In 1898, the Italian scientist C. Golgi, using the properties of binding heavy metals (osmium and silver) with cellular structures, identified mesh formations in nerve cells, which he called the “internal mesh apparatus” (Fig. 174). Further improvement of the metal staining method (impregnation) made it possible to verify that network structures (Golgi apparatus) are found in all cells of any eukaryotic organisms. Typically, the elements of the Golgi apparatus are located near the nucleus, near the cell center (centriole). Areas of the Golgi apparatus, clearly identified by the impregnation method, had the appearance of complex networks in some cells, where the cells were connected to each other or were presented in the form of separate dark areas lying independently of each other (dictyosomes), having the form of rods, grains, concave disks and etc. (Fig. 175). There is no fundamental difference between the reticular and diffuse forms of the Golgi apparatus, since a change in the forms of this organelle is often observed in the same cells. Elements of the Golgi apparatus are often associated with vacuoles, which is especially characteristic of secreting cells.

It was found that the morphology of AG changes depending on the stages of cellular secretion, which served as the basis for D.N. Nasonov (1924) put forward the hypothesis that AG is an organelle that ensures the separation and accumulation of substances in a wide variety of cells.

For a long time, it was not possible to detect elements of the Golgi apparatus in plant cells using conventional microtechnical methods. However, with the advent of electron microscopy, AG elements were discovered in all plant cells, where they are located along the cell periphery.

Fine structure of the Golgi apparatus

An electron microscope shows that the Golgi apparatus is represented by membrane structures collected together in a small zone (Fig. 176, 177). A separate zone of accumulation of these membranes is 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 zone of small smooth vesicles and short membrane cisterns. In samples of preparatively isolated AG zones with negative contrast, it is clear that a network-like or sponge-like system of membrane cavities adjoins the proximal part of the dictyosome. It is believed that this system may represent a 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 side of the cytoplasm - these are pubescent or bordered vesicles of the same type as the bordered vesicles during pinocytosis. This is the so-called trans-Golgi apparatus 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.

When studying thick sections of cells using a megavolt electron microscope, it was found that in cells individual dictosomes can be connected to each other by a system of vacuoles and cisterns. So a loose three-dimensional network is formed, which is visible 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 likely reflects the involvement of microtubules in vacuole movement.

Secretory function of the Golgi apparatus

Membrane elements of AG are involved in the segregation and accumulation of products synthesized in the ER, and participate in their chemical rearrangements and maturation: this is mainly the rearrangement of the oligosaccharide components of glycoproteins in the composition of water-soluble secretions or in the composition of membranes (Fig. 180).

In the AG tanks, the synthesis of polysaccharides occurs, their interaction with proteins, leading to the formation of mucoproteins. But most importantly, with the help of elements of the Golgi apparatus, the process of removing ready-made secretions outside the cell occurs. In addition, AG is a source of cellular lysosomes.

The participation of AG in the processes of excretion of secretory products has been very well studied using the example of exocrine pancreatic cells. These cells are characterized by the presence of a large number of secretory granules (zymogen granules), which are membrane vesicles filled with protein content. The proteins of zymogen granules include various enzymes: proteases, lipases, carbohydrates, nucleases. During secretion, the contents of these zymogen granules are released from the cells into the lumen of the gland, and then flows into the intestinal cavity. Since the main product excreted by pancreatic cells is protein, the sequence of incorporation of radioactive amino acids into different parts of the cell was studied (Fig. 181). For this purpose, animals were injected with tritium-labeled amino acid (3H-leucine) and the localization of the label was monitored over time using electron microscopic autoradiography. It turned out that after a short period of time (3-5 min) the label was localized only in the basal areas of the cells, in areas rich in granular ER. Since the label was included in the protein chain during protein synthesis, it was clear that protein synthesis did not occur either in the AG zone or in the zymogen granules themselves, but it was synthesized exclusively in the ergastoplasm on ribosomes. Somewhat later (after 20-40 minutes), a label other than ergastoplasma was found in the zone of AG vacuoles. Consequently, after synthesis in ergastoplasm, the protein was transported to the AG zone. Even later (after 60 min), the label was already detected in the zone of zymogen granules. Subsequently, the mark could be seen in the lumen of the acini of this gland. Thus, it became clear that AG is an intermediate link between the actual synthesis of the secreted protein and its removal from the cell. The processes of protein synthesis and excretion were also studied in detail in other cells (mammary gland, intestinal goblet cells, thyroid gland, etc.), and the morphological features of this process were studied. 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 can 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, they are transported from cisternae to cisternae into the distal part of the dictyosome by means of small vacuoles 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, forming secretory vacuoles. After this, the secretory vacuoles begin to move towards the cell surface, come into contact with the plasma membrane, with which their membranes fuse, and thus the contents of these vacuoles appear outside the cell. Morphologically, this process of extrusion (throwing out) resembles pinocytosis, only with the reverse sequence of stages. It's called exocytosis.

