In 1898, the Italian scientist C. Golgi discovered mesh formations in nerve cells, which he called the “internal mesh apparatus” (Fig. 174). Reticulate structures (Golgi apparatus) are found in all cells of any eukaryotic organisms. Typically, the Golgi apparatus is located near the nucleus, near the cell center (centriole).

Fine structure of the Golgi apparatus. The Golgi apparatus consists of membrane structures assembled together in a small zone (Fig. 176, 177). A separate zone of accumulation of these membranes is called dictyosome(Fig. 178). In the dictyosome, flat membrane sacs, or cisterns, are located close to each other (at a distance of 20-25 nm) in the form of a stack, between which thin layers of hyaloplasm are located. Each individual tank has a diameter of about 1 μm and variable thickness; in the center its membranes can be close together (25 nm), and at the periphery they can have expansions, ampoules, the width of which is not constant. The number of such bags in a stack usually does not exceed 5-10. In some single-celled organisms their number can reach 20. In addition to densely located flat cisterns, many vacuoles are observed in the AG zone. Small vacuoles are found mainly in the peripheral areas of the AG zone; sometimes you can see how they are laced from the ampullary extensions at the edges of the flat cisterns. It is customary to distinguish in the dictyosome zone the proximal or developing, cis-section, and the distal or mature, trans-section (Fig. 178). Between them is the middle or intermediate section of the AG.

During cell division, the reticulate forms of AG disintegrate into dictyosomes, which are passively and randomly distributed among daughter cells. As cells grow, the total number of dictyosomes increases.

In secreting cells, the AG is usually polarized: its proximal part faces the cytoplasm and nucleus, and the distal part faces the cell surface. In the proximal area, the stacks of closely spaced cisterns are adjacent to a network-like or sponge-like system of membrane cavities. It is believed that this system represents the zone of transition of ER elements into the zone of the Golgi apparatus (Fig. 179).

In the middle part of the dictyosome, the periphery of each cistern is also accompanied by a mass of small vacuoles about 50 nm in diameter.

In the distal or trans-section of dictyosomes, the last membrane flat cistern is adjacent to a section consisting of tubular elements and a mass of small vacuoles, often having fibrillar pubescence along the surface on the cytoplasmic side - these are pubescent or bordered vesicles of the same type as the bordered vesicles during pinocytosis. This is the so-called trans-Golgi network (TGN), where the separation and sorting of secreted products occurs. Even more distal is a group of larger vacuoles - this is the product of the fusion of small vacuoles and the formation of secretory vacuoles.

Using a megavoltage electron microscope, it was established that in cells individual dictyosomes can be connected to each other by a system of vacuoles and cisterns and form a loose three-dimensional network that can be detected in a light microscope. In the case of the diffuse form of AG, each individual section is represented by a dictyosome. In plant cells, the diffuse type of AG organization predominates; usually, on average, there are about 20 dictyosomes per cell. In animal cells, centrioles are often associated with the membrane zone of the Golgi apparatus; between the bundles of microtubules extending radially from them lie groups of stacks of membranes and vacuoles, which concentrically surround the cell center. This connection indicates the participation of microtubules in the movement of vacuoles.

Secretory function of the Golgi apparatus. The main functions of AG are the accumulation of products synthesized in the ER, ensuring their chemical rearrangements and maturation.

In the AG tanks, the synthesis of polysaccharides and their interaction with proteins occurs. and the formation of mucoproteins. But the main function of the Golgi apparatus is to remove ready-made secretions outside the cell. In addition, AG is a source of cellular lysosomes.

The exported protein synthesized on ribosomes is separated and accumulates inside the ER cisterns, through which it is transported to the AG membrane zone. Here, small vacuoles containing the synthesized protein are split off from the smooth areas of the ER and enter the vacuole zone in the proximal part of the dictyosome. At this point, the vacuoles merge with each other and with the flat cis cisternae of the dictyosome. In this way, the protein product is transferred already inside the cavities of the AG tanks.

