Eukaryotic cell, main structural components, their structure and functions: organelles, cytoplasm, inclusions. Prokaryotic and eukaryotic cells Functions of eukaryotic organisms

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Cell- a complex system consisting of three structural and functional subsystems of the surface apparatus, the cytoplasm with organelles and the nucleus.

eukaryotes(nuclear) - cells that, unlike prokaryotes, have a formed cell nucleus, limited from the cytoplasm by the nuclear membrane.

Eukaryotic cells include animal, human, plant, and fungal cells.

The structure of eukaryotic cells

Autolysis(autolysis) - self-dissolution of living cells and tissues under the action of their own hydrolytic enzymes that destroy structural molecules. Occurs in the body during physiological processes: metamorphosis, autotomy, also after death.

Xanthophyll- a plant pigment that gives yellow and brown colors to parts of plants (yellow leaves, red carrots, tomatoes). Belongs to the group of carotenoids.

Carotenoids- a group of plant pigments - high molecular weight hydrocarbons. They accumulate in chloroplasts and, mainly, in chromoplasts. This group includes carotenes and xanthophylls; of the latter, zeaxanthin, capxanthin, xanthine, lycopene, and lutein are the most common. Participate in the process of photosynthesis, absorbing the energy of the blue part of the solar spectrum; color flowers, fruits, seeds, root crops, and in autumn - leaves.

Tissue turgor- internal hydrostatic pressure in a living cell, causing tension in the cell membrane.

Mitotic spindle(spindle) - a structure that occurs in eukaryotic cells during nuclear division (mitosis). It got its name for the distant resemblance of the shape to the spindle.

cytoskeleton- the cell frame or skeleton located in the cytoplasm of a living cell. It is present in all cells in both eukaryotes and prokaryotes. Made up of microtubules and microfilaments. Maintains the shape and movement of the cell.

Phagocytosis- a process in which blood and tissue cells (phagocytes) capture and digest pathogens of infectious diseases and dead cells.

Phagocytes are the common name for cells: in the blood - granular leukocytes (granulocytes), in tissues - macrophages. The process was discovered by I.I. Mechnikov in 1882.

Phagocytosis is one of the protective reactions of the body.

pinocytosis- 1. capture by the cell surface of the liquid with the substances contained in it. 2. the process of absorption and intracellular destruction of macromolecules. One of the main mechanisms for the penetration of macromolecular compounds into the cell, in particular proteins and carbohydrate-protein complexes.

Used Books:

1. Biology: a complete guide to preparing for the exam. / G.I. Lerner. - M.: AST: Astrel; Vladimir; VKT, 2009

2. Biology: textbook. for students in grade 11 general education. Institutions: Basic level / Ed. prof. I.N. Ponomareva. - 2nd ed., revised. - M.: Ventana-Graf, 2008.

3. Biology for applicants to universities. Intensive course / G.L. Bilich, V.A. Kryzhanovsky. - M.: Onyx Publishing House, 2006.

4. General biology: textbook. for 11 cells. general education institutions / V.B. Zakharov, S.G. Sonin. - 2nd ed., stereotype. - M.: Bustard, 2006.

5. Biology. General biology. Grades 10-11: textbook. for general education institutions: basic level / D.K. Belyaev, P.M. Borodin, N.N. Vorontsov and others, ed. D.K.Belyaeva, G.M.Dymshits; Ros. acad. Sciences, Ros. acad. education, publishing house "Enlightenment". - 9th ed. - M.: Education, 2010.

6. Biology: study guide / A.G. Lebedev. M.: AST: Astrel. 2009.

7. Biology. Full course of secondary school: textbook for schoolchildren and applicants / M.A.Valovaya, N.A.Sokolova, A.A. Kamensky. - M.: Exam, 2002.

Used Internet resources:

Wikipedia. Cell structure

Characterization of eukaryotic cells

The average size of a eukaryotic cell is about 13 microns. The cell is divided by internal membranes into different compartments (reaction spaces). Three types of organelles clearly separated from the rest of the protoplasm (cytoplasm) by a shell of two membranes: the cell nucleus, mitochondria and plastids. Plastids serve mainly for photosynthesis, and mitochondria for energy production. All layers contain DNA as a carrier of genetic information.

Cytoplasm contains various organelles, including ribosomes, which are also found in plastids and mitochondria. All organelles lie in the matrix.

Characterization of prokaryotic cells

The average size of prokaryotic cells is 5 microns. They do not have any internal membranes other than protrusions of the internal membranes and the plasma membrane. Instead of a cell nucleus, there is a nucleoid, devoid of a shell and consisting of a single DNA molecule. In addition, bacteria can contain DNA in the form of tiny plasmids similar to eukaryotic extranuclear DNA.

