hydrolytic enzymes	breakdown of organic substances, old cell parts, whole cells and even individual organs (tadpole tail)
Vacuole	only in plants (up to 90% of the cell volume). Large cavity in the center of the cell filled with cell sap	reservoir of water and substances dissolved in it, color, internal (turgor) pressure of the cell
Mitochondria	rod-shaped, thread-like or spherical organelles with a double membrane - an outer smooth one and an inner one with numerous projections (cristae). There is space between the membranes. Enzymes are located on the inner membrane. Inside is a substance called the matrix, containing DNA, RNA and mitochondrial ribosomes	participate in cell energy metabolism
Plastids	only in plants. Leukoplasts (colorless) are common in plant organs that are hidden from sunlight. Chloroplasts (green) have two membranes and a matrix inside. The internal membrane is well developed, having folds, between which there are vesicles - thylakoids. Some thylakoids are collected like a stack into groups called grana. Chromoplasts (yellow-orange) are found in colored organs - petals, fruits, roots and autumn leaves. There is usually no inner membrane	photosynthesis, coloring, supply of substances
non-membrane
cell center	found in animals and lower plants; absent in higher plants. Consists of 2 centrioles and microtubules	organization of the cell cytoskeleton; participation in cell division (forms a spindle)
ribosomes and polysomes	these are spherical structures. They consist of 2 subunits - large and small. Contain r-RNA. Found on the ER or freely in the cytoplasm. A polysome is a structure consisting of one mRNA and several ribosomes located on it.	protein synthesis
musculoskeletal system	forms the cytoskeleton of the cell. It includes microbodies, microtubules, microfilaments. Microfilaments consist of globular actin protein molecules. Microtubules are hollow protein cylinders found in the cilium or flagellum.	determine the shape of cells, participate in cell movement, support function

Cellular inclusions- these are non-permanent formations, either appearing or disappearing during the life of the cell, i.e. These are products of cellular metabolism. Most often they are found in the cytoplasm, less often in organelles or in the nucleus. Inclusions are represented mainly by granules (polysaccharides: glycogen in animals, starch in plants; less commonly, proteins in the cytoplasm of eggs), droplets (lipids) and crystals (calcium oxalate). Cellular inclusions also include some pigments - yellow and brown lipofuscin (accumulates during cell aging), retinin (part of the visual pigment), hemoglobin, melanin, etc.

Core. The main function of the nucleus is to store hereditary information. The components of the nucleus are the nuclear envelope, nucleoplasm (nuclear juice), nucleolus (one or two), chromatin clumps (chromosomes). The nuclear envelope of a eukaryotic cell separates the hereditary material (chromosomes) from the cytoplasm, in which a variety of metabolic reactions take place. The nuclear envelope consists of 2 biological membranes. At certain intervals, both membranes merge with each other, forming pores- These are holes in the nuclear membrane. Through them, exchange of substances with the cytoplasm occurs.

The basis nucleoplasm made up of proteins, including fibrillar ones. It contains enzymes necessary for the synthesis of nucleic acids and ribosomes. Nuclear sap also contains RNA.

Nucleoli- this is the site of ribosome assembly; these are unstable nuclear structures. They disappear at the beginning of cell division and reappear towards the end. The nucleolus is divided into an amorphous part and a nucleolar filament. Both components are built from filaments and granules, consisting of proteins and RNA.

Chromosomes. Chromosomes consist of DNA, which is surrounded by two types of proteins: histone(main) and non-histone(sour). Chromosomes can be in two structural and functional states: spiralized And despiralized. The partially or completely decondensed (despiralized) state is called working, because in this state, the processes of transcription and reduplication occur. Inactive state - in a state of metabolic rest at their maximum condensation, when they perform the function of distributing and transferring genetic material to daughter cells.

IN interphase chromosomes are represented by a ball of thin threads, which are visible only under an electron microscope. During division, chromosomes shorten and thicken, they are spiralized and clearly visible under a microscope (best at the metaphase stage). At this time, chromosomes consist of two chromatids connected by a primary constriction, which divides each chromatid into two sections - arms.

Based on the location of the primary constriction, several types of chromosomes are distinguished:

1. metacentric or equal arms (both arms of the chromosome have the same length);
2. submetacentric or unequal arms (the arms of the chromosome are slightly different in size);
3. acrocentric(one shoulder is very short).

Cell metabolism.

This is one of the main properties of living things. Metabolism is possible due to the fact that living organisms are open systems, i.e. There is a constant exchange of substances and energy between the body and the environment. Metabolism occurs in all organs, tissues and cells, ensuring self-renewal of morphological structures and the chemical composition of the cytoplasm.

Metabolism consists of two processes: assimilation (or plastic exchange) and dissimilation (or energy exchange). Assimilation(plastic metabolism) - the totality of all biosynthesis processes taking place in living organisms. Dissimilation(energy metabolism) - the totality of all processes of decomposition of complex substances into simple ones with the release of energy, taking place in living organisms.

According to the method of assimilation and depending on the type of energy used and starting substances, organisms are divided into autotrophs (photosynthetics and chemosynthetics) and heterotrophs. Autotrophs- these are organisms that independently synthesize organic substances using the energy of the Sun ( photoautotrophs) or the energy of oxidation of inorganic substances ( chemoautotrophs). Autotrophs include plants, bacteria, and blue-green ones. Heterotrophs- these are organisms that receive ready-made organic substances along with food. These include animals, fungi, bacteria.

The role of autotrophs in the cycle of substances is enormous: 1) they transform the energy of the Sun into the energy of chemical bonds of organic substances, which is used by all other living beings on our planet; 2) saturate the atmosphere with oxygen (photoautotrophs), which is necessary for most heterotrophs to obtain energy by oxidizing organic substances. Heterotrophs also play an important role in the cycle of substances: they secrete inorganic substances (carbon dioxide and water) used by autotrophs.

Dissimilation. All heterotrophic organisms obtain energy as a result of redox reactions, i.e. those in which electrons are transferred from electron donors - reducing agents to electron acceptors - oxidizing agents.

Energy metabolism aerobic organisms consists of three stages:

1. preparatory, which passes in the gastrointestinal tract or in the cell under the action of lysosome enzymes. During this stage, all biopolymers decompose into monomers: proteins decompose first into peptides, then into amino acids; fats - to glycerol and fatty acids; carbohydrates - to monosaccharides (to glucose and its isomers).
2. oxygen-free(or anaerobic), which takes place in the cytoplasmic matrix. This stage is called glycolysis. Under the action of enzymes, glucose is broken down into two PVC molecules. In this case, 4 H atoms are released, which are accepted by a substance called NAD + (nicotinamide adenine dinucleotide). In this case, NAD + is restored to NAD*H (this stored energy will later be used for the synthesis of ATP). Also, due to the breakdown of glucose, 4 ATP molecules are formed from ADP. In this case, 2 ATP molecules are consumed during the chemical reactions of glycolysis, so the total ATP yield after glycolysis is 2 ATP molecules.
3. oxygen, which takes place in the mitochondria. Two PVA molecules enter an enzymatic ring “conveyor” called the Krebs cycle or tricarboxylic acid cycle. All enzymes in this cycle are located in mitochondria.

Once in the mitochondria, PVC is oxidized and converted into an energy-rich substance - acetyl coenzyme A(it is a derivative of acetic acid). Next, this substance reacts with PIKE, forming citric acid (citrate), coenzyme A, protons (accepted by NAD +, which turns into NAD*H) and carbon dioxide. Subsequently, citric acid is oxidized and converted back into PIKE, which reacts with a new molecule of acetyl coenzyme A, and the whole cycle repeats. During this process, energy is accumulated in the form of ATP and NAD*H.

The next stage is the conversion of the energy stored in NAD*H into ATP bond energy. During this process, electrons from NAD*H move through a multi-step electron transport chain to the final acceptor - molecular oxygen. When electrons move from stage to stage, energy is released, which is used to convert ADP into ATP. Since in this process oxidation is associated with phosphorylation, the whole process is called oxidative phosphorylation(this process was discovered by the Russian scientist V.A. Engelhardt; it occurs on the inner membrane of mitochondria). At the end of this process, water is formed. During the oxygen stage, 36 ATP molecules are produced.

Thus, the final products of glucose breakdown are carbon dioxide and water. With the complete breakdown of one glucose molecule, 38 ATP molecules are released. When there is a lack of oxygen in the cell, glucose is oxidized to form lactic acid (for example, during intense muscle work - running, etc.). As a result, only two ATP molecules are formed.

It should be noted that not only glucose molecules can serve as a source of energy. Fatty acids are also oxidized in the cell to acetyl coenzyme A, which enters the Krebs cycle; at the same time, NAD + is also reduced to NAD*H, which is involved in oxidative phosphorylation. When there is an acute shortage of glucose and fatty acids in the cell, many amino acids undergo oxidation. They also produce acetyl coenzyme A or organic acids involved in the Krebs cycle.

At anaerobic dissimilation method there is no oxygen stage, and energy metabolism in anaerobes is called “fermentation”. The end products of dissimilation during fermentation are lactic acid (lactic acid bacteria) or ethyl alcohol (yeast). With this type of exchange, 2 ATP molecules are released from one glucose molecule.

Thus, aerobic respiration is almost 20 times more energetically beneficial than anaerobic respiration.

Photosynthesis. Life on Earth depends entirely on photosynthesis of plants, which supply organic matter and O 2 to all organisms. During photosynthesis, light energy is converted into the energy of chemical bonds.