As proteins in the cisternae of the Golgi apparatus are modified, small vacuoles are used to transport them from cisternae to cisternae into the distal part of the dictyosome until they reach the tubular membrane network in the trans region of the dictyosome. In this area, small bubbles containing an already mature product are separated. The cytoplasmic surface of such vesicles is similar to the surface of bordered vesicles that are observed during receptor pinocytosis. The separated small vesicles merge with each other and form secretory vacuoles. After this, the secretory vacuoles begin to move towards the cell surface, the plasma membrane and the vacuole membranes fuse, and thus the contents of the vacuoles appear outside the cell. Morphologically, this process of extrusion (throwing out) resembles pinocytosis, only with the reverse sequence of stages. It is called exocytosis.

In the Golgi apparatus, not only the movement of products from one cavity to another occurs, but also the modification of proteins occurs, which ends with the targeting of products either to lysosomes, the plasma membrane or to secretory vacuoles.

Modification of proteins in the Golgi apparatus. Proteins synthesized in the ER enter the cis-zone of the Golgi apparatus after primary glycosylation and reduction of several saccharide residues. After which all proteins receive the same oligosaccharide chains, consisting of two molecules of N-acetylglucosamine and six molecules of mannose (Fig. 182). In cis-cisternae, secondary modification of oligosaccharide chains occurs and their sorting into two classes. The sorting results in one class of phosphorylatable oligosaccharides (mannose-rich) for hydrolytic enzymes destined for lysosomes, and another class of oligosaccharides for proteins destined for secretory granules or the plasma membrane

The transformations of oligosaccharides are carried out with the help of enzymes - glycosyltransferases, which are part of the membranes of the Golgi apparatus cisterns. Since each zone in dictyosomes has its own set of glycosylation enzymes, glycoproteins are transferred, as if in a relay race, from one membrane compartment (“floor” in a stack of dictyosome tanks) to another and in each are subjected to the specific action of enzymes. Thus, in the cis-site, phosphorylation of mannoses in lysosomal enzymes occurs and a special mannose-6 group is formed, characteristic of all hydrolytic enzymes, which then enter the lysosomes.

In the middle part of dictyosomes, secondary glycosylation of secretory proteins occurs: additional removal of mannose and addition of N-acetylglucosamine. In the trans region, galactose and sialic acids are added to the oligosaccharide chain (Fig. 183).

In a number of specialized cells in the Golgi apparatus, the synthesis of polysaccharides themselves occurs.

In the Golgi apparatus of plant cells, polysaccharides of the cell wall matrix (hemicelluloses, pectins) are synthesized. Dictyosomes of plant cells are involved in the synthesis and secretion of mucus and mucins, which also include polysaccharides. The synthesis of the main framework polysaccharide of plant cell walls, cellulose, occurs on the surface of the plasma membrane.

In the Golgi apparatus of animal cells, long unbranched polysaccharide chains of glycosaminoglycans are synthesized. Glucosaminoglycans covalently bind to proteins and form proteoglycans (mucoproteins). Such polysaccharide chains are modified in the Golgi apparatus and bind to proteins, which are secreted by cells in the form of proteoglycans. Sulfation of glycosaminoglycans and some proteins also occurs in the Golgi apparatus.

Sorting of proteins in the Golgi apparatus. Ultimately, three streams of non-cytosolic proteins synthesized by the cell pass through the Golgi apparatus: a stream of hydrolytic enzymes for lysosomes, a stream of secreted proteins that accumulate in secretory vacuoles and are released from the cell only upon receipt of special signals, a stream of constantly secreted secretory proteins. Consequently, in the cell there is a mechanism for the spatial separation of different proteins and their pathways.

In the cis- and middle zones of dictyosomes, all these proteins go together without separation, they are only separately modified depending on their oligosaccharide markers.

The actual separation of proteins, their sorting, occurs in the trans region of the Golgi apparatus. The principle of selection of lysosomal hydrolases occurs as follows (Fig. 184).

Precursor proteins of lysosomal hydrolases have an oligosaccharide, more specifically a mannose group. In cis cisternae, these groups are phosphorylated and, together with other proteins, are transferred to the trans region. The membranes of the trans-network of the Golgi apparatus contain a transmembrane protein receptor (mannose-6-phosphate receptor or M-6-P receptor), which recognizes phosphorylated mannose groups of the oligosaccharide chain of lysosomal enzymes and binds to them. Consequently, M-6-F receptors, being transmembrane proteins, bind to lysosomal hydrolases, separate them, sort them from other proteins (for example, secretory, non-lysosomal) and concentrate them in bordered vesicles. Having become detached from the trans-network, these vesicles quickly lose their borders and merge with endosomes, thus transferring their lysosomal enzymes associated with membrane receptors into this vacuole. Inside endosomes, due to the activity of the proton transporter, acidification of the environment occurs. Starting at pH 6, lysosomal enzymes dissociate from M-6-P receptors, are activated and begin to work in the cavity of the endolysosome. Sections of membranes, together with M-6-F receptors, are returned by recycling membrane vesicles back into the trans-network of the Golgi apparatus.