IN prokaryotic cells, capable of photosynthesis (blue-green algae, green and purple bacteria), there are variously structured large protrusions of the membrane - thylakoids, in their function corresponding to eukaryotic plastids. Prokaryotes are characterized by the presence of a moray sac - a mechanically strong element of the cell wall.

The main components of a eukaryotic cell. Their structure and functions.

Shell necessarily contains a plasma membrane. In addition to it, plants and fungi have a cell wall, and animals have a glycocalyx.

Plants and fungi secrete protoplast- all the contents of the cell, except for the cell wall.

Cytoplasm is the internal semi-liquid environment of the cell. Consists of hyaloplasm, inclusions and organelles. In the cytoplasm, exoplasm is isolated (the cortical layer lies directly under the membrane, does not contain organelles) and endoplasm (the inner part of the cytoplasm).

Hyaloplasm(cytosol) is the main substance of the cytoplasm, a colloidal solution of large organic molecules. Provides the relationship of all components of the cell

In it, the main metabolic processes, for example, glycolysis, take place.

Inclusions are optional components of the cell that can appear and disappear depending on the state of the cell. For example: drops of fat, starch granules, protein grains.

Organelles There are membrane and non-membrane.

Membrane organelles are single-membrane (EPS, AG, lysosomes, vacuoles) and double membrane(plastids, mitochondria).

TO non-membrane organelles include ribosomes and a cell center.

Organelles of eukaryotic cells, their structure and functions.

Endoplasmic reticulum- single-membrane organelle. It is a system of membranes that form "tanks" and channels, connected to each other and limiting a single internal space - EPS cavities. There are two types of EPS: 1) rough, containing ribosomes on its surface, and 2) smooth, the membranes of which do not carry ribosomes.

Functions: 1) transport of substances from one part of the cell to another, 2) division of the cytoplasm of the cell into compartments (“compartments”), 3) synthesis of carbohydrates and lipids (smooth ER), 4) protein synthesis (rough ER)

golgi apparatus- single-membrane organelle. It is a stack of flattened "tanks" with widened edges. A system of small single-membrane vesicles (Golgi vesicles) is associated with them. Each stack usually consists of 4-6 "tanks", is a structural and functional unit of the Golgi apparatus and is called a dictyosome.

Functions of the Golgi apparatus: 1) accumulation of proteins, lipids, carbohydrates, 2) “packaging” of proteins, lipids, carbohydrates into membrane vesicles, 4) secretion of proteins, lipids, carbohydrates, 5) synthesis of carbohydrates and lipids, 6) site of formation of lysosomes.

Lysosomes- single-membrane organelles. They are small vesicles containing a set of hydrolytic enzymes. Enzymes are synthesized on the rough ER, move to the Golgi apparatus, where they are modified and packaged into membrane vesicles, which, after separation from the Golgi apparatus, become lysosomes proper. The breakdown of substances by enzymes is called lysis.

Functions of lysosomes: 1) intracellular digestion of organic substances, 2) destruction of unnecessary cellular and non-cellular structures, 3) participation in the processes of cell reorganization.

Vacuoles- single-membrane organelles are "tanks" filled with aqueous solutions of organic and inorganic substances. The liquid that fills the plant vacuole is called cell sap.

Vacuole functions: 1) accumulation and storage of water, 2) regulation of water-salt metabolism, 3) maintenance of turgor pressure, 4) accumulation of water-soluble metabolites, reserve nutrients, 5) coloring of flowers and fruits and thereby attracting pollinators and seed dispersers

Mitochondria bounded by two membranes. The outer membrane of mitochondria is smooth, the inner one forms numerous folds - cristae. Cristae increase the surface area of ​​the inner membrane, which hosts multienzyme systems involved in the synthesis of ATP molecules. The inner space of mitochondria is filled with matrix. The matrix contains circular DNA, specific mRNA, prokaryotic-type ribosomes, Krebs cycle enzymes.

Mitochondrial functions: 1) ATP synthesis, 2) oxygen breakdown of organic substances.

plastids characteristic only of plant cells. There are three main types of plastids: leukoplasts - colorless plastids in the cells of unpainted parts of plants, chromoplasts - colored plastids, usually yellow, red and orange, chloroplasts - green plastids.

Chloroplasts. In the cells of higher plants, chloroplasts have the shape of a biconvex lens. Chloroplasts are bounded by two membranes. The outer membrane is smooth, the inner one has a complex folded structure. The smallest fold is called the thylakoid. A group of thylakoids stacked like a stack of coins is called a grana. The thylakoid membranes contain photosynthetic pigments and enzymes that provide ATP synthesis. The main photosynthetic pigment is chlorophyll, which determines the green color of chloroplasts.

