Eps is part of the Golgi complex. Single membrane structures

The Golgi apparatus is a single-membrane, microscopic organelle of a eukaryotic cell, which is designed to complete cell synthesis processes and ensure the removal of formed substances.

Study structural components The development of the Golgi complex began back in 1898 by the Italian histologist Camillo Golgi, and the organelle was named after him. The study of the organoid took place for the first time as part of a nerve cell.

Structure of the Golgi complex

The lamellar complex (Golgi apparatus) has three parts:

• Cis tank- located near the nucleus, constantly interacting with the granular endoplasmic reticulum;
• media tank or intermediate part;
• trans tank- distant from the nucleus, gives tubular branches, forming the trans-Golgi network.

The lamellar complex in cells of different nature and even at different stages of differentiation of one cell sometimes has distinctive features in the building.

Characteristic features of the Golgi apparatus

It has the appearance of a stack, which consists of three to eight tanks, about 25 nm thick, they are flattened in the central part and expand towards the periphery, resembling a stack of inverted plates. The surfaces of the tanks are adjacent to each other very tightly. Small membrane vesicles bud from the peripheral part.

Human cells have one, or less often a pair of stacks, and plant cells can contain several such formations. The collection of cisternae (one stack) together with the vesicles surrounding it is called a dictyosome. Several dictyosomes can communicate with each other, forming a network.

Polarity– the presence of a cis side directed towards the EPS and the nucleus, where the fusion of vesicles occurs, and a trans side directed towards the cell membrane (this feature is clearly visible in the cells of secreting organs).

Asymmetry– the side located closer to the cell nucleus (proximal pole) contains “immature” proteins, vesicles detached from the EPS are constantly attached to it, the trans side (distal, mature pole) contains already modified proteins.

When the lamellar complex is destroyed by foreign agents, the Golgi apparatus is divided into separate parts, but its main functions are preserved. After the resumption of the microtubule system, which was chaotically scattered in the cytoplasm, parts of the apparatus are assembled and again turn into a normally functioning lamellar complex. Physiological separation also occurs under normal conditions of cell activity, during indirect division.

ER and Golgi complex

Is the ER part of the Golgi complex?

Definitely not. The endoplasmic reticulum is an independent membrane organelle, which is built from a system of closed tubules and cisterns formed by a continuous membrane. The main function is the synthesis of proteins using ribosomes located on the surface of the granular EPS.

There are a number of similar features between the ER and the Golgi apparatus:

• These are intracellular formations delimited from the cytoplasm by a membrane;
• separate membrane vesicles that are filled with organic synthesis products;
• together they form a single synthesizing system;
• in secreting cells have largest dimensions And high level development.

What are the walls of the endoplasmic reticulum and Golgi complex formed by?

The walls of the ER and Golgi apparatus are presented in the form of a single-layer membrane. These organelles, together with lysosomes, peroxisomes and mitochondria, are combined into a group of membrane organelles.

What happens in the Golgi complex with hormones and enzymes?

The endoplasmic reticulum is responsible for the synthesis of hormones; the production of hormonal substances occurs on the surface of its membrane. Synthesized hormones enter the Golgi complex, where they accumulate, then they are processed and excreted. Therefore, in the cells of endocrine organs there are complexes large sizes(up to 10 microns).

Functions of the Golgi complex

Proteolysis protein substances, which leads to the activation of proteins, so proinsulin turns into insulin.

Provides transport of EPS synthesis products from the cell.

The most important function of the Golgi complex is considered to be the removal of synthesis products from the cell, which is why it is also called the cell transport apparatus.

Synthesis of polysaccharides, such as pectin, hemicellulose, which are part of the membranes of plant cells, the formation of glycosaminoglycans, one of the components of the intercellular fluid.

In the tanks of the plate complex there is maturation of proteins, necessary for secretion, transmembrane proteins of the cell membrane, lysosome enzymes, etc. During the process of maturation, proteins gradually move through the sections of the organelle, in which their formation is completed and glycosylation and phosphorylation occur.

