Cell- a complex integral physiological system in which all life processes occur: metabolism and energy, irritability, growth, self-reproduction.
Basic elements of a cell - cell membrane , cytoplasm, organelles And core. A cell can live and function normally only in the presence of these components, which closely interact with each other and with the environment. (Fig. 10).
Cell membrane(Fig. 10, 11). Each cell is surrounded by a membrane (approximately 10 nm thick) that separates it from the external environment.
The basis of the membrane is a double layer of fat-like substances ( bilipid). The thickness of this layer of lipids is pierced by protein molecules that form functional openings (pores) in the membrane through which small polar molecules can penetrate into or out of the cell. Some non-polar molecules (for example, organic solvents - alcohols, ethers, acetone) can penetrate into the cell directly through bilipid layer. Large organic and non organic molecules usually do not pass through the membrane. But if necessary, the cell can actively absorb or release them outward, using energy for this.
Since not all molecules freely penetrate the cell membrane, they speak of its selective permeability, which creates its own special chemical composition. By ensuring selectivity of penetration of nutrients into the cell and retaining those harmful to it, the cell membrane performs a protective function and helps maintain the constancy of the internal environment of the cell.
Due to the difference in the permeability of the membrane to the ions of Potassium, Sodium, Chlorine and some other elements, electric charge. Its value, for example, in a nerve cell is only 0.07 V. In this case, the outer surface of the cell membrane is positively charged, and the inner one is negatively charged, which is the basis for the occurrence excitement- an electrical process, which is the first reaction of the cell to the action of a stimulus.
Molecules attach to the outer surface of the membrane receptor proteins, which can perceive various stimuli (chemical, mechanical, electrical). Perceiving the action of the stimulus, the cells change their activity: the nervous cell generates an electrical impulse and transmits it, the muscle cell contracts, and the secretory cell releases secretions. Protein molecules, most often enzyme proteins, are also attached to the inner surface of the membrane.
Cytoplasm- this is the internal content of the cell, consisting of a watery colloidal substance - cytosol And inclusions— insoluble products of cell metabolism. They are drops of fat (for example, in the subcutaneous tissue) or lumps of animal starch glycogen (in the liver or skeletal muscles), which are deposited in the cell for future use. Material from the site
Organelles- these are constantly operating structural components of the cell: mitochondria(provide the process of intracellular respiration - oxidation of carbohydrates, fats and proteins with the release of energy), endoplasmic net With ribosomes, (take part in protein synthesis), apparatus Golgi(accumulates enzymes, hormones), lysosomes(digest substances that are unnecessary for the cell, bacteria, etc.), centrosome(plays significant role in cell division).
Core(Fig. 10) is an essential and largest component of the cell. It contains the bulk of hereditary material molecules of nucleic acids that are assembled into supramolecular structures of the chromosome. There are 23 pairs of chromosomes in the nuclei of human cells. In this case, one chromosome in each pair is maternal, the other is paternal. All cells of the human body have a nucleus, except for mature red blood cells. As a rule, a cell has one nucleus, predominantly spherical in shape.
Structure and functions of cell organelles.
Cell parts and organelles
Structural features
Functions performed
Plasma (cell) membrane.
Educated double layer of lipid molecules (bilayer) and molecules proteins. The membrane is dominated byphospholipids . Proteins are immersed at different depths in the lipid layer or located on the outer or inner surface of the membrane. Attached to some proteins located on the outer surfacecarbohydrates, being a kind of indicators of cell type.Membrane proteins: enzymes; receptors; proteins that form channels (transport of ions into and out of the cell).
Outside the membrane, plant cells havecell wall . Animal cells are covered on the outside of the membraneglycocalyx – a thin layer of proteins and polysaccharides.
1 . Barrier function (protects the cytoplasm from physical and chemical damage).
2 . Metabolism between the cytoplasm and the external environment.
3. Transport of substances : water, ions, inorganic and organic molecules enter the cell from the external environment. Metabolic products and substances synthesized in the cell are released into the external environment. Passive transport (osmosis, diffusion), active transport (phagocytosis, pinocytosis, sodium-potassium pump). Plant cells cannot take up substances by phagocytosis, because... on top of the membrane are covered with a dense layer of fiber.4 Receptor function - membrane receptor proteins transmit signals from outside to the inside of the cell.
5 . Provides communication between cells.