The inner space of chloroplasts is filled stroma. The stroma contains circular DNA, ribosomes, enzymes of the Calvin cycle, starch grains.

Function of chloroplasts: photosynthesis.

The function of leukoplasts: synthesis, accumulation and storage of reserve nutrients.

Chromoplasts. The stroma contains circular DNA and pigments - carotenoids, which give the chromoplasts a yellow, red or orange color.

Function of chromoplasts: coloring of flowers and fruits and thereby attracting pollinators and seed dispersers.

Ribosomes- non-membrane organelles, about 20 nm in diameter. Ribosomes are made up of two subunits, large and small. The chemical composition of ribosomes - proteins and rRNA. rRNA molecules make up 50–63% of the mass of the ribosome and form its structural framework. During protein biosynthesis, ribosomes can "work" singly or combine into complexes - polyribosomes (polysomes ) . In such complexes, they are linked to each other by a single mRNA molecule. The association of subunits into a whole ribosome occurs in the cytoplasm, as a rule, during protein biosynthesis.

Ribosome function: assembly of the polypeptide chain (protein synthesis).

cytoskeleton made up of microtubules and microfilaments. Microtubules are cylindrical unbranched structures. The main chemical component is the protein tubulin. Microtubules are destroyed by colchicine. Microfilaments are filaments made up of the protein actin. Microtubules and microfilaments form complex tangles in the cytoplasm.

Functions of the cytoskeleton: 1) determination of the shape of the cell, 2) support for organelles, 3) formation of a division spindle, 4) participation in cell movements, 5) organization of the cytoplasmic flow.

Cell Center It contains two centrioles and a centrosphere. The centriole is a cylinder, the wall of which is formed by nine groups of three fused microtubules. Centrioles are paired, where they are located at right angles to each other. Before cell division, centrioles diverge to opposite poles, and a daughter centriole appears near each of them. They form a spindle of division, which contributes to the uniform distribution of genetic material between daughter cells.

Functions: 1) ensuring the divergence of chromosomes to the poles of the cell during mitosis or meiosis, 2) the center of organization of the cytoskeleton.

eukaryotic cells from the simplest organisms to the cells of higher plants and mammals, differ in complexity and diversity of structure. typical eukaryotic cell does not exist, but common features can be distinguished from thousands of cell types. Each eukaryotic cell consists of cytoplasm and nucleus.

Structure eukaryotic cell.

plasmalemma(cell wall) of animal cells is formed by a membrane covered on the outside with a layer of glycocalyx 10-20 nm thick. plasmalemma performs delimiting, barrier, transport and receptor functions. Due to the property of selective permeability, the plasmalemma regulates the chemical composition of the internal environment of the cell. The plasmalemma contains receptor molecules that selectively recognize certain biologically active substances (hormones). In layers and layers, neighboring cells are retained due to the presence of various types of contacts, which are represented by sections of the plasmalemma that have a special structure. From the inside, the cortical (cortical) layer adjoins the membrane cytoplasm 0.1-0.5 µm thick.

Cytoplasm. In the cytoplasm there is a number of formalized structures that have regular features of the structure and behavior in different periods of the cell's life. Each of these structures has a specific function. From this arose their comparison with the organs of the whole organism, in connection with which they received the name organelles, or organelles. Various substances are deposited in the cytoplasm - inclusions (glycogen, fat drops, pigments). The cytoplasm is permeated with membranes endoplasmic reticulum.

Endoplasmic Reticulum (EMF). The endoplasmic reticulum is a branched network of channels and cavities in the cytoplasm of a cell, formed by membranes. On the membranes of the channels there are numerous enzymes that ensure the vital activity of the cell. There are 2 types of EMF membranes - smooth and rough. On membranes smooth endoplasmic reticulum there are enzyme systems involved in fat and carbohydrate metabolism. main function rough endoplasmic reticulum- protein synthesis, which is carried out in ribosomes attached to membranes. Endoplasmic reticulum- this is a common intracellular circulatory system, through the channels of which substances are transported inside the cell and from cell to cell.

Ribosomes carry out the function of protein synthesis. Ribosomes are spherical particles with a diameter of 15-35 nm, consisting of 2 subunits of unequal sizes and containing approximately equal amounts of proteins and RNA. Ribosomes in the cytoplasm are located or attached to the outer surface of the membranes of the endoplasmic reticulum. Depending on the type of protein synthesized, ribosomes can be combined into complexes - polyribosomes. Ribosomes are present in all cell types.