Formation of lipoprotein substances. Synthesis and accumulation of mucous substances (mucin). Formation of glycolipids, which are part of the membrane glycocalyx.

Transfers proteins in three directions: to lysosomes (transfer is controlled by the enzyme mannose-6-phosphate), to membranes or the intracellular environment, and to the intercellular space.

Together with grained EPS forms lysosomes, by fusion of budding vesicles with autolytic enzymes.

Exocytotic transport– the vesicle, approaching the membrane, is embedded into it and leaves its contents on the outside of the cell.

Summary table of functions of the Golgi complex

Structural unit	Functions
Cis tank	Capture of synthesized EPS proteins and membrane lipids
Middle tanks	Post-translational modifications associated with the transfer of acetylglucosamine.
Trans tank	Glycosylation is completed, galactose and sialic acid are added, and substances are sorted for further transport out of the cell.
Bubbles	They are responsible for the transfer of lipids and proteins to the Golgi apparatus and between cisternae, as well as for the excretion of synthesis products.

The endoplasmic reticulum, or endoplasmic reticulum, is a system of tubes and cavities that penetrate the cytoplasm of the cell. The ER is formed by a membrane that has the same structure as the plasma membrane. ER tubes and cavities can occupy up to 50% of the cell volume and do not break off anywhere or open into the cytoplasm. There are smooth and rough (granular) EPS. The rough ER contains many ribosomes. This is where most proteins are synthesized. On the surface of the smooth EPS, carbohydrates and lipids are synthesized.

Functions of the granular endoplasmic reticulum:

• · synthesis of proteins intended for removal from the cell (“for export”);
• · separation (segregation) of the synthesized product from the hyaloplasm;
• · condensation and modification of synthesized protein;
• · transport of synthesized products into the tanks of the lamellar complex or directly from the cell;
• · synthesis of bilipid membranes.

The smooth endoplasmic reticulum is represented by cisterns, wider channels and individual vesicles, on the outer surface of which there are no ribosomes.

Functions of smooth endoplasmic reticulum:

• · participation in glycogen synthesis;
• lipid synthesis;
• · detoxification function - neutralization of toxic substances by combining them with other substances.

Golgi complex (apparatus).

The system of intracellular cisterns in which substances synthesized by the cell accumulate is called the Golgi complex (apparatus). Here these substances undergo further biochemical transformations, are packaged into membrane vesicles and transported to those places in the cytoplasm where they are needed, or are transported to cell membrane and extend beyond the cell (Fig. 32). The Golgi complex is built from membranes and is located next to the ER, but does not communicate with its channels. Therefore, all substances synthesized on the EPS membranes are transferred to the Golgi complex inside membrane vesicles that bud from the EPS and then merge with the Golgi complex. Another important function of the Golgi complex is the assembly of cell membranes. The substances that make up membranes (proteins, lipids) enter the Golgi complex from the ER; membrane sections from which special membrane vesicles are made are collected in the cavities of the Golgi complex. They move through the cytoplasm to those places in the cell where the membrane needs to be completed.

Functions of the Golgi apparatus:

• · sorting, accumulation and removal of secretory products;
• · accumulation of lipid molecules and formation of lipoproteins;
• · formation of lysosomes;
• · synthesis of polysaccharides for the formation of glycoproteins, waxes, gums, mucus, substances of the matrix of plant cell walls;
• · formation of a cell plate after nuclear division in plant cells;
• · formation of contractile vacuoles of protozoa.

Golgi complex It is a stack of membrane sacs (cisterns) and an associated system of bubbles.

On the outer, concave side there is a stack of bubbles budding from the smooth. EPS, new tanks are constantly forming, and on the inside of the tank they turn back into bubbles.

The main function of the Golgi complex is the transport of substances into the cytoplasm and extracellular environment, as well as the synthesis of fats and carbohydrates. The Golgi complex is involved in growth and renewal plasma membrane and in the formation of lysosomes.