Cytoplasm
Main substance –hyaloplasm (thick colorless colloidal solution): 70-90% water, as well as proteins, lipids and inorganic substances.
In the cytoplasm (in eukaryotes) there is a complex support system -cytoskeleton. Cytoskeleton consists of three elements:
- microtubules (tubulin protein)
- intermediate filaments
- microfilaments ( actin protein)
It is capable of movement - circular, streamy, ciliary.
1 .Metabolic processes in the cell take place in the hyaloplasm.
2 Through it, interaction between the nucleus and organelles occurs.
3 . Cytoskeleton:
- mechanical function (maintains cell shape);
- transport (transfer of various substances, movement of organelles); -participation in the processes of phagocytosis and pinocytosis (microfilaments are capable of changing the shape of the membrane).
Core
1 .The nucleus stores hereditary information about all the characteristics and properties of the cell and the organism as a whole.
2 . The nucleus regulates all metabolic and energy processes.
Nuclear envelope (karyolemma), consisting of two membranes with pores: the inner one is smooth, the outer one goes into the EPS channels.
1 . Separates the nucleus from the cytoplasm.
2 . Regulates the transport of substances from the nucleus to the cytoplasm (i-RNA, t-RNA, ribosomes) and from the cytoplasm to the nucleus (organic substances, ATP)
Nuclear juice, or karyoplasm (semi-liquid substance)
1 .Transport of substances
2 . The environment in which nucleoli and chromatin are located.
Chromatin is DNA bound to proteins. Before a cell divides, the DNA is twisted to form chromosomes. Eachchromosome formed by one DNA molecule in complex with the main protein– histone.
DNA contains the hereditary information of a cell.
Nucleoli- dense round bodies consisting of protein and RNA. Nucleoli are formed on certain regions of chromosomes.
Formation of halves (subunits) of ribosomes from rRNA and protein.
Ribosomes
(non-membrane organelles)
They consist of two subunits - large and small. Each subunit is a complex of rRNA with proteins.
Protein synthesis.
Cell center (non-membrane organelle)
Comprises two centrioles – cylinders located perpendicular to each other.Centriole walls educated nine triplets of microtubules. The main protein that forms centrioles is tubulin.
1 . Participates in the formation of the cytoskeleton.
2 . Plays an important role during cell division (participates in the formation of spindle threads).
Endoplasmic reticulum ER
(single membrane organelle)
A) EPS rough (granular)
B) EPS smooth
Formed by a system of connectedcavities, tubules, tubes.
Ribosomes are located on the membranes.
Membranes are smooth (lacking ribosomes)
Transport system of the cell. Substances synthesized on the membranes of the ER are transported inside the tubes and transported through them to the Golgi apparatus.
Protein synthesis.
Synthesis of carbohydrates and lipids.
In liver cells, EPS is involved in the neutralization of toxic substances, and in muscle cells, calcium ions necessary for muscle contraction accumulate.
Golgi complex (apparatus)
(single membrane organelle)
Discovered in neurons in 1898 by Italian histologist Camillo Golgi. Located next to the EPS. Consists of 3 main components:
- stacks flattened, slightly curved, disc-shapedcavities - “cisterns”
System tubes, extending from cavities;
- bubbles at the ends of the tubes.
1 .Substances accumulate that are used in the cell or released into the external environment.
2 . Formation of lysosomes.
3 . Assembly of cell membranes.
Lysosomes (single membrane organelles)
A small membranous vesicle containing digestiveenzymes(50 species).
1 .Splitting (digestion) of polymers organic compounds, which enter the animal cell during phagocytosis and pinocytosis to monomers assimilated by the cell.
2 . Participation in the removal of dying organs (tail in tadpoles), cells and organelles. During starvation, lysosomes dissolve some organelles, but without killing the cell.
Mitochondria (double-membrane organelles)
Ball, oval or rod-shaped. Covered with outer and inner membranes.The outer membrane is smooth, and the inner forms numerous protrusions, folds -cristas . The inner membrane contains respiratory enzymes and ATP synthesis enzymes. The matrix contains a solution of various enzymes. They have their own genetic system that provides them self-reproduction: DNA, RNA, ribosomes, proteins, lipids, carbohydrates. They can synthesize proteins themselves.
ATP synthesis.
The energy of food substances is converted into ATP energy, which is necessary for the life of the cell and the organism as a whole.
Plastids
(double-membrane organelles).
Characteristic only of plant cells To.