Golgi complex. The main structural element Golgi complex is a smooth membrane that forms packs of flattened cisterns, or large vacuoles, or small vesicles. The cisterns of the Golgi complex are connected to the channels of the endoplasmic reticulum. Proteins, polysaccharides, fats synthesized on the membranes of the endoplasmic reticulum are transported to the complex, condensed inside its structures and "packed" in the form of a secret ready for release, or used in the cell itself during its life.

Mitochondria. The general distribution of mitochondria in the animal and plant world indicates the important role that mitochondria play in a cage. Mitochondria have the form of spherical, oval and cylindrical bodies, they can be filamentous. The size of mitochondria is 0.2-1 µm in diameter, up to 5-7 µm in length. The length of filamentous forms reaches 15-20 microns. The number of mitochondria in the cells of different tissues is not the same, there are more of them where synthetic processes are intensive (liver) or energy costs are high. The wall of mitochondria consists of 2 membranes - outer and inner. The outer membrane is smooth, and partitions - ridges, or cristae, depart from the inner inside of the organoid. On the membranes of the cristae are numerous enzymes involved in energy metabolism. The main function of mitochondria - ATP synthesis.

Lysosomes- small oval bodies with a diameter of about 0.4 microns, surrounded by one three-layer membrane. Lysosomes contain about 30 enzymes capable of breaking down proteins, nucleic acids, polysaccharides, lipids, and other substances. The breakdown of substances by enzymes is called lysis, therefore the organoid is named lysosome. It is believed that lysosomes are formed from the structures of the Golgi complex or directly from the endoplasmic reticulum. Functions of lysosomes : intracellular digestion of nutrients, destruction of the structure of the cell itself during its death during embryonic development, when the embryonic tissues are replaced by permanent ones, and in a number of other cases.

Centrioles. The cell center consists of 2 very small cylindrical bodies located at right angles to each other. These bodies are called centrioles. The centriole wall consists of 9 pairs of microtubules. Centrioles are capable of self-assembly and are self-reproducing organelles of the cytoplasm. Centrioles play an important role in cell division: they begin the growth of microtubules that form the spindle of division.

Core. The nucleus is the most important component of the cell. It contains DNA molecules and therefore performs two main functions: 1) storage and reproduction of genetic information, 2) regulation of metabolic processes occurring in the cell. Cell that has lost core, cannot exist. The nucleus is also incapable of independent existence. Most cells have one nucleus, but 2-3 nuclei can be observed in one cell, for example, in liver cells. Known multinucleated cells with the number of nuclei in a few tens. The shape of the nuclei depends on the shape of the cell. The nuclei are spherical, multi-lobed. The nucleus is surrounded by a membrane consisting of two membranes having the usual three-layer structure. The outer nuclear membrane is covered with ribosomes, the inner membrane is smooth. The main role in the vital activity of the nucleus is played by the metabolism between the nucleus and the cytoplasm. The contents of the nucleus include nuclear juice, or karyoplasm, chromatin and nucleolus. The composition of the nuclear juice includes various proteins, including most of the nuclear enzymes, free nucleotides, amino acids, products of the nucleolus and chromatin, moving from the nucleus to the cytoplasm. Chromatin contains DNA, proteins and is a spiralized and compacted sections of chromosomes. nucleolus is a dense rounded body located in the nuclear juice. The number of nucleoli varies from 1 to 5-7 or more. There are nucleoli only in non-dividing nuclei, during mitosis they disappear, and after division is completed, they are formed again. The nucleolus is not an independent cell organelle; it is devoid of a membrane and is formed around the chromosome region in which the rRNA structure is encoded. Ribosomes are formed in the nucleolus, which then move to the cytoplasm. chromatin called lumps, granules and network-like structures of the nucleus, intensely stained with some dyes and different in shape from the nucleolus.

In most cases, eukaryotic cells are part of multicellular organisms. However, in nature there is a considerable number of unicellular eukaryotes, which are structurally a cell, and physiologically - a whole organism. In turn, eukaryotic cells, which are part of a multicellular organism, are not capable of independent existence. They are usually divided into cells of plants, animals and fungi. Each of them has its own characteristics and has its own subtypes of cells that form different tissues.

Despite the diversity, all eukaryotes have a common ancestor, presumably appeared in the process.

In the cells of unicellular eukaryotes (protozoa) there are structural formations that perform the functions of organs at the cellular level. So ciliates have a cellular mouth and pharynx, powder, digestive and contractile vacuoles.

All eukaryotic cells are isolated, delimited from the external environment. In the cytoplasm there are various cell organelles already delimited from it by their membranes. The nucleus contains the nucleolus, chromatin, and nuclear juice. Numerous (larger than in prokaryotes) various inclusions are present in the cytoplasm.

Eukaryotic cells are characterized by a high orderliness of the internal contents. Such compartmentation achieved by dividing the cell into parts by membranes. Thus, the separation of biochemical processes is achieved in the cell. The molecular composition of membranes, the set of substances and ions on their surface is different, which determines their functional specialization.