The Golgi complex was discovered in 1898 by C. Golgi. Having extremely primitive equipment and a limited set of reagents, he made a discovery, thanks to which, together with Ramon y Cajal, he received Nobel Prize. He processed nerve cells dichromate solution, after which silver and osmium nitrates were added. By precipitating osmium or silver salts with cellular structures, Golgi discovered a dark-colored network in neurons, which he called the internal reticular apparatus. When stained using general methods, the lamellar complex does not accumulate dyes, so the zone of its concentration is visible as a light area. For example, near the nucleus of a plasma cell, a light zone is visible, corresponding to the area where the organelle is located.

Most often, the Golgi complex is adjacent to the nucleus. With light microscopy, it can be distributed in the form of complex networks or individual diffusely located areas (dictyosomes). The shape and position of the organelle are not of fundamental importance and can vary depending on the functional state of the cell.

The Golgi complex is the site of condensation and accumulation of secretion products produced in other parts of the cell, mainly in the ER. During protein synthesis, radiolabeled amino acids accumulate in gr. ER, and then they are found in the Golgi complex, secretory inclusions or lysosomes. This phenomenon makes it possible to determine the significance of the Golgi complex in synthetic processes in the cell.

Electron microscopy shows that the Golgi complex consists of clusters of flat cisterns called dictyosomes. The tanks are closely adjacent to each other at a distance of 20...25 nm. The lumen of the cisterns in the central part is about 25 nm, and at the periphery expansions are formed - ampoules, the width of which is not constant. Each stack contains about 5...10 tanks. In addition to densely located flat cisterns, in the zone of the Golgi complex there is large number small bubbles (vesicles), especially at the edges of the organelle. Sometimes they become detached from the ampoules.

On the side adjacent to the ER and the nucleus, the Golgi complex has a zone containing a significant number of small vesicles and small cisterns.

The Golgi complex is polarized, that is, it is qualitatively heterogeneous with different sides. It has an immature cis surface, lying closer to the nucleus, and a mature trans surface, facing the cell surface. Accordingly, the organelle consists of several interconnected compartments that perform specific functions.

The cis compartment usually faces cell center. Its outer surface has a convex shape. Microvesicles (transport pinocytosis vesicles) coming from the EPS merge with the cisterns. Membranes are constantly renewed due to vesicles and, in turn, replenish the contents of membrane formations in other compartments. Post-translational processing of proteins begins in the compartment and continues next parts complex.

The intermediate compartment carries out glycosylation, phosphorylation, carboxylation, and sulfation of biopolymer protein complexes. The so-called post-translational modification of polypeptide chains occurs. Synthesis of glycolipids and lipoproteins is underway. In the intermediate compartment, as in the cis-compartment, tertiary and quaternary protein complexes are formed. Some proteins undergo partial proteolysis (destruction), which is accompanied by their transformation necessary for maturation. Thus, the cis and intermediate compartments are required for the maturation of proteins and other complex biopolymer compounds.

The trans compartment is located closer to the cell periphery. Its outer surface is usually concave. The trans-compartment partially transforms into the trans-network - a system of vesicles, vacuoles and tubules.

In cells, individual dictyosomes can be linked to each other by a system of vesicles and cisternae adjacent to the distal end of a cluster of flat sacs, so that a loose three-dimensional network is formed - a trans-network.

In the structures of the trans compartment and trans network, the sorting of proteins and other substances, the formation of secretory granules, precursors of primary lysosomes and spontaneous secretion vesicles occur. Secretory vesicles and prelysosomes are surrounded by proteins called clathrins.

Clathrins are deposited on the membrane of the forming vesicle, gradually splitting it off from the distal cistern of the complex. Bordered vesicles extend from the trans-network; their movement is hormone-dependent and controlled by the functional state of the cell. The transport process of bordered vesicles is influenced by microtubules. Protein (clathrin) complexes around the vesicles disintegrate after the vesicle is detached from the trans-network and form again at the moment of secretion. At the moment of secretion, protein complexes of the vesicles interact with microtubule proteins, and the vesicle is transported to the outer membrane. Spontaneous secretion vesicles are not surrounded by clathrins; their formation occurs continuously and, heading towards the cell membrane, they merge with it, ensuring the restoration of the cytolemma.