It is possible that part of the proteins that accumulate in secretory vacuoles and are removed from the cell after receiving a signal (for example, nervous or hormonal) undergoes the same selection and sorting procedure on the receptors of the trans-cisterns of the Golgi apparatus. Secretory proteins also first enter small clathrin-clad vacuoles and then fuse with each other. In secretory vacuoles, proteins accumulate in the form of dense secretory granules, which leads to an increase in protein concentration in these vacuoles by approximately 200 times compared to its concentration in the Golgi apparatus. As proteins accumulate in secretory vacuoles and after the cell receives the appropriate signal, they are released from the cell by exocytosis.

The third stream of vacuoles, associated with constant, constitutive secretion, also emanates from the Golgi apparatus. For example, fibroblasts secrete a large amount of glycoproteins and mucins that are part of the ground substance of connective tissue. Many cells constantly secrete proteins that facilitate their binding to substrates; there is a constant flow of membrane vesicles to the cell surface, carrying elements of the glycocalyx and membrane glycoproteins. This flow of components secreted by the cell is not subject to sorting in the receptor trans-system of the Golgi apparatus. The primary vacuoles of this flow also split off from the membranes and are related in their structure to bordered vacuoles containing clathrin (Fig. 185).

Concluding the consideration of the structure and operation of such a complex membrane organelle as the Golgi apparatus, it is necessary to emphasize that despite the apparent morphological homogeneity of its components, the vacuole and the cisterna, in fact, it is not just a collection of vesicles, but a slender, dynamic, complexly organized, polarized system.

In the AG, not only the transport of vesicles from the ER to the plasma membrane occurs. There is reverse vesicle transfer. Thus, vacuoles split off from secondary lysosomes and return together with receptor proteins to the trans-AG zone; there is a flow of vacuoles from the trans-zone to the cis-zone of AG, as well as from the cis-zone to the endoplasmic reticulum. In these cases, the vacuoles are coated with proteins of the COP I complex. It is believed that various secondary glycosylation enzymes and receptor proteins in membranes are returned in this way.

Features of the behavior of transport vesicles served as the basis for the hypothesis that there are two types of transport of AG components (Fig. 186).

According to the first type, AG contains stable membrane components to which substances are relayed from the ER by transport vacuoles. According to another type, AG is a derivative of the ER: membrane vacuoles split off from the transition zone of the ER merge with each other into a new cis-tank, which then moves through the entire AG zone and finally breaks up into transport vesicles. According to this model, retrograde COP I vesicles return resident Ag proteins to younger cisternae.

Golgi apparatus

The endoplasmic reticulum, plasma membrane and Golgi apparatus constitute a single membrane system of the cell, within which processes of protein and lipid exchange occur using directed and regulated intracellular membrane transport.
Each of the membrane organelles is characterized by a unique composition of proteins and lipids.

AG structure

AG consists of a group of flat membrane bags - tanks, collected in piles - dictyosomes(~5-10 cisternae, in lower eukaryotes >30). The number of dictyosomes in different cells ranges from 1 to ~500.
The individual cisternae of the dictyosome are of variable thickness - in the center of its membrane they are close together - the lumen is 25 nm, expansions are formed at the periphery - ampoules whose width is not constant. From the ampoules, ~50 nm-1 µm bubbles emerge, connected to the cisterns by a network of tubes.

In multicellular organisms, the AG consists of stacks of tanks interconnected into a single membrane system. AG is a hemisphere, the base of which faces the core. Yeast AG is represented by isolated single tanks surrounded by small vesicles, a tubular network, secretory vesicles and granules. The yeast Sec7 and Sec14 mutants exhibit a structure resembling a stack of mammalian cell cisternae.
AG is characterized by the polarity of its structures. Each stack has two poles: proximal pole(forming, cis-surface) and distal(mature,
trans-surface). Cis pole– the side of the membrane with which bubbles merge. Trans-pole– the side of the membrane from which the vesicles bud.