A) Leukoplasts
leukoplasts → chloroplasts (in the light)
chloroplasts → chromoplasts.
B) Chromoplasts
Round shape, colorless.
spherical shape, contain red, yellow, orange pigments.
They serve as a place for storing reserve nutrients (starch grains).
Create big variety colors of flowers (attracting pollinating insects) and plant fruits (distribution of seeds by animals).
B) Chloroplasts (green color)
The shape of biconvex lenses.The outer membrane is smooth, the inner membrane is folded . Outgrowths are formed from its folds -thylakoids ( flat bags). Stacks of thylakoids –grains. Gran membranes contain chlorophyll (green pigment). Each chloroplast contains about 50 grains. In the spaces between grana in the matrix (stroma) there are DNA, RNA, ribosomes. Thus,have their own genetic system that provides them self-reproduction. Protein synthesis by ribosomes.
Thanks to chlorophyll, chloroplasts convert the energy of sunlight into the chemical energy of ATP. ATP is used for the synthesis of organic compounds.
Photosynthesis - the process of formation organic matter(glucose) from inorganic: carbon dioxide and water in the presence of light energy and chlorophyll pigment with the release of oxygen.
Organoids of movement
Eyelashes – numerous cytoplasmic projections on the surface of the membrane.
Removal of dust particles (ciliated epithelium of the upper respiratory tract);
Movement (ciliates – slippers)
Flagella - single cytoplasmic projections on the surface of the membrane.
Movement (spermatozoa, zoospores, single-celled organisms)
Pseudopaedes – amoeboid projections of the cytoplasm.
They are formed in animals in different places of the cytoplasm to capture food and for movement.
Myofibrils – thin filaments up to 1 cm long or more (actin and myosin)
They serve to contract the muscle fibers along which they are located.
Vacuoles.
Characteristic only of plant cells.
Cavities filledcell sap – water with sugars and other organic and inorganic substances. Cell sap may contain pigments that give blue, purple, and crimson colors to petals and other parts of plants, as well as autumn leaves.
1. Maintaining turgor pressure of cells.
2. Accumulation of reserve substances.
3. Coloring of plant organs (attracting pollinating insects, distributing fruits and seeds).
Endoplasmic reticulum:
Structure:
1.system of membrane bags;
2. diameter 25-30 nm;
2.forms a single whole with outer membrane and nuclear membrane;
3.There are 2 types:
rough (granular)
smooth
Functions:
1. protein synthesis (rough type)
2. synthesis of lipids and steroids.
3. transport of synthesized substances.
Golgi complex:
Structure:
1. system of membrane tank bags;
2. bubble system
3.size 20-30 nm
4.located near the core.
Functions:
1. participates in the removal of substances synthesized by the cell (secretion)
2. formation of lysosomes
Ribosomes:
Structure:
1. small organelles - 15-20 nm;
2. consist of 2 subunits
3. contain RNA and protein
4. free or membrane bound
Functions:
protein synthesis on polysomes
Lysosomes:
Structure:
1. spherical membrane bag
2.many hydrolytic enzymes (about 40)
3. size - 1 micron
Functions:
1. digestion of substances
2. splitting of dead parts of the cell
Mitochondria:
Structure:
1. bodies from 0.5 -7 microns
2.surrounded by a membrane
3. internal membrane cristae
4. matrix (ribosomes, DNA, RNA)
5. many enzymes
Functions:
1. oxidation of organic substances
2.ATP synthesis and energy storage
3. synthesis of own proteins
Plasma membrane:
Structure:
1. Thickness - 6-10 nm
2. Liquid mosaic model of the structure:
a) lipid bilayer
b) two layers of proteins that are located on the surface of the lipid layer, immersed in it, and penetrate it through.