Photosynthesis- is the formation of organic substances from inorganic substances with the participation of solar energy. This process was discovered by K.A. Timiryazev in the 19th century. The overall equation for photosynthesis is: 6CO 2 + 6H 2 O = C 6 H 12 O 6 + 6O 2.

Photosynthesis occurs in plants that have plastids - chloroplasts. Chloroplasts have two membranes and a matrix inside. They have a well-developed internal membrane with folds between which there are bubbles - thylakoids. Some thylakoids are collected like a stack into groups called grains. Granas contain all photosynthetic structures; in the stroma surrounding the thylakoids there are enzymes that reduce carbon dioxide to glucose. The main pigment of chloroplasts is chlorophyll, which is similar in structure to human heme. Chlorophyll contains a magnesium atom. Chlorophyll absorbs blue and red rays of the spectrum and reflects green ones. Other pigments may also be present: yellow carotenoids and red or blue phycobilins. Carotenoids are masked by chlorophyll; they absorb light that is not available to other pigments and transfer it to chlorophyll.

Chloroplasts contain two photosystems of different structure and composition: photosystem I and II. Photosystem I has a reaction center, which is a chlorophyll molecule complexed with a special protein. This complex absorbs light at a wavelength of 700 nm (hence why it is called the P700 photochemical center). Photosystem II also has a reaction center - the photochemical center P680.

Photosynthesis has two stages: light and dark.

Light stage. Light energy is absorbed by chlorophyll and puts it into an excited state. An electron in the P700 photochemical center absorbs light, moves to a higher energy level and is transferred to NADP + (nicotinamide adenine dinucleotide phosphate), reducing it to NADP*H. In the chlorophyll molecule of photosystem I, “holes” remain - unfilled spaces for electrons. These “holes” are filled with electrons coming from photosystem II. Under the influence of light, the chlorophyll electron in the photochemical center P680 also enters an excited state and begins to move along the chain of electron carriers. Ultimately, this electron comes to photosystem I, filling the empty spaces in it. In this case, the electron loses part of its energy, which is spent on the formation of ATP from ADP.

Also in chloroplasts, under the influence of sunlight, water is split - photolysis, in which electrons are formed (enter photosystem II and take the place of electrons that went into the carrier chain), protons (accepted by NADP +) and oxygen (as a by-product):

2H 2 O = 4H + + 4e – + O 2

Thus, as a result of the light stage, energy is accumulated in the form of ATP and NADP*H, as well as the formation of oxygen.

Dark stage. Does not require light. The carbon dioxide molecule reacts with 1,5 ribulose diphosphate (a derivative of ribose) with the help of enzymes. An intermediate compound C6 is formed, which decomposes with water into two molecules of phosphoglyceric acid (C3). From these substances, fructose is synthesized through complex reactions, which is then converted into glucose. These reactions require 18 molecules of ATP and 12 molecules of NADP*H. Starch and cellulose are formed from glucose in plants. The fixation of CO 2 and its conversion into carbohydrates is cyclic in nature and is called Calvin cycle.

The importance of photosynthesis for agriculture is great - the yield of agricultural crops depends on it. During photosynthesis, the plant uses only 1-2% of solar energy, so there is a huge prospect of increasing yields through the selection of varieties with higher photosynthetic efficiency. To increase the efficiency of photosynthesis, the following is used: artificial lighting (additional illumination with fluorescent lamps on cloudy days or in spring and autumn) in greenhouses; no shading of cultivated plants, maintaining the required distances between plants, etc.

Chemosynthesis. This is the process of formation of organic substances from inorganic substances using energy obtained from the oxidation of inorganic substances. This energy is stored in the form of ATP. Chemosynthesis was discovered by the Russian microbiologist S.N. Vinogradsky in the 19th century (1889-1890). This process is possible in bacteria: sulfur bacteria (oxidize hydrogen sulfide to sulfur and even sulfuric acid); nitrifying bacteria (oxidize ammonia to nitric acid).

DNA replication(DNA doubling). As a result of this process, two double DNA helices are formed, which are no different from the original (mother). First, with the help of a special enzyme (helicase), the DNA double helix is ​​unraveled at the origins of replication. Then, with the participation of the enzyme DNA polymerase, the synthesis of daughter DNA chains occurs. On one of the chains the process goes on continuously - this chain is called the leading chain. The second strand of DNA is synthesized in short fragments ( fragments of Okazaki), which are “stitched” together using special enzymes. This chain is called lagging or retarded.

The area between the two points at which the synthesis of daughter chains begins is called replicon. Eukaryotes have many replicons in their DNA, while prokaryotes have only one replicon. In each replicon you can see replication fork- that part of the DNA molecule that has already unraveled.

Replication is based on a number of principles:

1. complementarity (A-T, C-G) antiparallelism. Each strand of DNA has a specific orientation: one end carries an OH group attached to the 3" carbon in the deoxyribose sugar; the other end of the strand contains a phosphoric acid residue at the 5" position of the sugar. The two DNA strands are oriented in opposite directions, i.e. antiparallel. The DNA polymerase enzyme can move along the template strands in only one direction: from their 3" ends to their 5" ends. Therefore, during the replication process, the simultaneous synthesis of new chains occurs in antiparallel fashion.
2. semi-conservative. Two daughter helices are formed, each of which retains (preserves) unchanged one of the halves of the maternal DNA
3. intermittency. In order for new DNA strands to form, the mother strands must be completely unwound and extended, which is impossible; therefore, replication begins in several places simultaneously.

Protein biosynthesis. An example of plastic metabolism in heterotrophic organisms is protein biosynthesis. All the main processes in the body are associated with proteins, and in each cell there is a constant synthesis of proteins characteristic of a given cell and necessary during a given period of the cell’s life. Information about a protein molecule is encrypted in a DNA molecule using triplets or codons.

Genetic code is a system for recording information about the sequence of amino acids in proteins using the sequence of nucleotides in mRNA.

Code properties:

1. Triplety - each amino acid is encrypted by a sequence of three nucleotides. This sequence is called a triplet or codon.
2. Degeneracy or redundancy - each amino acid is encrypted by more than one codon (from 2 to 6). The exceptions are methionine and tryptophan - each of them is encoded by one triplet.
3. Uniqueness - each codon encodes only one amino acid.
4. Between genes there are “punctuation marks” - these are three special triplets (UAA, UAG, UGA), each of which does not code for amino acids. These triplets are found at the end of each gene. There are no “punctuation marks” inside the gene.
5. Universality - the genetic code is the same for all living creatures on planet Earth.

There are three stages in protein biosynthesis - transcription, post-transcriptional processes and translation.

Transcription is a process of mRNA synthesis carried out by the enzyme RNA polymerase. Occurs in the nucleus. Transcription occurs according to the rule of complementarity. The length of mRNA corresponds to one or more genes. The transcription process can be divided into 4 stages:

1. binding of RNA polymerase to the promoter (this is the site for attachment of the enzyme).
2. initiation - the beginning of synthesis.
3. elongation - growth of an RNA chain; sequential addition of nucleotides to each other in the order in which the complementary nucleotides of the DNA strand appear. Its speed is up to 50 nucleotides per second.
4. termination - completion of pre-i-RNA synthesis.

Posttranscriptional processes. After the formation of pre-mRNA, maturation or processing of i-RNA begins. In this case, intronic regions are removed from the RNA molecule, followed by the joining of exonic regions (this process is called splicing). After this, the mature mRNA leaves the nucleus and goes to the site of protein synthesis (ribosomes).

Broadcast- this is the synthesis of polypeptide chains of proteins, carried out using an mRNA matrix in ribosomes.

Amino acids necessary for protein synthesis are delivered to ribosomes using tRNA. The transfer RNA molecule has the shape of a clover leaf, at the top of which there is a sequence of three nucleotides complementary to the nucleotides of the codon in the mRNA. This sequence is called anticodon. An enzyme (codase) recognizes t-RNA and attaches the corresponding amino acid to it (the energy of one ATP molecule is wasted).

Protein biosynthesis begins (in bacteria) when the AUG codon, located in the first place in the copy of each gene, takes a place on the ribosome in the donor site and a tRNA carrying formylmethionine (this is a modified form of the amino acid methionine) is attached to it. After protein synthesis is completed, formylmethionine is cleaved from the polypeptide chain.

The ribosome has two sites for binding two tRNA molecules: donor And acceptor. t-RNA with an amino acid enters the acceptor site and attaches to its i-RNA codon. The amino acid of this tRNA attaches to itself a growing protein chain, and a peptide bond arises between them. The tRNA to which the growing protein is attached moves along with the mRNA codon to the donor site of the ribosome. A new t-RNA with an amino acid arrives at the vacated acceptor site, and everything repeats again. When one of the punctuation marks appears on the ribosome, none of the tRNAs with an amino acid can occupy the acceptor site. The polypeptide chain breaks off and leaves the ribosome.

Cells of different tissues of the body produce different proteins (amylase - cells of the salivary glands; insulin - cells of the pancreas, etc.). In this case, all the cells of the body were formed from one fertilized egg through repeated division using mitosis, i.e. have the same genetic makeup. These differences are due to the fact that different sections of DNA are transcribed in different cells, i.e. Different mRNAs are formed, which are used to synthesize proteins. The specialization of a cell is not determined by all genes, but only by those from which the information was read and implemented into proteins. Thus, in each cell only part of the hereditary information is realized, and not all of the information.

Regulation of gene activity during the synthesis of individual proteins using the example of bacteria (scheme by F. Jacob and J. Monod).

It is known that until sugar is added to the nutrient medium where the bacteria live, the bacterial cell does not have the enzymes necessary to break it down. But a few seconds after adding sugar, all the necessary enzymes are synthesized in the cell.