Five functional compartments of AG:
1. Intermediate vesicular-tubular structures (VTC or ERGIC - ER-Golgi intermediate compartment)
2. Cis-tank (cis) - tanks located closer to the ER:
3. Medial tanks - central tanks
4. Trans tank (trans) - the tanks most distant from the ER.
5. Tubular network adjacent to the transcistern - trans-Golgi network (TGN)
The cisternae stacks are curved so that the concave transsurface faces the core.
On average, there are 3-8 cisterns in AG; there may be more in actively secreting cells (up to 13 in exocrine cells of the pancreas).
Each tank has cis and trans surfaces. Synthesized proteins, membrane lipids, glycosylated in the ER, enter the AG through the cis pole. Substances are transferred through the stacks by transport
bubbles separating from the ampoules. As proteins or lipids pass through the Golgi stacks, they undergo a series of post-translational modifications, including changes to N-linked oligosaccharides:
cis: Mannosidase I trims long mannose chains to M-5
intermediate: N-acetylglucoamine transferase I transfers N-acetylglucosamine
trance: terminal sugars are added - galactose residues and sialic acid.

Structure of the Golgi Apparatus and transport scheme.

Five components of AG and transport scheme: intermediate (ERGIC), cis, intermediate, trans and trans Golgi network (TGN). 1. Entry of synthesized proteins, membrane glycoproteins and lysosomal enzymes into the transitional ER tank adjacent to the AG and 2 - their exit from the ER in vesicles bordered by COPI (anterograde transport). 3 - possible transport of cargo from tubulo-vesicular
clusters to the cis-cistern of AG in COPI vesicles; 3* - transport of cargo from earlier to later tanks; 4 - possible retrograde vesicular transport of cargo between AG tanks; 5 - return of resident proteins from AG to tER using vesicles bordered by COPI (retrograde transport); 6 and 6* - transfer of lysosomal enzymes using clathrin-lined vesicles, respectively, into early EE and late LE endosomes; 7 - regulated secretion of secretory granules; 8 - constitutive integration of membrane proteins into the apical plasma membrane of the PM; 9 - receptor-mediated endocytosis using clathrin-lined vesicles; 10 return of a number of receptors from early endosomes to the plasma membrane; 11 - transport of ligands from EE to LE and Lysosomes; 12 - transport of ligands in non-clathrin vesicles.

AG functions

1. Transport- three groups of proteins pass through the AG: proteins of the periplasmic membrane, proteins intended
for export from the cell, and lysosomal enzymes.
2. Sorting for transport: sorting for further transport to organelles, PM, endosomes, secretory vesicles occurs in the trans-Golgi complex.
3. Secretion- secretion of products synthesized in the cell.
3. Glycosylation proteins and lipids: glycosidases remove sugar residues - deglycosylation, glycosyltransferases attach sugars back to the main carbohydrate chain - glycosylation. It involves glycosylation of oligosaccharide chains of proteins and lipids, sulfation of a number of sugars and tyrosine residues of proteins, as well as activation of precursors of polypeptide hormones and neuropeptides.
4. Synthesis of polysaccharides- many polysaccharides are formed in AG, including pectin and hemicellulose, which form the cell walls of plants and most glycosaminoglycans forming the intercellular matrix in animals

5. Sulfation- most sugars added to the protein core of a proteoglycan are sulfated
6. Addition of Mannose 6-Phosphate: M-6-P is added as a signal to enzymes destined for lysosomes.

GLYCOSYLATION
Most proteins begin to be glycosylated in the rough ER by the addition of N-linked oligosaccharides to the growing polypeptide chain. If the glycoprotein is folded in the desired conformation, it leaves the ER and goes to the AG, where its post-translational modification occurs.
Enzymes - glycosyltransferases - take part in the glycosylation of secreted products. They are involved in the remodeling of T-linked oligosaccharide side chains and the addition of O-linked glycans and oligosaccharide parts of glycolipid proteoglycans. The α-mannosidase enzymes I and II, which are also resident AG proteins, participate in the modification of oligosaccharides.