Functions:
1. Limits the contents of the cell (protective)
2. Determines selective permeability:
a) diffusion
b) passive transport
c) active transport
3. Phagotocytosis
4. Pinocytosis
5. Provides irritability
6. Provides intercellular contacts
Plastids:
Structure:
1. Size - 3-10 microns
2. there are three types (leukoplasts, chromoplasts, chloroplasts)
3. covered with a protein-lipid membrane
4. stroma-matrix
5. have folds of the inner membrane
6. the stroma contains DNA and ribosomes
7. membranes contain chlorophyll
Functions:
1. Photosynthesis
2. Storage
Core:
Structure:
1. Size - 2-20 microns
2. covered with a protein-lipid membrane
3. karyoplasm - nuclear juice
4. Nucleolus (RNA, protein)
5. Chromatin (DNA, protein)
Functions:
1. DNA storage
2. DNA transcription
Vacuoles:
Structure:
1. large are characteristic of plant cells
2. The sacs are filled with cell sap
3. in animal cells - small:
a) contractile
b) digestive
c) phagotic
Functions:
1. Regulate osmotic pressure in cells
2. They accumulate substances (fruit cell pigments, nutrients, salt)
Cellular center:
Structure:
1. Size - 0.1 - 0.3 microns
2. consists of two centrioles and a centrosphere
3. non-membrane structure
4. contains proteins, carbohydrates, DNA, RNA, lipids
Functions:
1. Forms the cell division spindle, participates in cell division.
2. Participates in the development of flagella and cilia
Cytoplasm:
Structure:
1. Semi-liquid mass of colloidal structure
2. consists of hyaloplasm (proteins, lipids, polysaccharides, RNA, cations, anions)
Functions:
1. Unites cell organelles and ensures their interaction
Cytoskeleton:
Structure:
1. Structure of protein nature - microfilaments (d = 4-7 nm) and microtubules (d = 10-25 nm)
Functions:
1. Support
2. fixation of organelles in a certain position
Permanent cellular structures, cellular organs that ensure the performance of specific functions during the life of the cell - storage and transmission of genetic information, transfer of substances, synthesis and transformation of substances and energy, division, movement, etc.
To the organoids (organelles) of cells eukaryotes relate:
- chromosomes;
- cell membrane;
- mitochondria;
- Golgi complex;
- endoplasmic reticulum;
- ribosomes;
- microtubules;
- microfilaments;
- lysosomes.
Animal cells also contain centrioles and microfibrils, and plant cells contain plastids that are unique to them.
Sometimes the nucleus as a whole is classified as organelles of eukaryotic cells.
Prokaryotes lack most organelles, they have only a cell membrane and ribosomes, which differ from the cytoplasmic ribosomes of eukaryotic cells.
Specialized eukaryotic cells may have complex structures based on universal organelles, such as microtubules and centrioles - the main components of flagella and cilia. Microfibrils underlie tono- and neurofibrils. Special structures of unicellular organisms, such as flagella and cilia (constructed in the same way as in multicellular cells), perform the function of organs of movement.
More often in modern literature terms " organoids " And " organelles " are used as synonyms.
Structures common to animal and plant cells
| Schematic illustration | Structure | Functions |
|
| Plasma membrane (plasmalemma, cell membrane) | Two layers of lipid (bilayer) between two layers of protein | A selectively permeable barrier that regulates the exchange between the cell and the environment |
|
| Core | The largest organelle, enclosed in a shell of two membranes, permeated nuclear pores. Contains chromatin- in this form, unwound chromosomes are in interphase. Also contains a structure called nucleolus | Chromosomes contain DNA - the substance of heredity. DNA consists of genes that regulate all types of cellular activity. Nuclear division underlies cell reproduction, and therefore the reproduction process. Ribosomes are formed in the nucleolus |
|
| Endoplasmic reticulum (ER) | System of flattened membrane bags - tanks- in the form of tubes and plates. Forms a single unit with the outer membrane of the nuclear envelope | If the surface of the ER is covered with ribosomes, then it is called rough.Protein synthesized on ribosomes is transported through the tanks of such an ER. Smooth ER(without ribosomes) serves as a site for the synthesis of lipids and steroids |
|
| Ribosomes | Very small organelles consisting of two subparticles - large and small. They contain protein and RNA in approximately equal proportions. Ribosomes, found in mitochondria (and also in chloroplasts in plants), are even smaller | The site of protein synthesis, where various interacting molecules are held in the correct position. Ribosomes are associated with the ER or lie free in the cytoplasm. Many ribosomes can form polysome (polyribosome), in which they are strung on a single strand of messenger RNA |
|