In the cytoplasm there are proteins-enzymes of glycolysis, sugar metabolism, nitrogenous bases, amino acids and lipids. Microtubules are assembled from certain proteins. The cytoplasm performs unifying and framework functions.

Inclusions are relatively unstable components of the cytoplasm, which are nutrient reserves, secretion granules (products for removal from the cell), ballast (a number of pigments).

Organelles are permanent and perform vital functions. Among them there are organelles of general importance (, ribosomes, polysomes, microfibrils and, centrioles, and others) and special in specialized cells (microvilli, cilia, synaptic vesicles, etc.).

The structure of an animal eukaryotic cell

Eukaryotic cells are capable of endocytosis (uptake of nutrients by the cytoplasmic membrane).

Eukaryotes (if any) are of a different chemical nature than prokaryotes. In the latter, it is based on murein. In plants, it is mainly cellulose, and in fungi, it is chitin.

The genetic material of eukaryotes is contained in the nucleus and is packaged in chromosomes, which are a complex of DNA and proteins (mainly histones).

Eukaryotes include the kingdoms of plants, animals, and fungi.

The main features of eukaryotes.

1. The cell is divided into cytoplasm and nucleus.
2. Most of the DNA is concentrated in the nucleus. It is nuclear DNA that is responsible for most of the life processes of the cell and for the transmission of heredity to daughter cells.
3. Nuclear DNA is dissected into strands that are not closed into rings.
4. DNA strands are linearly elongated inside the chromosomes, clearly visible during mitosis. The set of chromosomes in the nuclei of somatic cells is diploid.
5. The system of external and internal membranes is developed. Internal divide the cell into separate compartments - compartments. They take part in the formation of cell organelles.
6. There are many organelles. Some organelles are surrounded by a double membrane: nucleus, mitochondria, chloroplasts. In the nucleus, along with the membrane and nuclear juice, the nucleolus and chromosomes are found. The cytoplasm is represented by the main substance (matrix, hyaloplasm) in which inclusions and organelles are distributed.
7. A large number of organelles are limited to a single membrane (lysosomes, vacuoles, etc.)
8. In a eukaryotic cell, organelles of general and special significance are distinguished. For example: general meaning - nucleus, mitochondria, ER, etc.; of special importance - microvilli of the suction surface of the epithelial cells of the intestine, cilia of the epithelium of the trachea and bronchi.
9. Mitosis is a characteristic mechanism of reproduction in generations of genetically similar cells.
10. The sexual process is characteristic. True sex cells are formed - gametes.
11. Not capable of fixing free nitrogen.
12. Aerobic respiration occurs in mitochondria.
13. Photosynthesis takes place in chloroplasts containing membranes, which are usually arranged in grana.
14. Eukaryotes are represented by unicellular, filamentous and truly multicellular forms.

The main structural components of a eukaryotic cell

organelles

Core. Structure and functions.

The cell has a nucleus and cytoplasm. cell nucleus consists of a membrane, nuclear juice, nucleolus and chromatin. Functional role nuclear envelope consists in the separation of the genetic material (chromosomes) of the eukaryotic cell from the cytoplasm with its numerous metabolic reactions, as well as the regulation of bilateral interactions between the nucleus and the cytoplasm. The nuclear envelope consists of two membranes separated by a perinuclear (perinuclear) space. The latter can communicate with the tubules of the cytoplasmic reticulum.

The nuclear envelope is pierced by a sill with a diameter of 80-90nm. The pore region or pore complex with a diameter of about 120 nm has a certain structure, which indicates a complex mechanism for the regulation of nuclear-cytoplasmic movements of substances and structures. The number of pores depends on the functional state of the cell. The higher the synthetic activity in the cell, the greater their number. It is estimated that in lower vertebrates in erythroblasts, where hemoglobin is intensively formed and accumulated, there are about 30 pores per 1 μm 2 of the nuclear membrane. In mature erythrocytes of these animals that retain nuclei, up to five pores remain per 1 μg of the membrane, i.e. 6 times less.