In addition, glycosylation of lipid-protein membrane domains called rafts occurs in AG.
Dolichol phosphate adds a carbohydrate complex - 2GlcNAc-9-mannose-3-glucose to the asparagine of the growing polypeptide. Terminal glucose is cleaved in two stages: glucosidase I cleaves off the terminal glucose residue, glucosidase II removes two more glucose residues. Then mannose is split off. At this point, the initial stage of carbohydrate processing in the ER is completed and proteins carrying the oligosaccharide complex enter the AG
In the first AG tanks, three more mannose residues are removed. At this stage, the core complex has 5 more mannose residues. N-acetylglucosamine transferase I adds one N-acetylglucosamine residue GlcNAc. Three more mannose residues are cleaved from the resulting complex. Now consists of two molecules GlcNAc-3-mannose-1-GlcNAc is the core structure to which other glycosyltransferases add
carbohydrates. Each glycosyltransferase recognizes the developing carbohydrate structure and adds its own saccharide to the chain.

SECRETION
Secretion pattern:
Proteins synthesized in the ER are concentrated at the exit sites of the transitional ER due to the activity of the coatomeric complex COPII and accompanying components and are transported to the ERGIC compartment intermediate between the ER and AG, from which they pass to the AG in budding vesicles or along tubular structures. Proteins are covalently modified as they pass through the AG cisterns and are sorted on the trans surface of the AG and sent to their destinations. Secretion of proteins requires the passive incorporation of new membrane components into the plasma membrane. To restore membrane balance, constitutive receptor-mediated endocytosis is used.
The endo and exocytotic pathways of membrane transport have common patterns in the direction of movement of membrane transporters to the corresponding
targets and in the specificity of fusion and budding. The main meeting point of these paths is the AG.

Presented flattened tanks(or bags) collected in a stack. Each tank is slightly curved and has convex and concave surfaces. The average diameter of the tanks is about 1 micron. In the center of the tank, its membranes are brought closer together, and at the periphery they often form expansions, or ampoules, from which the bubbles are detached. Packets of flat tanks with an average number of about 5-10 form a dictyosome. In addition to the cisternae, the Golgi complex contains transport and secretory vesicles.

IN dictyosome In accordance with the direction of curvature of the curved surfaces of the tanks, two surfaces are distinguished. A convex surface is called an immature or cis surface. It faces the nucleus or the tubules of the granular endoplasmic reticulum and is connected to the latter by vesicles that detach from the granular reticulum and bring protein molecules to the dictyosome for maturation and formation into the membrane.

Opposite transsurface dictyosomes concave. It faces the plasmalemma and is called mature because secretory vesicles containing secretion products ready for removal from the cell emerge from its membranes.

Golgi complex participates in the accumulation of products synthesized in the endoplasmic reticulum, in their chemical restructuring and maturation. In the tanks of the Golgi complex, polysaccharides are synthesized and complexed with protein molecules. One of the main functions of the Golgi complex is the formation of finished secretory products that are removed outside the cell by exocytosis. The most important functions of the Golgi complex for the cell are also the renewal of cell membranes, including areas of the plasmalemma, as well as the replacement of defects in the plasmalemma during the secretory activity of the cell. The Golgi complex is considered the source of the formation of primary lysosomes, although their enzymes are also synthesized in the granular network.

Lysosomes They are intracellularly formed secretory vacuoles filled with hydrolytic enzymes necessary for the processes of phago- and autophagocytosis. At the light-optical level, lysosomes can be identified and the degree of their development in the cell can be judged by the activity of the histochemical reaction to acid phosphatase, a key lysosomal enzyme.

With electron microscopy lysosomes are defined as vesicles limited from the hyaloplasm by a membrane. Conventionally, there are 4 main types of lysosomes: primary and secondary lysosomes, autophagosomes and residual bodies.

Primary lysosomes- these are small membrane vesicles (their average diameter is about 100 nm), filled with homogeneous finely dispersed content, which is a set of hydrolytic enzymes. About 40 enzymes have been identified in lysosomes (proteases, nucleases, glycosidases, phosphorylases, sulfatases), the optimal mode of action of which is designed for an acidic environment (pH 5). Lysosomal membranes contain special carrier proteins for the transport of hydrolytic cleavage products - amino acids, sugars and nucleotides - from the lysosome to the hyaloplasm. The lysosome membrane is resistant to hydrolytic enzymes.