In general, the Golgi complex is involved in segregation - this is separation, separation certain parts from the bulk, and the accumulation of products synthesized in EPS, in their chemical rearrangements and maturation. In the tanks, polysaccharides are synthesized and combined with proteins, which leads to the formation of complex complexes of peptidoglycans (glycoproteins). With the help of elements of the Golgi complex, ready-made secretions are removed outside the secretory cell.

Small transport bubbles split off from the gr. EPS in ribosome-free zones. The vesicles restore the membranes of the Golgi complex and deliver polymer complexes synthesized in the ER. The vesicles are transported to the cis compartment, where they fuse with its membranes. Consequently, new portions of membranes and products synthesized in the group enter the Golgi complex. EPS.

In the cisternae of the Golgi complex, secondary changes occur in proteins synthesized in the group. EPS. These changes are associated with the rearrangement of oligosaccharide chains of glycoproteins. Inside the cavities of the Golgi complex, lysosomal proteins and secretion proteins are modified with the help of transglucosidases: oligosaccharide chains are successively replaced and extended. Modifying proteins move from the cis-compartment cisternae to the trans-compartment cisternae due to transport in vesicles containing the protein.

In the trans-compartment, proteins are sorted: on the inner surfaces of the cisternae membranes there are protein receptors that recognize secretory proteins, membrane proteins and lysosomes (hydrolases). As a result, three types of small vacuoles are split off from the distal trans-sections of dictyosomes: prelysosomes containing hydrolases; with secretory inclusions, vacuoles that replenish the cell membrane.

The secretory function of the Golgi complex is that the exported protein synthesized on ribosomes, separated and accumulated inside the ER cisterns, is transported to the vacuoles of the lamellar apparatus. The accumulated protein may then condense to form secretory protein granules (in the pancreas, mammary glands, and other glands) or remain dissolved (immunoglobulins in plasma cells). Vesicles containing these proteins are split off from the ampullary extensions of the cisterns of the Golgi complex. Such vesicles can merge with each other and increase in size, forming secretory granules.

After this, the secretory granules begin to move to the cell surface, come into contact with the plasmalemma, with which their own membranes merge, and the contents of the granules appear outside the cell. Morphologically, this process is called extrusion, or excretion (throwing out, exocytosis) and resembles endocytosis, only with the reverse sequence of stages.

The Golgi complex can sharply increase in size in cells actively performing secretory function, which is usually accompanied by the development of the ER, and in the case of protein synthesis, the nucleolus.

During cell division, the Golgi complex breaks down into individual cisterns (dictyosomes) and/or vesicles, which are distributed between the two dividing cells and, at the end of telophase, restore the structural integrity of the organelle. Outside of division, the membrane apparatus is continuously renewed due to vesicles migrating from the EPS and distal cisternae of the dictyosome at the expense of the proximal compartments.

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A lysosome is a single-membrane organelle of a eukaryotic cell, mainly spherical in shape and not exceeding 1 μm in size. Characteristic of animal cells, where they can be contained in large quantities(especially in cells capable of phagocytosis). In plant cells, many of the functions of lysosomes are performed by the central vacuole.

Structure of a lysosome

Lysosomes are separated from the cytoplasm by several dozen hydrolytic (digestive) enzymes, breaking down proteins, fats, carbohydrates and nucleic acids. Enzymes belong to the groups of proteases, lipases, nucleases, phosphatases, etc.

Unlike hyaloplasm, internal environment lysosomes are acidic, and the enzymes contained here are active only at low pH.

Isolation of lysosome enzymes is necessary, otherwise, once in the cytoplasm, they can destroy cellular structures.