Enzymes involved in one chain of conversion of the substrate into the final product are encoded in sequences located one after the other. structural genes one operon. Operon is a group of genes that carry information about the structure of proteins necessary to perform one function. Between the structural genes and the promoter (the landing site of RNA polymerase) there is a region called operator. It is so called because it is where the synthesis of mRNA begins. A special protein interacts with the operator - repressor (suppressor). While the repressor is on the operator, mRNA synthesis cannot begin.

When a substrate enters the cell, the breakdown of which requires proteins encoded in the structural genes of a given operon, one of the substrate molecules interacts with the repressor. The repressor loses the ability to interact with the operator and moves away from it; the synthesis of mRNA and the formation of corresponding proteins on the ribosome begins. As soon as the last molecule of the substrate is converted into the final substance, the released repressor will return to the operator and block the synthesis of mRNA.

References:

1. Yu. Chentsov “Introduction to Cell Biology” (2006)
2. V.N. Yarygin (editor) “Biology” (in two volumes, 2006)
3. O.V. Aleksandrovskaya et al. “Cytology, histology and embryology” (1987)
4. A.O. Ruvimsky (editor) “General Biology” (a textbook for grades 10-11 with in-depth study of biology) - in my opinion, this is one of the best textbooks on general biology for applicants, although not without its shortcomings.

Over the past 4045 years, cytology has transformed from descriptive and morphological into an experimental science that sets itself the task of studying the physiology of a cell, its basic vital functions and the properties of its biology. In other words, this is the physiology of the cell. Carnoy Biology of the Cell published in 1884. Let us highlight some important milestones in the history of the study of cell biology.

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Lecture No. 1

INTRODUCTION TO CYTOLOGY

Subject and objectives of the cytology course.

The place of cytology in the system of biological disciplines

Cytology (from Greek. Kytos cell, cell) science of the cell. Modern cytology studies the structure of cells, their functioning as elementary living systems; explores the functions of individual cellular components, the processes of cell reproduction, their adaptation to environmental conditions, and many other processes that make it possible to judge the properties and functions common to all cells.

Cytology also examines the characteristics of specialized cells, the stages of formation of their special functions and the development of specific cellular structures.

Over the past 40-45 years, cytology has transformed from descriptive and morphological into an experimental science, setting itself the task of studying the physiology of the cell, its basic vital functions and properties, and its biology. In other words, this is the physiology of the cell.

The possibility of such a switch in the interests of researchers arose due to the fact that cytology is closely related to the scientific and methodological achievements of biochemistry, biophysics, molecular biology and genetics.

In general, cytology is closely related to almost all biological disciplines, since everything living on Earth (almost everything!) has a cellular structure, and cytology is precisely the study of cells in all their diversity.

Cytology is closely related to zoology and botany, since it studies the structural features of plant and animal cells; with embryology in the study of the structure of germ cells; with histology cell structure of individual tissues; with anatomy and physiology, since on the basis of cytological knowledge the structure of certain organs and their functioning is studied.

The cell has a rich chemical composition, complex biochemical processes take place in it: photosynthesis, protein biosynthesis, respiration, and also important physical phenomena occur, in particular, the occurrence of excitation, a nerve impulse, therefore cytology is closely related to biochemistry and biophysics.

To understand the complex mechanisms of heredity, it is necessary to study and understand their material carriers - genes, DNA, which are integral components of cellular structures. From this arises a close connection between cytology and genetics and molecular biology.

Data from cytological studies are widely used in medicine, agriculture, veterinary medicine, and in various industries (food, pharmaceutical, perfumery, etc.). Cytology also occupies an important place in the teaching of biology at school (general biology course in high school).

Brief historical sketch of the development of cytology

In general, cytology is a fairly young science. It emerged from other biological sciences a little over a hundred years ago. For the first time, generalized information about the structure of cells was collected in the book by Zh.B. Carnoy’s “Biology of the Cell,” published in 1884. The appearance of this book was preceded by a long and stormy period of searches, discoveries, and discussions, which led to the formulation of the so-called cell theory, which has enormous general biological significance.

Let us highlight some important milestones in the history of the study of cell biology.

The end of the 16th and the beginning of the 17th century. According to various sources, the inventors of the microscope are Zacharias Jansen (1590, Holland), Galileo Galilei (1610, Italy), Cornelius Drebbel (1619-1620, Holland). The first microscopes were very bulky and expensive and were used by noble people for their own entertainment. But gradually they improved and began to turn from a toy into a scientific research tool.

1665 Robert Hooke (England), using a microscope designed by the English physicist H. Huygens, studied the structure of cork and for the first time used the term “cell” to describe the structural units that make up this tissue. He believed that cells are empty, and living matter is cell walls.

1675-1682 M. Malpighi and N. Grew (Italy) confirmed the cellular structure of plants

1674 Antonio van Leeuwenhoek (Holland) discovered single-celled organisms, including bacteria (1676). He was the first to see and describe animal cells - red blood cells, sperm.

1827 Dolland dramatically improved the quality of lenses. After this, interest in microscopy quickly grew and spread.

1825 Jan Purkinė (Czech Republic) is the first to describe the cell nucleus in the egg of birds. He calls it the “germinal vesicle” and assigns to it the function of “the productive force of the egg.”

1827 Russian scientist Karl Baer discovered the mammalian egg and established that all multicellular organisms begin their development from a single cell. This discovery showed that the cell is the unit not only of structure, but also of development of all living organisms.

1831 Robert Brown (English botanist) first described the nucleus in plant cells. He came up with the name “nucleus” “nucleus” and for the first time stated that it was a common component of any cell, having some essential significance for its life.

1836 Gabriel Valentin, a student of Purkin, discovers the nucleus of animal cells cells of the epithelium of the conjunctiva, the connective membrane of the eye. Inside this “nucleus” he finds and describes the nucleolus.

From that moment on, the nucleus began to be sought out and found in all tissues of plants and animals.

1839 Theodor Schwann (German physiologist and cytologist) published the book “Microscopic studies on the correspondence in the structure and growth of animals and plants,” in which he summarized the existing knowledge about the cell, including the results of research by the German botanist Matthias Jakob Schleiden on the role of the nucleus in plant cells. The main idea of ​​the book (stunning in its simplicity) life is concentrated in cells caused a revolution in biology. In other words, T. Schwann and M. Schleiden formulated the cell theory. Its main provisions then were as follows:

1) both plant and animal organisms consist of cells;

2) cells of plant and animal organisms develop similarly and are close to each other in structure and functional purpose;

3) each cell is capable of independent life.

Cell theory is one of the outstanding generalizations of biology XIX century, which provided the basis for understanding life and revealing the evolutionary connections between organisms.

1840 Jan Purkynė proposed the name “protoplasm” for the cellular contents, making sure that it (and not the cell walls) constituted living matter. Later the term "cytoplasm" was introduced.

1858 Rudolf Virchow (German pathologist and social activist) showed that all cells are formed from other cells through cell division. This position was later also included in the cell theory.

1866 Ernst Haeckel (German biologist, founder of the phylogenetic direction of Darwinism) established that the storage and transmission of hereditary characteristics is carried out by the nucleus.

1866-1888 Cell division was studied in detail and chromosomes were described.

1880-1883 Plastids, in particular chloroplasts, were discovered.

1876 ​​Cell center opened.

1989 Golgi apparatus discovered.

1894 Mitochondria discovered.

1887-1900 The microscope has been improved, as have the methods of fixation, staining of specimens, and preparation of sections. Cytology began to acquire an experimental character. Embryological research is being conducted to determine how cells interact with each other during the growth of a multicellular organism.

1900 Mendel's laws, forgotten since 1865, were rediscovered, and this gave impetus to the development of cytogenetics, which studies the role of the nucleus in the transmission of hereditary characteristics.

The light microscope by this time had almost reached the theoretical limit of resolution; The development of cytology naturally slowed down.

1930s The electron microscope was introduced.

From 1946 to the present day, the electron microscope has become widespread in biology, making it possible to study the structure of the cell in much more detail. This “fine” structure began to be called ultrastructure.

The role of domestic scientists in the development of the doctrine of the cell.

Caspar Friedrich Wolf (1733-1794) member of the St. Petersburg Academy of Sciences, opposed metaphysical ideas about development as the growth of a ready-made organism embedded in the reproductive cell (the theory of preformationism).

P.F. Goryaninov is a Russian biologist who described various forms of cells and, even before Schwann and Schleiden, expressed views close to them.

Second half of the 19th century V. beginning of the twentieth century: Russian cytologist I.D. Chistyakov was the first to describe mitosis in moss spores; I.N. Gorozhankin studied the cytological basis of fertilization in plants; S.T. Navashin discovered double fertilization in plants in 1898.

Basic provisions of modern cell theory

1. The cell, as an elementary living system capable of self-renewal, self-regulation and self-reproduction, underlies the structure and development of all living organisms.

2. The cells of all organisms are built according to a single principle, similar (homologous) in chemical composition, basic manifestations of life activity and metabolism.

3. Cell reproduction occurs through cell division, and each new cell is formed as a result of the division of the mother cell.

4. In multicellular organisms, cells are specialized in the functions they perform and form tissues. Organs and organ systems that are closely interconnected are made up of tissues.

With the development of science, only one position of the cell theory turned out to be not absolutely true - the first. Not all living organisms have a cellular organization. This became clear with the discovery of viruses. This is a non-cellular form of life, but the existence and reproduction of viruses is only possible using the enzymatic systems of cells. Therefore, a virus is not an elementary unit of living matter.