In the region of the feather complex, the so-called dense plate - a protein layer that underlies the entire length of the inner membrane of the nuclear membrane. This structure primarily performs a supporting function, since in its presence the shape of the nucleus is preserved even if both membranes of the nuclear envelope are destroyed. It is also assumed that the regular connection with the substance of the dense plate contributes to the ordered arrangement of chromosomes in the interphase nucleus.

basis nuclear juice, or matrix, make up proteins. Nuclear juice forms the internal environment of the nucleus, and therefore it plays an important role in ensuring the normal functioning of the genetic material. The composition of nuclear juice contains filamentous, or fibrillar, proteins, with which the implementation of the support function is associated: the matrix also contains the primary products of transcription of genetic information - heteronuclear RNA (hnRNA), which are processed here, turning into mRNA (see 3.4.3.2).

nucleolus is the structure in which formation and maturation take place ribosomal RNA (rRNA). rRNA genes occupy certain areas (depending on the type of animal) of one or more chromosomes (in humans, 13-15 and 21-22 pairs) - nucleolar organizers, in the area of ​​\u200b\u200bwhich the nucleoli are formed. Such regions in metaphase chromosomes look like constrictions and are called secondary stretches. WITH Using an electron microscope, filamentous and granular components are revealed in the nucleolus. The filamentous (fibrillar) component is represented by complexes of protein and giant RNA precursor molecules, from which smaller molecules of mature rRNA are then formed. In the process of maturation, fibrils are transformed into ribonucleoprotein grains (granules), which represent the granular component.

Chromatin structures in the form of lumps, scattered in the nucleoplasm, are an interphase form of the existence of cell chromosomes

cytoplasm

IN cytoplasm distinguish between the main substance (matrix, hyaloplasm), inclusions and organelles. The main substance of the cytoplasm fills the space between the plasmalemma, nuclear membrane and other intracellular structures. An ordinary electron microscope does not reveal any internal organization in it. The protein composition of the hyaloplasm is diverse. The most important of the proteins are represented by enzymes of haicolysis, metabolism of sugars, nitrogenous bases, amino acids and lipids. A number of hyaloplasmic proteins serve as subunits from which structures such as microtubules are assembled.

The main substance of the cytoplasm forms the true internal environment of the cell, which unites all intracellular structures and ensures their interaction with each other. The fulfillment of the unifying and scaffolding functions by the matrix can be associated with the microtrabecular network detected using a super-powerful electron microscope, formed by thin fibrils 2–3 nm thick and penetrating the entire cytoplasm. Through the hyaloplasm, a significant amount of intracellular movements of substances and structures is carried out. The main substance of the cytoplasm should be considered in the same way as a complex colloidal system capable of moving from a sol-like (liquid) state to a gel-like one. In the process of such transitions, work is done. For the functional significance of such transitions, see Sec. 2.3.8.

inclusions(Fig. 2.5) are called relatively unstable components of the cytoplasm, which serve as reserve nutrients (fat, glycogen), products to be removed from the cell (secret granules), ballast substances (some pigments).

Organelles - These are permanent structures of the cytoplasm that perform vital functions in the cell.

Isolate organelles general meaning And special. The latter are present in a significant amount in cells specialized to perform a certain function, but in a small amount they can also be found in other types of cells. These include, for example, microvilli of the suction surface of the intestinal epithelial cell, cilia of the epithelium of the trachea and bronchi, synaptic vesicles that transport substances that carry nerve excitation from one nerve cell to another or a cell of the working organ, myofibrils, on which muscle contraction depends. A detailed consideration of special organelles is included in the task of the course of histology.

Organelles of general importance include elements of the tubular and vacuolar system in the form of a rough and smooth cytoplasmic reticulum, a lamellar complex, mitochondria, ribosomes and polysomes, lysosomes, peroxisomes, microfibrils and microtubules, centrioles of the cell center. Chloroplasts are also isolated in plant cells, in which photosynthesis takes place.

tubular And vacuolar system formed by communicating or separate tubular or flattened (cistern) cavities, limited by membranes and spreading throughout the cytoplasm of the cell. Often, tanks have bubble-like extensions. In this system, there are rough And smooth cytoplasmic reticulum(see Fig. 2.3). A feature of the structure of a rough network is that polysomes are attached to its membranes. Because of this, it performs the function of synthesizing a certain category of proteins that are mainly removed from the cell, for example, secreted by gland cells. In the area of ​​the rough network, the formation of proteins and lipids of cytoplasmic membranes, as well as their assembly. Densely packed into a layered structure, cisterns of a rough network are the sites of the most active protein synthesis and are called ergastoplasm.

The membranes of the smooth cytoplasmic reticulum are devoid of polysomes. Functionally, this network is associated with the metabolism of carbohydrates, fats and other non-protein substances, such as steroid hormones (in the gonads, adrenal cortex). Through the tubules and cisterns, substances move, in particular, the material secreted by the glandular cell, from the site of synthesis to the packing area into granules. In areas of liver cells rich in smooth network structures, harmful toxic substances and some drugs (barbiturates) are destroyed and rendered harmless. In the vesicles and tubules of the smooth network of striated muscles, calcium ions are stored (deposited), which play an important role in the contraction process.