Lysosome formation

Lysosomes are formed in. Enzymes (essentially proteins) of lysosomes are synthesized on the rough surface, after which they are transported to the Golgi using vesicles (membrane-bounded vesicles). Here proteins are modified, acquire their functional structure, and are packaged into other vesicles - lysosomes are primary, – which detach from the Golgi apparatus. Further, turning into secondary lysosomes, perform the function of intracellular digestion. In some cells, primary lysosomes secrete their enzymes beyond the cytoplasmic membrane.

Functions of lysosomes

The functions of lysosomes are already indicated by their name: lysis - splitting, soma - body.

When nutrients or any microorganisms enter the cell, lysosomes take part in their digestion. In addition, they destroy unnecessary structures of the cell itself and even entire organs of organisms (for example, the tail and gills during the development of many amphibians).

Below is a description of the main, but not the only functions of lysosomes.

Digestion of particles entering the cell by endocytosis

By endocytosis (phogocytosis and pinocytosis) relatively large materials enter the cell ( nutrients, bacteria, etc.). In this case, the cytoplasmic membrane is invaginated into the cell, a structure or substance gets into the invagination, after which the invagination is laced inward, and a vesicle is formed ( endosome), surrounded by a membrane, – phagocytic (with solid particles) or pinocytic (with solutions).

Food absorption can occur in a similar way (for example, in amoebas). In this case, the secondary lysosome is also called digestive vacuole. Digested substances enter the cytoplasm from the secondary lysosome. Another option is the digestion of bacteria that have entered the cell (observed in phagocytes - leukocytes specialized for protecting the body).

The unnecessary substances remaining in the secondary lysosome are removed from the cell by exocytosis (the reverse of endocytosis). A lysosome with undigested substances to be removed is called residual body.

Autophagy

By autophagy (autophagy) the cell gets rid of its own structures (various organelles, etc.) that it does not need.

First, such an organelle is surrounded by an elementary membrane separated from the smooth ER. After this, the resulting vesicle merges with the primary lysosome. A secondary lysosome is formed, which is called autophagy vacuole. Digestion of cellular structure occurs in it.

Autophagy is especially pronounced in cells in the process of differentiation.

Autolysis

Under autolysis understand cell self-destruction. Characteristic during metamorphosis and tissue necrosis.

Autolysis occurs when the contents of many lysosomes are released into the cytoplasm. Usually, in a fairly neutral environment of the hyaloplasm, lysosome enzymes that require an acidic environment become inactive. However, when many lysosomes are destroyed, the acidity of the environment increases, but the enzymes remain active and break down cellular structures.

Membrane organelles. Each membrane organelle represents a cytoplasmic structure bounded by a membrane. As a result, a space is formed inside it, delimited from the hyaloplasm. The cytoplasm is thus divided into separate compartments with their own properties - compartments (English compartment - department, compartment, compartment). The presence of compartments is one of important features eukaryotic cells.

Membranous organelles include mitochondria, endoplasmic reticulum (ER), Golgi complex, lysosomes and peroxisomes.

Mitochondria - « energy stations cells,” participate in the processes of cellular respiration and convert the energy that is released into a form available for use by other cell structures.

Mitochondria, unlike other organelles, have their own genetic system necessary for their self-reproduction and protein synthesis. They have their own DNA, RNA and ribosomes, which differ from those in the nucleus and other parts of the cytoplasm of their own cell. At the same time, mitochondrial DNA, RNA and ribosomes are very similar to prokaryotic ones. This was the impetus for the development of the symbiotic hypothesis, according to which mitochondria (and chloroplasts) arose from symbiotic bacteria. Mitochondrial DNA ring-shaped (like bacteria), it accounts for about 2% of the cell's DNA.