The cellular form of organization of living things, having once emerged, became the basis for all further development of the organic world. The evolution of bacteria, protozoa, blue-green algae and other organisms occurred entirely due to the structural, functional and biochemical transformations of the cell. During this evolution, an amazing variety of cell forms was achieved, but the general plan of the cell structure did not undergo fundamental changes.

The emergence of multicellularity dramatically expanded the possibilities for the progressive evolution of organic forms. The leading changes here were in higher order systems (tissues, organs, individuals, populations, etc.). At the same time, the tissue cells acquired features that were useful for the individual and the species as a whole, regardless of how this feature affected the viability and ability to reproduce the tissue cells themselves. As a result, the cell became a subordinate part of the whole organism. For example, the functioning of a number of cells is associated with their death (secretory cells), loss of the ability to reproduce (nerve cells), and loss of the nucleus (mammalian red blood cells).

Methods of modern cytology

Cytology arose as a branch of microanatomy, and therefore the main method that cytologists use is the method of light microscopy. Currently, this method has found a number of additions and modifications, which has significantly expanded the range of tasks and issues solved by cytology. A revolutionary moment in the development of modern cytology and biology in general was the use of electron microscopy, which opened up unusually broad prospects. With the introduction of electron microscopy, in some cases it is already difficult to draw the line between cytology proper and biochemistry; they are combined at the level of macromolecular study of objects (for example, microtubules, membranes, microfilaments, etc.). Nevertheless, the main methodological technique in cytology remains visual observation of the object. In addition, cytology uses numerous techniques of preparative and analytical biochemistry and methods of biophysics.

Let's get acquainted with some methods of cytological research, which, for ease of study, will be divided into several groups.

I . Optical methods.

1. Light microscopy.Objects of study: preparations that can be viewed in transmitted light. They should be sufficiently transparent, thin and contrasting. Biological objects do not always have these qualities. To study them in a biological microscope, it is necessary to first prepare the appropriate preparations by fixation, dehydration, making thin sections, and staining. The cellular structures in such fixed preparations do not always correspond to the true structures of a living cell. Their study should be accompanied by the study of a living object in dark-field and phase-contrast microscopes, where the contrast is increased due to additional devices to the optical system.

The maximum resolution that a biological microscope can provide under oil immersion is 1700 Ǻ (0.17 μm) in monochromatic light and 2500 Ǻ (0.25 μm) in white light. A further increase in resolution can only be achieved by reducing the wavelength of light.

2. Dark-field microscopy. The method is based on the principle of light scattering at the boundary between phases with different refractive indices. This is achieved in a dark-field microscope or in a conventional biological microscope using a special dark-field condenser, which transmits only very oblique edge rays of the light source. Because the edge rays are highly inclined, they do not enter the lens, and the field of view of the microscope appears dark, while an object illuminated by scattered light appears light. Cell preparations usually contain structures of different optical densities. Against a general dark background, these structures are clearly visible due to their different glow, and they glow because they scatter the rays of light falling on them (Tyndall effect).

Living objects can be studied in a dark field. The resolution of such a microscope is high (less than 0.2 microns).

3. Phase contrast microscopy. The method is based on the fact that individual areas of a transparent drug differ from the environment in refractive index. Therefore, light passing through them travels at different speeds, i.e. experiences a phase shift, which is reflected in a change in brightness. Particles with a refractive index greater than the refractive index of the medium produce dark images on a light background, while particles with an index less than that of the medium produce images lighter than the surrounding background.

Phase contrast microscopy reveals many details and features of living cells and tissue sections. This method is of great importance for studying tissues cultured in vitro.

4. Interference microscopy. This method is close to the method of phase contrast microscopy and makes it possible to obtain contrast images of unstained transparent living cells, as well as calculate the dry weight of the cells. An interference microscope is designed in such a way that a beam of parallel light rays from the illuminator is divided into two streams. One of them passes through the object and acquires changes in the oscillation phase, the other goes bypassing the object. In the lens prisms, both flows are reconnected and interfere with each other. As a result of interference, an image will be built in which areas of the cell with different thicknesses or different densities will differ from each other in the degree of contrast. In this device, by measuring phase shifts, it is possible to determine the concentration and mass of dry matter in an object.

II . Vital (intravital) study of cells.

1. Preparation of live cell preparations.A light microscope allows you to see living cells. For short-term observation, cells are simply placed in a liquid medium on a glass slide; If long-term observation of cells is required, special cameras are used. In any of these cases, cells are studied in specially selected media (water, saline, Ringer's solution, etc.).

2. Cell culture method. Cultivation of cells and tissues outside the body ( in vitro ) is subject to compliance with certain conditions; a suitable nutrient medium is selected, a strictly defined temperature is maintained (about 20 0 for cells of cold-blooded animals and about 37 0 for warm-blooded animals), it is mandatory to maintain sterility and regularly reseed the culture on a fresh nutrient medium. Nowadays, the method of culturing cells outside the body is widely used not only for cytological, but also for genetic, virological and biochemical studies.

3. Microsurgery methods. These methods involve surgical action on the cell. Microoperations on individual small cells began to be carried out from the beginning of the twentieth century, when a device calledmicromanipulator.With its help, cells are cut, individual parts are removed from them, substances are injected (microinjection), etc. The micromanipulator is combined with a conventional microscope, through which the progress of the operation is monitored. Microsurgical instruments are glass hooks, needles, capillaries, which have microscopic dimensions. In addition to mechanical effects on cells, microbeams of ultraviolet light or laser microbeams have recently been widely used in microsurgery. This makes it possible to almost instantly inactivate individual areas of a living cell.

4. Intravital staining methods. When studying living cells, they try to stain them using so-called vital dyes. These are dyes of an acidic (trypan blue, lithium carmine) or basic (neutral red, methylene blue) nature, used at very high dilutions (1:200,000), therefore, the influence of the dye on the vital activity of the cell is minimal. When staining living cells, the dye collects in the cytoplasm in the form of granules, and in damaged or dead cells, diffuse staining of the cytoplasm and nucleus occurs. The time for staining preparations varies greatly, but for most vital dyes it is from 15 to 60 minutes.

III . Cytophysical methods

1. X-ray absorption method. The method is based on the fact that different substances at a certain wavelength absorb X-rays differently. By passing X-rays through a tissue specimen, its chemical composition can be determined from its absorption spectrum.

2. Fluorescence microscopy. The method is based on the property of some substances to fluoresce in ultraviolet rays. For these purposes, an ultraviolet microscope is used, in the condenser of which a light filter is installed that separates blue and ultraviolet rays from the general light beam. Another filter placed in front of the observer's eyes absorbs these rays, allowing fluorescence rays emitted by the drug to pass through. The light source is mercury lamps and incandescent lamps, which produce strong ultraviolet radiation in the overall light beam.

Fluorescence microscopy makes it possible to study a living cell. A number of structures and substances contained in cells have their own (primary) fluorescence (chlorophyll, vitamins A, B 1 and B 2 , some hormones and bacterial pigments). Objects that do not have their own fluorescence can be tinted with special fluorescent dyes fluorochromes . Then they are visible in ultraviolet light (secondary fluorescence). Using this method, you can see the shape of the object, the distribution of fluorescent substances in the object, and the content of these substances).

3. Radiography method. The method is based on the fact that radioactive isotopes, when introduced into the body, enter into general cellular metabolism and are included in the molecules of the corresponding substances. The locations of their localization are determined by the radiation given by isotopes and detected by the illumination of a photographic plate when it is applied to the preparation. The drug is manufactured some time after the introduction of the isotope, taking into account the time of passage of certain stages of metabolism. This method is widely used to determine the localization of sites of biopolymer synthesis, to determine the pathways of substance transfer in a cell, and to monitor the migration or properties of individual cells.

IV . Methods for studying ultrastructure

1. Polarization microscopy. The method is based on the ability of various components of cells and tissues to refract polarized light. Some cellular structures, such as spindle filaments, myofibrils, cilia of the ciliated epithelium, etc., are characterized by a certain orientation of molecules and have the property of birefringence. These are the so-calledanisotropic structures.

A polarizing microscope differs from a conventional biological microscope in that a polarizer is placed in front of the condenser, and a compensator and analyzer are placed behind the specimen and lens, allowing a detailed study of birefringence in the object under consideration. The polarizer and analyzer are prisms made of Iceland spar (Nicolas prisms). A polarizing microscope makes it possible to determine the orientation of particles in cells and other structures, to clearly see structures with birefringence, and with appropriate processing of preparations, observations can be made on the molecular organization of a particular part of the cell.

2. X-ray diffraction analysis method. The method is based on the property of X-rays to undergo diffraction when passing through crystals. They undergo the same diffraction if biological objects, such as tendon, cellulose, and others, are placed instead of crystals. A series of rings, concentrically located spots and stripes appear on the screen or photographic plate. The diffraction angle is determined by the distance between groups of atoms and molecules in an object. The greater the distance between structural units, the smaller the diffraction angle, and vice versa. On the screen, this corresponds to the distance between the dark areas and the center. Oriented particles give circles, sickles, and points on the diagram; unoriented particles in amorphous substances give the image of concentric rings.

The X-ray diffraction method is used to study the structure of molecules of proteins, nucleic acids and other substances that make up the cytoplasm and nucleus of cells. It makes it possible to determine the spatial arrangement of molecules, accurately measure the distance between them and study the intramolecular structure.