Ribosome - it is a rounded ribonucleoprotein particle with a diameter of 20-30nm. It consists of small and large subunits, the combination of which occurs in the presence of messenger (messenger) RNA (mRNA). One mRNA molecule usually combines several ribosomes like a string of beads. Such a structure is called polysome. Polysomes are freely located in the ground substance of the cytoplasm or attached to the membranes of the rough cytoplasmic reticulum. In both cases, they serve as a site for active protein synthesis. Comparison of the ratio of the number of free and membrane-attached polysomes in embryonic undifferentiated and tumor cells, on the one hand, and in specialized cells of an adult organism, on the other hand, led to the conclusion that proteins are formed on hyaloplasmic polysomes for their own needs (for "home" use) of this cell, while on the polysomes of the granular network proteins are synthesized that are removed from the cell and used for the needs of the body (for example, digestive enzymes, breast milk proteins).

Golgi lamellar complex formed by a collection of dictyosomes ranging from several tens (usually about 20) to several hundreds and even thousands per cell.

Dictyosome(Fig. 2.6, A) is represented by a stack of 3-12 flattened disk-shaped cisterns, from the edges of which vesicles (vesicles) are laced off. Limited to a certain area (local) expansion of tanks give larger bubbles (vacuoles). In differentiated cells of vertebrates and humans, dictyosomes are usually assembled in the perinuclear zone of the cytoplasm. In the lamellar complex, secretory vesicles or vacuoles are formed, the contents of which are proteins and other compounds to be removed from the cell. At the same time, the precursor of the secret (prosecret), which enters the dictyosome from the synthesis zone, undergoes some chemical transformations in it. It also separates (segregates) in the form of "portions", which are here dressed in a membrane sheath. Lysosomes are formed in the lamellar complex. In dictyosomes, polysaccharides are synthesized, as well as their complexes with proteins (glycoproteins) and fats (glycolipids), which can then be found in the glycocalyx of the cell membrane.

The shell of mitochondria consists of two membranes that differ in chemical composition, a set of enzymes, and functions. The inner membrane forms invaginations of leaf-shaped (cristae) or tubular (tubules) shape. The space bounded by the inner membrane is matrix organelles. Using an electron microscope, grains with a diameter of 20-40 nm are detected in it. They accumulate calcium and magnesium ions, as well as polysaccharides, such as glycogen.

The matrix contains its own organelle protein biosynthesis apparatus. It is represented by 2 copies of a circular and histone-free (as in prokaryotes) DNA molecule, ribosomes, a set of transport RNA (tRNA), enzymes for DNA replication, transcription and translation of hereditary information. In terms of its main properties: the size and structure of ribosomes, the organization of its own hereditary material, this apparatus is similar to that of prokaryotes and differs from the apparatus of protein biosynthesis in the cytoplasm of a eukaryotic cell (which confirms the symbiotic hypothesis of the origin of mitochondria; see § 1.5). Own DNA genes encode nucleotide sequences mitochondrial rRNA and tRNA, as well as the amino acid sequences of some proteins of the organelle, mainly its inner membrane. The amino acid sequences (primary structure) of most mitochondrial proteins are encoded in the DNA of the cell nucleus and are formed outside the organelle in the cytoplasm.

The main function of mitochondria is to enzymatically extract energy from certain chemicals (by oxidizing them) and to store energy in a biologically usable form (by synthesizing adenosine triphosphate-ATP molecules). In general, this process is called oxidative(disbandment. The components of the matrix and the inner membrane are actively involved in the energy function of mitochondria. It is with this membrane that the electron transport chain (oxidation) and ATP synthetase are connected, catalyzing the oxidation-related phosphorylation of ADP to ATP. Among the side functions of mitochondria, one can name participation in the synthesis of steroid hormones and some amino acids (glutamine).

Lysosomes(Fig. 2.6, IN) are bubbles with a diameter of usually 0.2-0.4 μm, which contain a set of acid hydrolase enzymes that catalyze the hydrolytic (in an aqueous medium) cleavage of nucleic acids, proteins, fats, polysaccharides at low pH values. Their shell is formed by a single membrane, sometimes covered on the outside with a fibrous protein layer (on the electron diffraction patterns "bordered" vesicles). The function of lysosomes is the intracellular digestion of various chemical compounds and structures.

Primary lysosomes(diameter 100nm) are called inactive organelles, secondary - organelles in which digestion takes place. Secondary lysosomes are formed from primary ones. They are subdivided into heterolysosomes(phagolysosomes) and autolysosomes(cytolysosomes). In the first (Fig. 2.6, G) the material entering the cell from the outside is digested by pinocytosis and phagocytosis, secondly, the cell's own structures that have completed their function are destroyed. Secondary lysosomes, in which the digestion process is completed, are called residual bodies(telolisosomes). They lack hydrolases and contain undigested material.