Mitochondria (and chloroplasts ) are able to reproduce in a cell by binary fission. Thus, they are self-replicating organelles. At the same time genetic information, contained in their DNA, does not provide them with all the proteins necessary for complete self-reproduction; Some of these proteins are encoded by nuclear genes and enter the mitochondria from the hyaloplasm. Therefore, mitochondria are called semi-autonomous structures in relation to their self-reproduction. In humans and other mammals, the mitochondrial genome is inherited from the mother: when the egg is fertilized, sperm mitochondria do not penetrate into it.

Each mitochondrion is formed by two membranes - outer and inner (13). Between them there is an intermembrane space with a width of 10 - 20 nm. The outer membrane is smooth, while the inner one forms numerous cristae, which can take the form of folds, tubes and ridges. Thanks to the cristae, the area of ​​the inner membrane increases significantly.

The space limited by the inner membrane is filled with colloidal mitochondrial matrix. It has a fine-grained structure and contains many different enzymes. The matrix also contains the mitochondria's own genetic apparatus (in plants, in addition to mitochondria, DNA is also contained in chloroplasts).

On the matrix side, many electron-dense submitochondrial cells are attached to the surface of the cristae. elementary particles(up to 4000 per 1 µm2 membrane). Each of them is shaped like a mushroom (see 13). These particles contain ATPases - enzymes that directly ensure the synthesis and breakdown of ATP. These processes are inextricably linked with the tricarboxylic acid cycle (Krebs cycle).

The number, size and location of mitochondria depend on the function of the cell, in particular its energy needs and where the energy is spent. Thus, in one liver cell their number reaches 2500. Many large mitochondria are contained in cardiomyocytes and myosymplasts of muscle fibers. In sperm cells, cristae-rich mitochondria surround the axoneme of the intermediate part of the flagellum.

Endoplasmic reticulum (ER) or endoplasmic reticulum (ER) ), is a single continuous compartment bounded by a membrane that forms many invaginations and folds (14). Therefore, in electron microscopic photographs, the endoplasmic reticulum appears in the form of many tubes, flat or round cisterns, and membrane vesicles. On the membranes of the ER, various primary syntheses of substances necessary for the life of the cell take place. The molecules of these substances will undergo further chemical transformations in other compartments of the cell.

Most substances are synthesized on the outer surface of EPS membranes. These substances are then transported through the membrane into the compartment and there transported to sites of further biochemical transformations, in particular to the Golgi complex. At the ends of the EPS tubes they accumulate and then separate

from them in the form of transport bubbles. Each vesicle is thus surrounded by a membrane and moves through the hyaloplasm to its destination. As always, microtubules take part in transport.

There are two types of EPS: granular (granular, rough) and agranular (smooth). Both of them represent a single structure.

The outer side of the granular ER membrane, facing the hyaloplasm, is covered with ribosomes. Protein synthesis takes place here. In cells specialized in protein synthesis, the granular endoplasmic reticulum appears in the form of parallel fenestrated (fenestrated) lamellar structures communicating with each other and with the perinuclear space, between which there are many free ribosomes.

The surface of the smooth ER is devoid of ribosomes. The network itself consists of many small tubes with a diameter of about 50 nm each.

Carbohydrates and lipids are synthesized on the membranes of the smooth network, among them glycogen and cholesterol. As a depot of calcium ions, the smooth endoplasmic reticulum is involved in the contraction of cardiomyocytes and skeletal fibers. muscle tissue. It also distinguishes future platelets in megakaryocytes. Its role is extremely important in the detoxification by hepatocytes of substances that come from the intestinal cavity through the portal vein into the hepatic capillaries.

Through the lumens of the endoplasmic reticulum, synthesized substances are transported to Golgi complex (but the lumens of the network do not communicate with the lumens of the tanks of the latter). Substances enter the Golgi complex in vesicles, which are first detached from the network, transported to the complex, and finally merge with it. From the Golgi complex, substances are transported to their places of use also in membrane vesicles. It should be emphasized that one of the essential functions The endoplasmic reticulum is the synthesis of proteins and lipids for all cellular organelles.