3. Electron microscopy. Considering the characteristics of a light microscope, one can be convinced that the only way to increase the resolution of an optical system is to use an illumination source that emits wavelengths with the shortest wavelength. Such a source can be a hot filament, which in an electric field emits a stream of electrons, the latter can be focused by passing it through a magnetic field. This served as the basis for the creation of the electron microscope in 1933. The main difference between an electron microscope and a light microscope is that it uses a fast flow of electrons instead of light, and electromagnetic fields replace glass lenses. The image is produced by electrons that have passed through the object and are not rejected by it. In modern electron microscopes, a resolution of 1Ǻ (0.1 nm) has been achieved.

Non-living objects preparations are viewed under an electron microscope. It is not yet possible to study living objects, because objects are placed in a vacuum, which is fatal to living organisms. In a vacuum, electrons hit an object without scattering.

Objects studied under an electron microscope must have a very small thickness, no more than 400-500 Ǻ (0.04-0.05 μm), otherwise they turn out to be impenetrable to electrons. For these purposes they useultramicrotomes, the operating principle of which is based on the thermal expansion of the rod that feeds the knife to the object or, conversely, the object to the knife. Specially sharpened small diamonds are used as knives.

Biological objects, especially viruses, phages, nucleic acids, thin membranes, have a weak ability to scatter electrons, i.e. low contrast. Their contrast is increased by sputtering the object with heavy metals (gold, platinum, chromium), carbon sputtering, by treating preparations with osmic or tungstic acids and some salts of heavy metals.

4. Special methods of electron microscopy of biological objects. Currently, electron microscopy methods are being developed and improved.

Freezing method etchingconsists in the fact that the object is first quickly frozen with liquid nitrogen, and then at the same temperature is transferred to a special vacuum installation. There, the frozen object is mechanically chipped with a cooled knife. This exposes the internal zones of frozen cells. In a vacuum, part of the water that has passed into a glassy form is sublimated (“etching”), and the surface of the chip is successively covered with a thin layer of evaporated carbon and then metal. In this way, an impression film is obtained that repeats the intravital structure of the material, which is studied in an electron microscope.

High-voltage microscopy methodselectron microscopes with an accelerating voltage of 1-3 million V have been designed. The advantage of this class of devices is that at high energy electrons, which are less absorbed by the object, samples of greater thickness (1-10 microns) can be examined. This method is also promising in another respect: if the ultra-high energy of electrons reduces their impact on the object, then in principle this can be used in studying the ultrastructure of living objects. Work is currently underway in this direction.

Scanning (raster) electron microscopy methodallows you to study a three-dimensional picture of the cell surface. In this method, a fixed and specially dried object is covered with a thin layer of evaporated metal (most often gold), a thin beam of electrons runs along the surface of the object, is reflected from it and hits a receiving device, which transmits the signal to a cathode ray tube. Thanks to the enormous depth of focus of a scanning microscope, which is much larger than that of a transmission microscope, an almost three-dimensional image of the surface under study is obtained.

V . Cyto- and histochemical methods.

Using such methods, it is possible to determine the content and localization of substances in a cell using chemical reagents that, together with the identified substance, produce a new substance of a specific color. The methods are similar to the methods for determining substances in analytical chemistry, but the reaction occurs directly on the tissue preparation, and precisely in the place where the desired substance is localized.

The amount of the final product of a cytochemical reaction can be determined usingcytophotometry method.It is based on determining the amount of chemical substances based on their absorption of light of a certain wavelength. It was found that the intensity of absorption of rays is proportional to the concentration of the substance for the same thickness of the object. Therefore, by assessing the degree of light absorption by a given substance, it is possible to find out its quantity. For this type of research, instruments are used: microscopes-cytophotometers; They have a sensitive photometer behind the lens that records the intensity of the light flux passing through the lens. Knowing the area or volume of the measured structure and the absorption value, it is possible to determine both the concentration of a given substance and its absolute content.

Quantitative fluorometry techniques have been developed that make it possible to determine the content of substances with which fluorochromes bind by the degree of luminescence. Thus, to identify specific proteins, they useimmunofluorescence methodimmunochemical reactions using fluorescent antibodies. This method has very high specificity and sensitivity. It can be used to identify not only proteins, but also individual nucleotide sequences in DNA or to determine the localization of RNADNA hybrid molecules.

VI . Cell fractionation.

In cytology, various methods of biochemistry, both analytical and preparative, are widely used. In the latter case, it is possible to obtain various cellular components in the form of separate fractions and study their chemistry, ultrastructure and properties. Thus, at present, almost any cellular organelles and structures are obtained in the form of pure fractions: nuclei, nucleoli, chromatin, nuclear membranes, plasma membrane, ER vacuoles, ribosomes, Golgi apparatus, mitochondria, their membranes, plastids, microtubules, lysosomes, etc. d.

Obtaining cell fractions begins with the general destruction of the cell, with its homogenization. Fractions can then be isolated from the homogenates. One of the main methods for isolating cellular structures is differential (separation) centrifugation. The principle of its application is that the time for particles to settle in a homogenate depends on their size and density: the larger the particle or the heavier it is, the faster it will settle to the bottom of the test tube. The resulting fractions, before being analyzed by biochemical methods, must be checked for purity using an electron microscope.

A cell is the elementary unit of living things.

Prokaryotes and eukaryotes

The cell is a self-replicating system. It contains cytoplasm and genetic material in the form of DNA. DNA regulates the life of the cell and reproduces itself, due to which new cells are formed.

Cell sizes . Bacteria diameter 0.2 microns. More often the cells are 10-100 microns, less often 1-10 mm. There are very large ones: eggs of ostriches, penguins, geese - 10-20 cm, nerve cells and milky vessels of plants - up to 1 m or more.

Cell shape : round (liver cells), oval (amphibian red blood cells), multifaceted (some plant cells), stellate (neurons, melanophores), disc-shaped (human red blood cells), spindle-shaped (smooth muscle cells), etc.

But, despite the variety of shapes and sizes, the organization of cells of all living organisms is subject to common structural principles: a protoplast, consisting of cytoplasm and nucleus, and a plasma membrane. Cytoplasm, in turn, includes hyaloplasm, organelles (general organelles and special-purpose organelles) and inclusions.

Depending on the structural features of their constituent parts, all cells are divided intoprokaryotic And eukaryotic.

Prokaryotic cells are characteristic of bacteria and blue-green algae (cyanobacteria). They do not have a true nucleus, nucleoli and chromosomes, they only have nucleoid , devoid of a shell and consisting of a single circular DNA molecule associated with a small amount of protein. Prokaryotes lack membrane organelles: mitochondria, EPS, chloroplasts, lysosomes and the Golgi complex. There are only smaller ribosomes than eukaryotes.

On top of the plasma membrane, prokaryotes have a rigid cell wall and, often, a mucous capsule. The plasma membrane forms invaginations mesosomes , on the membranes of which redox enzymes are located, and in photosynthetic prokaryotes the corresponding pigments (bacteriochlorophyll in bacteria, chlorophyll and phycocyanin in cyanobacteria). Thus, these membranes perform the functions of mitochondria, chloroplasts and other organelles.

Eukaryotes include unicellular animals (protists), fungi, plants, and animals. In addition to the core clearly delimited by a double membrane, they have many other membrane structures. Based on the number of membranes, organelles of eukaryotic cells can be divided into three main groups: single-membrane (ER, Golgi complex, lysosomes), double-membrane (mitochondria, plastids, nucleus), non-membrane (ribosomes, cell center). In addition, the entire cytoplasm is divided by internal membranes into reaction spaces compartments (compartments). In these compartments, various chemical reactions occur simultaneously and independently of each other.

Comparative characteristics of various types

eukaryotic cells (from Lemez, Lisov, 1997)

Signs	Cells
		protist	mushrooms	plants	animals
Cell wall Large vacuole Chloroplasts Way nutrition Centrioles Reserve nutrient carbohydrate	many have rarely happen often auto- and heterotrophic there are often starch, glycogen, paramyl, chrysolaminerin	mainly from chitin There is heterotroph- new there are rarely glycogen	from cellulose There is There is autotrophic only in some mosses and ferns starch	heterotrophic There is glycogen

Similarities and differences between animal and plant cells

Plant and animal cells are similar in the following ways:

1). General plan of the cell structure presence of a cytoplasmic membrane, cytoplasm, nucleus.

2). A unified plan for the structure of the cytoplasmic membrane, built according to the fluid-mosaic principle.

3). Common organelles: ribosomes, mitochondria, ER, Golgi complex, lysosomes.

4). The commonality of life processes metabolism, reproduction, growth, irritability, etc.

At the same time, plant and animal cells differ:

1). In form: plants are more uniform, animals are very diverse.

2). By size: plant larger, animal small.

3). According to their location in tissues: plants are tightly adjacent to each other, animals are loosely located.

4). Plant cells have an additional cellulose wall.

5). Plant cells have large vacuoles. In animals, if they exist, they are small and appear during the aging process.

6). Plant cells have turgor and are elastic. Animals soft.

7). Plant cells contain plastids.

8). Plant cells are capable of autotrophic nutrition, while animal cells are heterotrophs.

9). Plants do not have centrioles (except for some mosses and ferns), animals always have them.

10). Plant cells have unlimited growth.

eleven). Plant cells accumulate starch as a reserve nutrient; animal cells accumulate glycogen.

12). In animal cells there is a glycocalyx on top of the cytoplasmic membrane, but in plant cells it is not.

13). ATP synthesis in animal cells occurs in mitochondria, in plant cells in mitochondria and plastids.

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The main feature of the morpho-functional method for studying cells is the desire to understand the structural basis of the biochemical processes that determine a given function, i.e., to connect these processes with specific cellular structures.