Secondary lysosomes are formed by the fusion of primary lysosomes with endocytic or pinocytotic vacuoles. In other words, secondary lysosomes are intracellular digestive vacuoles, the enzymes of which are supplied by primary lysosomes, and the material for digestion is supplied by the endocytic (pinocytotic) vacuole. The structure of secondary lysosomes is very diverse and changes during the hydrolytic breakdown of the contents. Lysosome enzymes break down biological substances that have entered the cell, resulting in the formation of monomers that are transported through the lysosome membrane into the hyaloplasm, where they are utilized or included in a variety of synthetic and metabolic reactions.

If interaction with primary lysosomes and their own enzymes undergo hydrolytic cleavage of the cell’s own structures (aging organelles, inclusions, etc.), an autophagosome is formed. Autophagocytosis is a natural process in the life of a cell and plays a large role in the renewal of its structures during intracellular regeneration.

Residual bodies this is one of the final stages of the existence of phago- and autolysosomes and is detected during incomplete phago- or autophagocytosis and is subsequently released from the cell by exocytosis. They have compacted contents, and secondary structuring of undigested compounds is often observed (for example, lipids form complex layered formations).

The Golgi complex, or apparatus, is named after the scientist who discovered it. This cellular organelle looks like a complex of cavities bounded by single membranes. In plant cells and protozoa it is represented by several separate smaller stacks (dictyosomes).

Structure of the Golgi apparatus

The Golgi complex, in appearance, visible through an electron microscope, resembles a stack of disc-shaped sacs superimposed on each other, around which there are many vesicles. Inside each “bag” there is a narrow channel, expanding at the ends into so-called tanks (sometimes the entire bag is called a tank). Bubbles bud from them. A system of interconnected tubes is formed around the central stack.

On the outer, somewhat convex-shaped sides of the stack, new cisterns are formed by the fusion of vesicles budding from the smooth one. On the inside of the tank, they complete their maturation and break up again into bubbles. Thus, the Golgi cisterns (stack sacs) move from the outside to the inside.

The part of the complex located closer to the nucleus is called “cis”. The one closest to the membrane is “trans”.

Micrograph of the Golgi complex

Functions of the Golgi complex

The functions of the Golgi apparatus are diverse, in total they come down to modification, redistribution of substances synthesized in the cell, as well as their removal outside the cell, the formation of lysosomes and the construction of the cytoplasmic membrane.

The activity of the Golgi complex is high in secretory cells. Proteins coming from the ER are concentrated in the Golgi apparatus and then transferred to the membrane in the Golgi vesicles. Enzymes are secreted from the cell by reverse pinocytosis.

Oligosaccharide chains are attached to the proteins arriving at the Golgi. In the apparatus, they are modified and serve as markers, with the help of which proteins are sorted and directed along their path.

In plants, during the formation of the cell wall, the Golgi secretes carbohydrates that serve as a matrix for it (cellulose is not synthesized here). The budding Golgi vesicles move with the help of microtubules. Their membranes merge with the cytoplasmic membrane, and the contents are included in the cell wall.

The Golgi complex of goblet cells (located deep in the epithelium of the intestinal mucosa and respiratory tract) secretes the glycoprotein mucin, which forms mucus in solutions. Similar substances are synthesized by cells of the root tip, leaves, etc.

In the cells of the small intestine, the Golgi apparatus performs the function of lipid transport. Fatty acids and glycerol enter the cells. In the smooth ER, the synthesis of its lipids occurs. Most of them are coated with proteins and transported to the cell membrane via the Golgi. After passing through it, the lipids end up in the lymph.

An important function is the formation.

Golgi complex, or Golgi apparatus , - These are single-membrane organelles of eukaryotic cells, the main functions of which are the storage and removal of excess substances from the cells of the body and the formation of lysosomes. These organelles were discovered in 1898 by the Italian physicist C. Golgi.

Structure . Constructed from bags called tanks, tube system And bubbles various sizes. The cisternae of the Golgi complex (CG) are also polar: vesicles with substances that detach from the ER (formation zone) approach one pole, and vesicles with substances separate from the other pole (maturation zone). In cells, the Golgi complex is located mainly near the nucleus. CG is present in all eukaryotic cells, but its structure may differ in different organisms. Thus, in plant cells there are several structural units called dictyosomes. Membranes of the Golgi complex are synthesized granular EPS, adjacent to it. During cell division, the CG breaks down into separate structural units, which are randomly distributed between daughter cells.