Most often, three membrane elements are detected in CG: flattened sacs (cisterns), vesicles and vacuoles (15). The main elements of the Golgi complex are dictyosomes (Greek dyction - network). Their number fluctuates different cells from one to several hundred. The ends of the tanks are widened. Bubbles and vacuoles, surrounded by a membrane and containing various substances, break off from them.

The widest flattened tanks face the EPS. They are joined by transport bubbles carrying substances - products of primary syntheses. In the tanks, the macromolecules brought in are modified. Here, the synthesis of polysaccharides, modification of oligosaccharides, formation of protein-carbohydrate complexes and covalent modification of transported macromolecules occurs.

As modifications occur, substances move from one tank to another. Outgrowths appear on the side surfaces of the tanks, where substances move. The outgrowths split off in the form of vesicles, which move away from the CG in various directions along the hyaloplasm.

The side of the CG where substances from the EPS arrive is called the cis-pole (forming surface), the opposite side is called the trans-pole (mature surface). Thus, the Golgi complex is structurally and biochemically polarized.

The fate of the bubbles splitting off from the CG is different. Some of them are directed to the cell surface and remove synthesized substances into the intercellular matrix. Some of these substances are metabolic products, while others are specially synthesized products that have biological activity (secrets). The process of packaging substances into bubbles consumes a significant amount of membrane material. Membrane assembly is another of the functions of the CG. This assembly is made from substances coming, as usual, from the EPS.

In all cases, mitochondria are concentrated near the Golgi complex. This is due to the energy-dependent reactions occurring in it.

Lysosomes . Each lysosome is a membrane vesicle with a diameter of 0.4 - 0.5 microns. It contains about 50 types of various hydrolytic enzymes in a deactivated state (proteases, lipases, phospholipases, nucleases, glycosidases, phosphatases, including acid phosphatase; the latter is a marker of lysosomes). The molecules of these enzymes, as always, are synthesized on the ribosomes of granular EPS, from where they are transported by transport vesicles to the CG, where they are modified. Primary lysosomes bud from the mature surface of the CG cisterns.

All lysosomes of the cell form a lysosomal space, in which an acidic environment is constantly maintained with the help of a proton pump - the pH ranges from 3.5-5.0. The membranes of lysosomes are resistant to the enzymes contained in them and protect the cytoplasm from their action.

Function of lysosomes- intracellular lysis (“digestion”) of high-molecular compounds and particles. The trapped particles are usually surrounded by a membrane. Such a complex is called a phagosome.

The process of intracellular lysis occurs in several stages. First, the primary lysosome fuses with the phagosome. Their complex is called the secondary lysosome (phagolysosome). In the secondary lysosome, enzymes are activated and break down polymers entering the cell into monomers. The breakdown products are transported across the lysosomal membrane into the cytosol. Undigested substances remain in the lysosome and can remain in the cell for a very long time in the form of residual bodies surrounded by a membrane.

Residual bodies are classified not as organelles, but as inclusions. Another transformation path is also possible: the substances in the phagosome are completely broken down, after which the phagosome membrane disintegrates. Secondary lysosomes can fuse with each other, as well as with other primary lysosomes. In this case, sometimes peculiar secondary lysosomes are formed - multivesicular bodies.

During the life of a cell, restructuring of structures constantly occurs at different hierarchical levels of its organization, starting from molecules and ending with organelles. Near areas of the cytoplasm that are damaged or require replacement, usually in the vicinity of the Golgi complex, a semilunar double membrane is formed, which grows, surrounding the damaged areas on all sides. This structure then fuses with lysosomes. In such an autophagosome (autosome), lysis of organelle structures occurs.

In other cases, during the process of macro- or microautophagy, structures to be digested (for example, secretion granules) are invaginated into the lysosomal membrane, surrounded by it and subjected to digestion. An autophagic vacuole is formed. As a result of multiple microautophagy, multivesicular bodies are also formed (for example, in brain neurons and cardiomyocytes). Along with autophagy, crinophagy also occurs in some cells (Greek krinein - sift, separate) - fusion