The ultimate goal with this method is identical to the goal pursued by molecular biology and cellular structural biochemistry. However, the methods used by these sciences to solve a common problem are fundamentally different. If in molecular biology and structural biochemistry an indispensable condition is the destruction of the cell and the isolation of the structure being studied in the form of a more or less pure fraction, then in cytological studies the prerequisite, on the contrary, is the preservation of the integrity of the cell. In this case, it is necessary to strive to reduce external interference to a minimum, and try to study the structural and biochemical organization of certain components within the entire cellular system.

Research into the morphofunctional direction has developed rapidly over the past decades. At this time, a large number of fundamentally new methods for qualitative and quantitative analysis of cellular structures were developed. This approach is closely related to new branches of biological sciences and, in particular, to molecular biology, which determines the very significant contribution of such research to the progress of our knowledge about the general laws of cell organization.

Electron microscopy

One of the most common, which has become a classical method used in structural and biochemical studies, is the method of electron microscopy in its various modifications. These modifications are due to both different approaches to the analysis of the structures under study and the peculiarities of preparing cells for ultrastructural studies. The high resolutions of conventional transmission (transmission) microscopes make it possible to analyze not only all organelles of the nuclear and cytoplasmic apparatus, but also some structures located at the supramolecular level of organization, for example, supporting and contractile microfibrils, microtubules, and some multienzyme complexes. Currently, the method of high-voltage electron microscopy is increasingly being successfully used to study cells at the systemic and subsystemic levels of their organization. Due to the much higher energy of the penetrating electron beam compared to a transmission electron microscope, this method makes it possible to study “thick” sections or even entire spread-out cells under a microscope, which allows, for example, to analyze the overall complex system of submembrane fibrils of the cell surface apparatus.

In the study of the function of the surface apparatus of the cell, the relationship of individual subsystems of the surface apparatus of the nucleus and a number of other issues of general cytology, the method of scanning electron microscopy, which makes it possible to study the surface of an object in volume, acquires significant importance.

Freeze-chip method

A special and fundamentally important place in cytological studies of the morphobiochemical direction is occupied by the freezing-cleavage method. It is the most gentle method for preparing biological objects for ultrastructural analysis, i.e., it causes minimal changes in cellular structures compared to their native state. The essence of the method is as follows. The object is placed in an atmosphere of liquid nitrogen, which instantly stops all metabolic processes. Then chips are made from the frozen object. Replicas are obtained from the surface of chips by applying a metal film to them. These films are subsequently examined under an electron microscope. The advantage of the freezing-cleavage method is that the cleavage plane usually passes through the hydrophobic phase of the membrane, and this makes it possible to study the quantity, size and nature of the arrangement of integral membrane proteins, i.e. directly the internal morphobiochemical organization of membranes, on the cleavages. The method gave very valuable results in the study of various types of membrane structures and special formations, for example, certain types of cell contacts.

Cytochemical method

For the main task of the structural-biochemical aspect of cytological research - elucidating the functional significance of structures through analysis of their biochemical organization - cytochemical methods play an extremely important role. Currently, they are continuously being improved both in the sense of accurate qualitative identification of chemical compounds in the structures under study, and in the sense of their quantitative assessment. Using special instruments that allow quantitative cytospectrophotometry, it is possible to determine the content of a given substance, for example RNA and DNA, not only in the cell as a whole, but also at the level of nuclear or cytoplasmic structures. Thanks to interference microscopy, it is possible to assess the total amount of protein in a cell and its changes during its life.

There is a method of cytochemical identification of enzymes, which allows one to judge not only the localization and quantity of a particular compound in cellular structures, but also the processes of synthesis and intracellular transport of these compounds.

The cytochemistry of enzymes is based on the principle of substrate-enzyme interaction using marker compounds that precipitate. By determining the localization, and in some cases, the activity of enzymatic systems, we can judge the localization of certain biochemical processes in cellular structures.

Autoradiography

The autoradiography method, just like the cytochemistry of enzymes, opens up the possibility of studying intracellular synthesis and transport, but at the same time it has even broader possibilities. The autograph method is based on the use of radioactive precursors for the synthesis of macromolecules labeled with artificial isotopes (3 H, 14 C, 35 S, etc.). It allows not only to localize the sites of synthesis of certain macromolecules, but also to trace specific pathways of intracellular transport of these compounds, to give a relative quantitative assessment of the intensity of synthesis and the speed of movement of macromolecules in cellular structures. In this way, in particular, the movement of RNA from the nucleus into the cytoplasm of cells was shown for the first time, the localization of synthesis and intracellular transport of secretions in secretory cells were traced in detail, and many other facts important for general cytology were revealed. At its core, this method is one of the most typical methods characteristic of the structural-biochemical direction of research, since it allows one to directly study metabolic processes in intracellular structures in an intact, undamaged (as in biochemical studies) cell. The essence of this method is based on the detection of molecules labeled with an artificial isotope using a photographic emulsion, which covers sections of cells and tissues fixed at different times after the introduction of the labeled precursor.

Immunocytochemical method

Currently, a very accurate qualitative analysis of individual proteins of cellular structures within the entire cellular system is possible. This analysis is carried out using immunocytochemical methods. The essence of these methods is that a specific protein serves as an antigen, to which specific antibodies are produced in the body of any mammal. The latter are combined with a fluorescent dye or other marker. Then the cell under study is treated with serum containing labeled antibodies. Specific labeled antibodies bind strictly selectively to structures containing the proteins being studied. Using this method, in particular, the localization of the main and auxiliary contractile proteins of the actin-myosin system in the submembrane fibrillar apparatus of cells was revealed, and modification of their distribution during the formation of the mitotic apparatus and in the process of cytotomy was shown. The same method was successfully used to prove the validity of the fluid-mosaic model of membrane organization.

Comprehensive cell research methods

Recently, especially great successes in the study of the structural and biochemical organization of cells have been achieved with the integrated use of ultrastructural analysis methods and methods of cytochemistry and autoradiography. These successes are mainly due to the development of special methods of cytochemistry and autoradiography at the ultrastructural level, which make it possible to directly analyze metabolic processes at the named level of cell organization, “structure” biochemical processes, and find out the specific meaning of certain cellular structures in individual links of complex processes of intracellular metabolism. In this regard, extensive material has been accumulated on the role of various varieties of the membrane phase of the cytoplasm in synthetic anabolic processes and processes of intracellular catabolism.

Major advances have been achieved, in particular, in the study of the organization and functioning of the lysosomal apparatus of cells. Important new facts were obtained during the study of the nuclear apparatus of cells. Using cytochemical methods, it is possible to identify ribonucleoproteins (RNPs) and deoxyribonucleoproteins (DNPs) at the ultrastructural level and thereby make significant progress in studying the organization of transcription, maturation and intranuclear transport of various types of RNPs in eukaryotic cells, and the use of the electronic autoradiography made it possible to detail the role of individual cellular structures in these processes. For example, it was possible to study in detail the function of the nucleolus and specifically structure the processes of formation of ribosomal RNA in it.

Such a synthesis of molecular biological and structural biochemical aspects and methods is also very typical for the development of many other important questions about the fine organization of individual cell components. At the same time, the close connection between molecular biological and morphobiochemical cytological analysis is manifested not only in the synthesis of the final results, but also in their interaction during the research process itself. Such interaction is carried out either by carrying out complex work using both biochemical and cytological methods by specialist biochemists and cytologists, or by using special complex methods that are on the border of biochemical and cytological analysis of cellular structures.

An example of the first type is the combination of methods of biochemical isolation of cell components with their fine ultrastructural analysis. In this way, photographs of working genes with the identification of DNA, RNA polymerases and transcribed RNA molecules were obtained for the first time. The improvement of this method now allows, in some cases, to take into account the intensity of transcription by directly counting the number of RNA polymerase complexes. Using an electron microscope, you can directly study patterns of DNA replication on circular or linear DNA molecules isolated by biochemical methods. Ultrastructural analysis methods are also widely used in immunocytochemical studies of the localization of individual proteins, in ribosomal subparticles, in the study of various levels of DNP organization, and in many other cases.

A typical example of specially developed complex methods is the hybridization of DNA and RNA on sections. Its essence is as follows. DNA, which is part of the DNP of a whole cell, is denatured and then processed with RNA fractions labeled with radioactive isotopes. As a result of this, areas on DNA are autoradiographically detected that are complementary to these RNA fractions, i.e., the sites of transcription of the latter, in other words, it becomes possible to accurately determine the localization of certain genes.

Within the experimental method, the functional organization of the cell as a whole or its individual components is studied by changing its state with the help of external influences. By then observing changes in the vital activity of the cell or its components, one can draw conclusions about certain properties of the mechanisms being studied. This kind of method has now become very widespread in some sections of cytology, and in some of its areas the cytophysiological aspect of the analysis of cellular structures still occupies a dominant position.

This is precisely the state of the problem regarding the transport function of the cell surface apparatus. On the one hand, significant progress has been made in the study of this issue: based on the results of cytophysiological analysis, it was possible to identify types of transmembrane transport of substances and characterize various properties of transport systems. On the other hand, a final solution to the question of the mechanisms of trans-membrane transport is possible only if the specific organization of the lipid-protein system of membranes is clarified and an accurate knowledge of the properties and role of the remaining components of membrane transport systems, i.e. at the structural-biochemical level analysis of the plasma membrane and the entire surface apparatus of the cell.