Functions . The Golgi complex performs quite diverse and important functions related to the formation and transformation of complex substances. Here are some of them:

1) participation in the construction of biological membranes - for example, in protozoan cells, with the help of its elements, contractile vacuoles, is formed in the sperm acrosomsa;

2 ) formation of lysosomes- hydrolase enzymes synthesized in EPS are packaged into a membrane vesicle, which is separated into the cytoplasm;

3) peroxisome formation- bodies with the catalase enzyme are formed to destroy hydrogen peroxide, which is formed during the oxidation of organic substances and is a toxic composition for cells;

4) synthesis of surface apparatus compounds- lipo-, glyco-, and mucoproteins are formed, which are part of the glycocalyx, cell walls, and mucous capsules;

5) participation in the secretion of substances from the cell- in the CG, the maturation of secretory granules into vesicles occurs, and the movement of these vesicles in the direction of the plasma membrane.

Lysosomes, structure and functions

Lysosomes (from Greek Lysis - dissolution, soma - body) - These are single-membrane organelles of eukaryotic cells that look like round bodies. In unicellular organisms their role is intracellular digestion, in multicellular organisms they perform the function of breaking down substances foreign to the cell. Lysosomes can be located anywhere in the cytoplasm. Lysosomes were discovered by the Belgian cytologist Christian de Duve in 1949.

Structure . Lysosomes have the form of vesicles with a diameter of about 0.5 microns, surrounded by a membrane and filled with hydrolytic enzymes that act in an acidic environment. The enzyme composition of lysosomes is very diverse, it is formed by proteases (enzymes that break down proteins), amylases (enzymes for carbohydrates), lipases (lipid enzymes), nucleases (for the breakdown of nucleic acids), etc. In total, there are up to 40 different enzymes. When the membrane is damaged, enzymes enter the cytoplasm and cause rapid dissolution (lysis) of the cell. Lysosomes are formed by the interaction of CG and granular EPS. Lysosomal enzymes are synthesized in the granular ER and, using vesicles, are transported to the CG located next to the endoplasmic reticulum. Therefore, through the tubular expansion of the CG, enzymes move to its functional surface and are packaged into lysosomes.

Functions . Depending on their functions, different types of lysosomes are distinguished: phagolysosomes, autophagolysosomes, residual bodies, etc. Autophogolysosomes are formed by the fusion of a lysosome with an autophagosome, that is, vesicles containing the cell’s own macromolecular complexes, for example, entire cellular organelles, or their fragments that have lost their functional ability and are subject to destruction. phagolysosomes (phagosomes) are formed by combining lysosomes with phagocytic or pinocytotic vesicles, which contain material captured by the cell for intracellular digestion. The active enzymes in them are in direct contact with biopolymers that are subject to breakdown. Residual bodies- these are undivided particles surrounded by a membrane; they can remain in the cytoplasm for a long time and be utilized here or removed outside the cell by exocytosis. The residual bodies accumulate material, the breakdown of which is difficult (for example, a brown pigment - lipofuscin, which is also called the “aging pigment”). So, the main functions of lysosomes are:

1) autophagy - cleavage of the cell's own components, whole cells or their groups into autophagolysosomes (for example, resorption of the tail of a tadpole, the pectoral gland in adolescents, lysis of liver cells during poisoning)

2) heterophasia- breakdown of foreign substances in phagolysosomes (for example, breakdown of organic particles, viruses, bacteria that have entered the cell in one way or another)

3) digestive function - in unicellular organisms, endosomes fuse with phagocytic vesicles and form a digestive vacuole, which carries out intracellular digestion

4) excretory function- removal of undigested residues from the cell using residual bodies.

BIOLOGY +Storage diseases- hereditary diseases associated with the loss of certain enzymes by lysosomes. The consequence of this loss is the accumulation of undigested substances in the cells, interfering with the normal functioning of the cell. These diseases can be manifested by the development of the skeleton, individual internal organs, the central nervous system, etc. The development of atherosclerosis, obesity, etc. is associated with a deficiency of lysosome enzymes.