Microbodies make up a group of organelles. These are vesicles with a diameter of 0.1-1.5 μm limited by one membrane with a fine-grained matrix and often crystalloid or amorphous protein inclusions. This group includes, in particular, peroxisomes. They contain oxidase enzymes that catalyze the formation of hydrogen peroxide, which, being toxic, is then destroyed by the action of the peroxidase enzyme. These reactions are included in various metabolic cycles, for example, in the exchange of uric acid in the cells of the liver and kidneys. In the liver cell, the number of peroxisomes reaches 70-100.

Organelles of general importance also include some permanent structures of the cytoplasm, devoid of membranes. microtubules(fig.2.6, D) - tubular formations of various lengths with an outer diameter of 24 nm, a lumen width of 15 nm, and a wall thickness of about 5 nm. They are found in the free state in the cytoplasm of cells or as structural elements of flagella, cilia, mitotic spindle, centrioles. Free microtubules and microtubules of cilia, flagella and centrioles have different resistance to damaging effects, such as chemical (colchicine). Microtubules are built from stereotypical protein subunits by polymerization. In a living cell, polymerization processes proceed simultaneously with depolymerization processes. The ratio of these processes determines the number of microtubules. In the free state, microtubules perform a supporting function, determining the shape of cells, and are also factors in the directed movement of intracellular components.

Microfilaments(Fig. 2.6, E) are called long, thin formations, sometimes forming bundles and found throughout the cytoplasm. There are several different types of microfilaments. actin microfilaments due to the presence of contractile proteins (actin) in them, they are considered as structures that provide cellular forms of movement, for example, amoeboids. They are also credited with a frame role and participation in the organization of intracellular movements of organelles and sections of hyaloplasm.

On the periphery of cells under the plasmalemma, as well as in the perinuclear zone, bundles of microfilaments 10 nm thick are found - intermediate filters. In epithelial, nerve, glial, muscle cells, fibroblasts, they are built from different proteins. Intermediate filaments apparently perform a mechanical, frame function.

Actin microfibrils and intermediate filaments, like microtubules, are built from subunits. Because of this, their number depends on the ratio of polymerization and depolymerization processes.

For animal cells, parts of plant cells, fungi and algae, cell center, which contains centrioles. Centriole(under the electron microscope) looks like a "hollow" cylinder with a diameter of about 150 nm and a length of 300-500 nm. Its wall is formed by 27 microtubules grouped into 9 triplets. The function of centrioles is the formation of mitotic spindle filaments, which are also formed by microtubules. Centrioles polarize the process of cell division, ensuring the separation of sister chromatids (chromosomes) in the anaphase of mitosis.

The eukaryotic cell has a cellular skeleton (cytoskeleton) of intracellular fibers (Koltsov) - the beginning of the 20th century, it was rediscovered at the end of 1970. This structure allows the cell to have its shape, sometimes changing it. The cytoplasm is in motion. The cytoskeleton is involved in the process of transfer of organelles, is involved in cell regeneration.

Mitochondria are complex formations with a double membrane (0.2-0.7 microns) and different shapes. The inner membrane has cristae. The outer membrane is permeable to almost all chemicals, while the inner membrane is permeable only to active transport. Between the membranes is the matrix. Mitochondria are located where energy is needed. Mitochondria have a system of ribosomes, a DNA molecule. Mutations may occur (more than 66 diseases). As a rule, they are associated with insufficient ATP energy, often associated with cardiovascular insufficiency, pathologies. The number of mitochondria is different (in a trypanosome cell - 1 mitochondria). The amount depends on age, function, tissue activity (liver - more than 1000).

Lysosomes are bodies surrounded by an elementary membrane. Contain 60 enzymes (40 lysosomal, hydrolytic). Inside the lysosome is a neutral environment. They are activated by low pH values, leaving the cytoplasm (self-digestion). Lysosome membranes protect the cytoplasm and cells from destruction. They are formed in the Golgi complex (intracellular stomach, they can process cells that have worked out their structures). There are 4 kinds. 1-primary, 2-4 - secondary. Substance enters the cell by endocytosis. The primary lysosome (storage granule) with a set of enzymes absorbs the substance and a digestive vacuole is formed (with complete digestion, splitting goes to low molecular weight compounds). Undigested residues remain in residual bodies, which can accumulate (lysosomal storage diseases). Residual bodies that accumulate in the embryonic period lead to gargaleism, deformities, and mucopolysaccharidoses. Autophagic lysosomes destroy the cell's own structures (unnecessary structures). May contain mitochondria, parts of the Golgi complex. Often formed during starvation. May occur when exposed to other cells (erythrocytes).