The limited capabilities of cytophysiological studies of transmembrane transport are clearly demonstrated by the state of the question of the organization of ion channels, which play a major role in many important processes, such as the propagation of a nerve impulse. Using a whole arsenal of various cytophysiological methods, it was shown that in the plasma membrane there are special channels for Na, K, Cl ions, differing in their properties. However, specific knowledge of their structural organization is so far limited to indirect data on their protein nature. Thus, the solution to the question of the organization of ion channels in particular and membrane transport systems in general passes, apparently, into the hands of scientists proficient in structural and biochemical methods, because in this case, numerous and very valuable facts obtained in cytophysiological studies represent represents only the first phenomenological stage in the analysis of these general cellular mechanisms. Nevertheless, in certain aspects of the study of cells, the cytophysiological approach can provide a lot.

Currently, the variety of cytophysiological research techniques is determined both by the ever-increasing arsenal of agents available to cytologists, and by the use of subtle methods for analyzing the changes that occur as a result of the action of these agents on the cell. Previously, to analyze changes in cells under the influence of external agents, methods familiar to physiologists were used, such as recording electrical potentials, assessing cellular respiration by oxygen absorption, quantitative assessment of dye sorption, recording qualitative changes in cell stainability, etc. , then now, for similar purposes, methods characteristic of the structural-functional direction are increasingly used: electron microscopic study of ultrastructural changes, autoradiographic analysis of synthetic processes, etc.

Among the agents used in experimental studies, two main groups can be distinguished. The first group consists of substances whose “point of application” inside the cell is more or less known - these are substances that block individual parts of intracellular metabolism (for example, actinomycin D, which inhibits transcription, or puromycin, which blocks protein synthesis, 2,4-dinitrophenol, which uncouples respiration and oxidative phosphorylation), substances that selectively destroy certain cellular structures (for example, colchicine, which destroys microtubules, or cytochalasin B, which acts on microfibrils). The second group consists of agents of the so-called complex action that change cellular metabolism in general - temperature, osmotic pressure, pH, etc. The use of agents such as, for example, 2,4-dinitrophenol, made it possible to clarify a number of issues concerning the coupling of respiration and phosphorylation in the respiratory chain of mitochondria; the use of RNA and protein synthesis inhibitors has made it possible to study some parts of protein synthesis in ribosomes and transcription processes; with the help of colchicine and cytochalasin, the role of microtubules and microfilaments in the processes of intracellular transport was clarified.

Agents of the second group (complex action) have the advantage that they are more natural for cells, because cells under natural conditions encounter similar changes in the external environment. At the same time, they affect almost all aspects of cellular metabolism, making it difficult to analyze the changes that occur. Nevertheless, the study of the effect of such agents on a cell is of independent importance and is absolutely necessary for studying the mechanisms of cell adaptation to changing environmental factors, resolving the issue of the relationship between specific and nonspecific processes in the reaction of cells to external influences and other similar tasks , playing an important role in the development of the problem of cellular integration.

In the study of the functional organization of cells, the analysis of the mechanisms of interaction between individual cell systems is of great importance. In many cases, this problem can be solved by creating special experimental models. The most typical examples of this kind are nuclear transplants in different objects (protozoa, amphibian eggs); somatic cell hybridization; transplantation of cell parts from protozoa; studies using a number of other microsurgical techniques carried out on protozoological objects and mammalian cells cultured in vitro.

With the help of such models, the most important general cytological issues were studied. For example, the results of experiments on transplanting the nuclei of differentiated amphibian cells into an egg devoid of its own nucleus provided one of the most convincing arguments in favor of the theory of differential gene activity. The essence of the latter is to establish the structural identity of the genomes of differentiated cells of a multicellular organism. From this follows the fundamentally important proposition that the process of differentiation occurs not through irreversible changes in the hereditary apparatus of cells, but through regulation of the activity of a set of genes that is the same for all cells of a given organism.

Very interesting facts were discovered in an experimental model for studying the process of dedifferentiation of a hybrid cell - a chicken erythrocyte and a mammalian cancer cell. The uniqueness of this heterokaryon is that when a chicken erythrocyte fuses with a cancer cell, hemoglobin hemolysis occurs and the normal, almost completely inactivated erythrocyte nucleus ends up in the cytoplasm of the cancer cell. Thus, here a differentiated nucleus is transplanted into unusual conditions of active cytoplasm. Careful observations of changes in the structural organization of these nuclei showed that under new conditions there is a significant increase in their volume. Proteins coming from the cytoplasm play a significant role in nuclear swelling. These external changes in the nuclear apparatus of the erythrocyte reflect deep processes of restructuring of its internal organization, which results in the resumption of transcription of “chicken” messenger RNAs. However, the implementation of the information contained in it in the form of the synthesis of “chicken” proteins does not occur until a nucleolus is formed in the nuclear apparatus of chicken erythrocytes and the synthesis of ribosomal RNA begins. Thus, a thorough analysis of experimental models showed the presence of complex cytoplasmic control over the activity of the nuclear apparatus.

With the help of experimental models, it was possible to solve a number of other important general cytological issues. For example, the question of the mechanisms of movement of anaphase chromosomes was successfully studied on the native mitotic apparatus, isolated from the fragmenting blastomeres of a sea urchin and operating outside the cell. Mainly using experimental models, it was possible to establish a widespread general pattern of cell organization, namely the absence of a strict cause-and-effect principle in the interconnection of complex intracellular processes. It turned out that such multicomponent processes as cell reproduction, processes of synthesis and intracellular transport of high-polymer compounds, etc., consist of separate, relatively autonomous stages, not connected by a strict cause-and-effect relationship. Clarification of this pattern, on the one hand, creates the prerequisites for understanding the mechanisms of the amazing plasticity of cellular organization. On the other hand, this same pattern is the basis for studying the mechanisms of integration of such processes in an entire cellular system under normal conditions.

Currently, the number and variety of experimental models designed to solve certain specific general cytological problems are increasing. This significantly contributes to the progress of our knowledge in a relatively poorly studied area of ​​cytology - the mechanisms of interaction and integration of the work of subcellular systems.

It must be emphasized that the specificity of research carried out within the framework of the experimental approach to the analysis of the patterns of cell organization is an increasingly deepening of the criteria and characteristics by which the analysis of integrating mechanisms and specific functions of individual cellular structures is carried out. At the same time, it becomes clear that successful solution of the problems facing such research is possible only with the widespread introduction into practice of the methods of the structural-functional approach.

The essence of the comparative cytological method of research in general cytology is to clarify the general patterns of cell organization using the entire variety of their varieties provided to the scientist by living nature. The comparative method has two aspects. On the one hand, it is traditionally used to identify related relationships between individual types of cells (especially for single-celled organisms). Based on the phylogenetic systematics of prokaryotic and lower and higher eukaryotic cells created in this way and carried out using subtle cytological criteria, it becomes possible to trace the formation of both individual private cellular systems and general mechanisms of regulation and integration of the cell as an integral system. As an example This kind of application of comparative cytological analysis in cell research can provide interesting data on the fine organization of the nuclear apparatus in prokaryotic, lower and higher eukaryotic cells

The fundamental features of the organization of the nuclear apparatus of eukaryotic cells are the presence of a complex surface apparatus of the nucleus, a significantly larger amount of DNA concentrated in chromosomes compared to prokaryotic cells, and, finally, a unique packaging of DNA using the main proteins - histones Comparative cytological analysis of the nuclear apparatus of lower eukaryotes made it possible to identify among them cells that, in terms of nuclear structure, occupy an intermediate position between pro- and eukaryotic cells. Armored flagellates have a typical surface nuclear apparatus, but their chromosomes, as in the case of prokaryotes, are formed by circular DNA molecules, which are organized into compact structures without the participation of histones, characteristic of all eukaryotes

Recently, in connection with the discovery of fundamental features in the organization of the genome of pro- and eukaryotic cells, comparison of the processes of transcription and RNA maturation in these organisms, as well as in mesokaryotes and cells of lower eukaryotes, has become important. As a result of such comparisons, it is possible that there will be significant changes have been made to our traditional ideas about family relationships in the main groups of organisms and, in particular, the relationships between pro- and eukaryotic cells.

The second example of the traditional application of the evolutionary approach to cytological problems can be attempts to propose a hypothesis for the complication of the mechanisms of equiheritable distribution of chromosomes between daughter cells in the process of evolution, developed on the basis of a comparative analysis of numerous variants of chromosome divergence in protozoa and lower plants. In these cases, nuclear membrane membranes take an active part in the processes of chromosome segregation, which allows for a certain homology with prokaryotic cells, in which the cell membrane plays a leading role in the uniform distribution of sister chromosomes between daughter cells.

Finally, the third example of a traditional evolutionary approach to general cytological problems can be the widespread symbiotic hypothesis of the origin of mitochondria and chloroplasts. Its essence lies in the assumption that these important organelles of energy metabolism arose from prokaryotic organisms that invaded eukaryotic cells at a relatively early stage in the evolution of eukaryotes.

Despite the importance of this kind of general biological constructions for the development of general cytology, the traditional historical approach to the development of general cytological problems is now still of rather limited use. One of the main reasons for this situation is the presence of specific and still insufficiently studied features of the evolutionary process at the cellular and subcellular levels of organization, which makes it extremely difficult to determine related relationships between individual groups of unicellular organisms, and, consequently, to build substantiated evolutionary new hypotheses in the field of general cytology.

Currently, another aspect of the use of the comparative cytological method is more widespread, which does not pursue the goal of directly elucidating the historical conditionality of a particular cellular structure or process. In modern general cytology, this aspect of the use of the comparative method has undergone several modifications.