| Mitochondria | The mitochondrion is surrounded by a shell of two membranes, the inner membrane forms folds ( cristas). Contains a matrix containing a small number of ribosomes, one circular DNA molecule and phosphate granules | During aerobic respiration, oxidative phosphorylation and electron transfer occur in the cristae, and enzymes involved in the Krebs cycle and the oxidation of fatty acids operate in the matrix. |
|
| Golgi apparatus | A stack of flattened membrane sacs - tanks. At one end, stacks of pouches are continuously formed, and at the other, they are laced up in the form of bubbles. Stacks can exist as discrete dictyosomes, as in plant cells, or form a spatial network, as in many animal cells | Many cellular materials, such as enzymes from the ER, undergo modification in cisternae and are transported in vesicles. The Golgi apparatus is involved in the process of secretion, and lysosomes are formed in it |
|
| Lysosomes | A simple spherical membrane sac (single membrane) filled with digestive (hydrolytic) enzymes. Content appears homogeneous | Perform many functions, always associated with the disintegration of any structures or molecules |
|
| Microbodies | The organelle is not quite regular spherical in shape, surrounded by a single membrane. The contents have a granular structure, but sometimes there is a crystalloid, or a collection of threads, in it | All microbodies contain catalase, an enzyme that catalyzes the breakdown of hydrogen peroxide. All of them are associated with oxidative reactions |
|
| Cell wall, median lamina, plasmodesmata |
|||
| cell wall | Rigid cell wall surrounding the cell, consists of cellulose microfibrils immersed in a matrix that includes other complex polysaccharides, namely hemicelluloses and pectins. In some cells, the cell walls undergo secondary thickening | Provides mechanical support and protection. Thanks to it, turgor pressure arises, which enhances the support function. Prevents osmotic cell rupture. The movement of water and mineral salts occurs along the cell wall. Various modifications, such as lignin impregnation, provide specialized functions |
|
| middle plate | A thin layer of pectin substances (calcium and magnesium pectates) | Holds cells together |
|
| plasmodesma | A thin cytoplasmic filament that links the cytoplasm of two adjacent cells through a thin pore in the cell wall. The pore is lined with a plasma membrane. The desmotubule passes through the pore, often connected at both ends to the ER | Unite protoplasts of neighboring cells into a single continuous system - simplast, through which substances are transported between these cells |
|
| Chloroplast | A large, chlorophyll-containing plastid in which photosynthesis occurs. The chloroplast is surrounded by a double membrane and filled with gelatinous stroma. The stroma contains a system of membranes assembled into stacks, or grains. Starch can also be deposited in it. In addition, the stroma contains ribosomes, a circular DNA molecule and oil droplets | Photosynthesis occurs in this organelle, that is, the synthesis of sugars and other substances from CO 2 and water due to light energy captured by chlorophyll. Light energy is converted into chemical energy |
|
| Large central vacuole | A sac formed by a single membrane called tonoplast. The vacuole contains cell sap- a concentrated solution of various substances, such as mineral salts, sugars, pigments, organic acids and enzymes. In mature cells, vacuoles are usually large | Various substances are stored here, including the end products of metabolism. The osmotic properties of the cell strongly depend on the contents of the vacuole. Sometimes the vacuole functions as a lysosome |
|
Comparative characteristics of RNA and DNA
| Signs | RNA | DNA |
| Location in the cage | Nucleus, ribosomes, cytoplasm, mitochondria, chloroplasts | Nucleus, mitochondria, chloroplasts |
| Location in the nucleus | Nucleolus | Chromosomes |
| Structure of a macromolecule | Single polynucleotide chain | Double unbranched linear polymer, coiled in a right-handed helix |
| Monomers | Ribonucleotides | Deoxyribonucleotides |
| Nucleotide composition | Nitrogen base (purine - adenine, guanine, pyrimidine - uracil, cytosine); ribose (carbohydrate): phosphoric acid residue | Nitrogen base (purine - adenine, guanine, pyrimidine - thymine, cytosine); deoxyribose (carbohydrate): phosphoric acid residue |
| Types of Nucleotides | Alenyl (A), guanyl (G), uridyl (U), cytidyl (C) | Alenyl (A), guanyl (G), thymidyl (T), cytidyl (C) |
| Properties | Incapable of self-doubling. Labilna | Capable of self-duplication according to the principle of complementarity (reduplication): A-T, T-A, G-C, C-G Stable |
| Functions | Informational (mRNA) - transmits the code of hereditary information about the primary structure of the protein molecule; ribosomal (rRNA) - part of ribosomes; transport (tRNA) - transfers amino acids to ribosomes; mitochondrial and plastid RNA - are part of the ribosomes of these organelles | Chemical basis of chromosomal genetic material (gene); DNA synthesis, RNA synthesis, protein structure information |