At the first stage, during the period of introducing fundamentally new morphobiochemical methods into the practice of cytological analysis, the choice of the object of study was determined by the following considerations. Firstly, the convenience of a particular object for the application of the method used was important. Secondly, the degree of expression of this sign in the cell under study played an important role. Thus, to study the general laws of organization of eukaryotic cells, the favorite object was mammalian liver cells with their harmoniously developed system of membrane organelles. Classic works on the analysis of the processes of intracellular transport and secretion maturation were performed on pancreatic cells and mucous goblet cells mammals.

Escherichia coli has been widely used for complex cytological and molecular biological studies of the organization of prokaryotic cells; models for studying the organization of lower eukaryotes were yeast and mold. It turned out that the patterns established in these objects have universal significance, since in many cases they are fundamentally similar in all eukaryotic or all prokaryotic cells. Moreover, a number of patterns of subcellular organization, especially at the molecular and supramolecular levels, turned out to be universal for cells of both pro- and eukaryotic types (organization of membranes, the principle of ribosome structure, etc.), despite the fact that the named cell types are fundamentally different from each other in some respects. This circumstance gave rise to the idea that it is possible to develop basic general cytological problems on a limited range of objects that are convenient from a methodological point of view, and then extend the established patterns to other cells due to their fundamentally similar organization.

However, in recent years, this simplified use of the comparative approach has begun to be criticized as modern cytological methods are introduced into the special biological sciences of the cell - special cytology, protozoology, and botany of lower plants. Morphobiochemical analysis used in these areas of science made it possible to establish facts indicating a huge diversity in the specific implementation of one or another general feature of cell organization, a diversity much greater than followed from the results obtained earlier on “model” objects. This diversity is especially great at the highest subsystemic and systemic levels of cell organization. It is also typical for such complex and multicomponent processes as the processes of intracellular metabolism and transport or the equally hereditary distribution of genetic material during cell division.

The generalization of a large amount of comparative cytological material obtained at the level of modern methodological capabilities forced us to abandon the above-mentioned simplified idea of ​​the role of the comparative method. In this regard, in general cytology (especially in relation to eukaryotic cells), the dominant position is acquired by the idea of ​​​​the need to use a comparative method for the analysis of individual cellular systems or processes that are similar in functional activity in all the diversity of their manifestations in specific cells. With this approach, special intelligibility res is not caused by “typical”, “average” cells, but, on the contrary, by cells that sharply deviate from the average type of organization, cells in which certain characteristics are hypertrophied.

The largest number of such “evading” variants is found among the cells of higher multicellular organisms, where far-reaching specialization of cells within individual tissue systems is developed. Cases of “evasion” from the average type are also widespread among higher protozoa, which have undergone evolution while maintaining a unicellular level of organization. It was during the study of this kind of atypical cells that it was possible to identify a large number of new interesting facts that significantly deepen our understanding of both the general laws of cellular organization and its evolutionary plasticity, which determines the observed diversity of cellular systems. At the same time, as noted above, in the case of special sciences, the greatest interest is caused by the specificity of the manifestation in various objects of common characteristics characteristic of all cells.

In contrast to the special sciences, with a general cytological approach, this question is posed on a slightly different plane, because the researcher seeks to find out how widespread the specific manifestations of a given trait are in different cells, what combination of general mechanisms and what exactly it is caused by. For example, protozoologists managed to discover very interesting dynamics of the formation of the macronucleus after conjugation in gastrociliary ciliates. In the forming macronucleus there is a significant increase in the amount of DNA, and then a sharp reduction of hereditary material is observed (up to 93%). This process of reduction of genetic material also takes place in the somatic cells of a number of groups of multicellular animals (some insects, nematodes). The remaining DNA, small in total quantity, but containing all the information necessary for the functioning of the macronucleus, is replicated many times. As a result, a definitive macronucleus is created, which differs from the micronucleus not only in the amount of DNA, but also in its qualitative composition. The overwhelming majority of non-functioning genes are absent here, while functioning loci are represented by a significant number of copies.

These facts are of great general cytological interest precisely because, as a rule, the phenomena observed here do not simply act as paradoxical signs characteristic only of higher unicellular organisms. Thus, the processes of polytenization, selective replication of individual sections of chromosomal DNA, and, finally, selective reduction of significant sections of the genome - all these phenomena also occur in specialized cells of multicellular organisms. They are probably carried out on the basis of common elementary mechanisms. And the specificity of the complex process of changes in the nuclear apparatus during the formation of the macronucleus in gastrociliary ciliates is mainly due to a peculiar combination of common, universal elementary mechanisms for eukaryotic cells. This kind of idea is now becoming widespread in general cytology. They extremely stimulate targeted comparative cytological studies aimed at elucidating important general cytological problems. Material from the site

An example of a targeted comparative cytological study is the study of the mechanisms of equal distribution of chromosomes during mitosis in eukaryotes by analyzing the mitosis of different species of diatoms: on these objects, in contrast to typical mitoses of metazoan cells, it is possible to clearly morphologically trace the complex changes in microtubule-organizing centers, the formation and mutual divergence of microtubular half-spindles, divergence of chromosomes to the poles of the cell through the formation of a peculiar structure in metaphase - a collar.

In light of the latest data on the leading role of the tubulin-dynein mechanochemical system in the anaphase movement of chromosomes in metazoan cells, it is very likely to assume that this system is also present in diatoms, i.e., here too there is only a peculiar combination of elementary mechanisms common to of all cells and determining mechanochemical processes during mitosis.

Obviously, for the analysis of these mechanisms, the elucidation of which represents one of the very pressing problems of general cytology, it would be promising to have an object where they are clearly differentiated and morphologically expressed.

The number of examples of this kind is constantly growing. This is due, on the one hand, to the ever-expanding introduction of complex modern methods into the practice of particular cytological, protozoological and botanical research, on the other hand, to the accumulation in the comparative cytological studies of facts that are becoming increasingly important for the general cytology and are the focus of its attention. And all this, in turn, leads to the fact that comparative cytological analysis begins to occupy an extremely important place in cytology.

A brief description of the main directions and aspects of modern general cytological research shows that at this stage of the development of cytology there is both a fairly clear delineation of individual directions and their synthesis. The distinction takes place both in methodological terms and in relation to the logic of solving specific problems posed within each of the directions and approaches. The morphofunctional aspect of cytological studies is dominated by a discrete approach to the analysis of cellular structures. One of the most important features of the experimental approach to the study of the patterns of cellular organization is its focus on the analysis of the general integrating mechanisms of the organization of cellular systems and the entire cell. At the same time, as already emphasized above, solving the problems facing such studies is impossible without the widespread use of methods inherent in the morphofunctional approach. Experimental analysis provides a phenomenological characteristic of the properties of certain cellular mechanisms and intracellular processes, thereby creating the necessary basis for the use of a rich arsenal of structural and biochemical methods.

Thus, at the present stage of development of general cytology, there are prerequisites for a very close combination of these two aspects of cytological research. This is natural, since ultimately both approaches pursue the same goal - elucidation of the functional organization of cellular structures and mechanisms of regulation of processes in the entire cellular system.

The comparative cytological approach to the analysis of general cytological problems occupies a special position in modern general cytology. Comparative cytological analysis is carried out on the basis of data obtained on the basis of morphofunctional and experimental approaches, i.e., methodologically, all the main aspects of cytological research are closely related to each other.

The specificity of the comparative cytological approach, the specificity that determines its special position, is the purposeful use of various objects of living nature to study the general patterns of organization of individual cellular structures, intracellular processes and integrating mechanisms in all the diversity of their manifestations in various types of cells.

So, as can be seen from the above, the main directions of cytological research largely determine the specifics of the modern stage of development of general cytology and determine its close relationship with related biological sciences. One of the most characteristic features of this stage is the close relationship of all the most important areas of cytological research in a methodological sense. Moreover, such methodological integration often goes beyond the scope of general cytology.

In cytological work, purely biochemical and molecular biological methods are widely used, and vice versa, in biochemical and molecular biological studies, cytological morphological methods are widely used. The methodological integration of related sciences and the unity of their ultimate goals determined the formation of a new synthetic science of the cell - cell biology. It combines cytology, structural biochemistry, molecular biology, molecular genetics and special biological sciences about the cellular level of organization. Such a combination of related sciences is undoubtedly a progressive phenomenon. However, despite such a synthesis, each of the sciences retains its own methodological specificity and specificity in the formulation and methods of developing problems of cell organization. Currently, the dominant position in this synthetic science belongs to research in molecular biological and molecular genetic directions. This situation is due to the rapid progress of our knowledge about the lower levels of cell organization, but it is only a temporary phenomenon.

In fact, the leading place in the new synthetic science of the cell should be taken by general cytology - the science of the general laws of the cellular level of organization of living matter. Of the modern biological sciences dealing with this level of organization of living matter, general cytology, expanding the targeted comparative cytological approach based on structural and biochemical methods, is most prepared for a deep general biological generalization of the huge factual material on discrete analysis of the - cellular structures in numerous types of cells. General cytology should take a leading position in the analysis of general cellular integrating mechanisms. An important prerequisite for this is the rapid development of new experimental models. Their in-depth analysis using modern methods and the widespread introduction of experimental models into targeted comparative cytological studies should ensure progress in solving one of the main problems of cell organization - the problem of cellular integration.

As factual material accumulates about the elementary universal mechanisms of cell integration and the scope of their modifications, it is general cytology that faces the task of conducting a deep analysis of the historical conditionality of the organization of particular cellular systems and cellular organization in general, as well as the specifics of the evolutionary process on the cellular and subcellular levels of organization of living matter. The solution to this problem is facilitated by the now clearly visible tendency in general cytological studies to combine discrete analysis of individual components of a cell with the study of its kg. to a complete system.

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