This description of events is only a general diagram of the participation of the Golgi apparatus in secretory processes. the matter is complicated by the fact that the same cell can participate in the synthesis of many secreted proteins, can isolate them from each other and direct them to the cell surface or into lysosomes. In the Golgi apparatus, there is not just a “pumping” of products from one cavity to another, but also their gradual “maturation”, modification of proteins, which ends with the “sorting” of products sent either to lysosomes, or to 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 there. Ultimately, all proteins there have the same oligosaccharide chains, consisting of two molecules of N-acetylglucosamine, six molecules of mannose (Fig. 182). In cis-cisternae, secondary modification of oligosaccharide chains begins and their sorting into two classes. As a result, oligosaccharides on hydrolytic enzymes intended for lysosomes (mannose-rich olgosaccharides) are phosphorylated, and oligosaccharides of other proteins sent to secretory granules or to the plasma membrane undergo complex transformations, losing a number of sugars and adding galactose, N-acetylglucosamine and sialic acids .

In this case, a special complex of oligosaccharides appears. Such 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 subject 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).

These data were obtained using completely different methods. Using differential centrifugation, it was possible to obtain separate heavier (cis-) components of the Golgi apparatus and lighter (trans-) components and determine the presence of glycosidases and their products in them. On the other hand, using monoclonal antibodies to various enzymes using electron microscopy, it was possible to localize them directly on cell sections.

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

In the Golgi apparatus of plant cells, the synthesis of cell wall matrix polysaccharides (hemicelluloses, pectins) occurs. In addition, 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, as already mentioned, on the surface of the plasma membrane.

In the Golgi apparatus of animal cells, the synthesis of long unbranched polysaccharide chains of glucosainoglycans occurs. One of them, hyaluronic acid, which is part of the extracellular matrix of connective tissue, contains several thousand repeating disaccharide blocks. Many glycosainoglycans are covalently linked 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 glycosainoglycans and some proteins also occurs in the Golgi apparatus.

Protein sorting in the Golgi apparatus

So, at least three streams of non-cytosolic proteins synthesized by the cell pass through the Golgi apparatus: a stream of hydrolytic enzymes into the lysosome compartment, 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. Therefore, there must be some special mechanism for the spatial separation of these 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. This process has not been fully deciphered, but using the example of the sorting of lysosomal enzymes, one can understand the principle of selection of certain protein molecules (Fig. 184).

It is known that only precursor proteins of lysosomal hydrolases have a specific oligosaccharide, namely a mannose group. In cis cisternae, these groups are phosphorylated and then, together with other proteins, are transferred from cisternae to cisternae, through the middle zone 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. This binding occurs at neutral pH values ​​within the cisternae of the trans network. On membranes, these M-6-F receptor proteins form clusters, groups that are concentrated in the zones of formation of small vesicles coated with clathrin. In the trans-network of the Golgi apparatus, their separation, budding and further transfer to endosomes occur. 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 separated from the trans-network, these vesicles quickly lose their coat, merge with endosomes, transferring their lysosomal enzymes associated with membrane receptors into this vacuole. As already mentioned, acidification of the environment occurs inside endosomes due to the activity of the proton transporter. 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.

Most likely, that part of the proteins that accumulates in secretory vacuoles and is 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. These secretory proteins first enter small vacuoles, also coated with clathrin, which then merge with each other. In secretory vacuoles, accumulated proteins often aggregate in the form of dense secretory granules. This results in an increase in protein concentration in these vacuoles by approximately 200 times compared to its concentration in the Golgi apparatus. Then these proteins, as they accumulate in secretory vacuoles, are released from the cell by exocytosis, when the cell receives the corresponding signal.

The third stream of vacuoles, associated with constant, constitutive secretion, also emanates from the Golgi apparatus. Thus, fibroblasts secrete a large amount of glycoproteins and mucins that are part of the main 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 retrograde transport of vesicles. Thus, vacuoles split off from secondary lysosomes and return, together with receptor proteins, to the trans-AG zone. In addition, there is a flow of vacuoles from the trans zone to the cis zone of the 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.

These features of the behavior of transport vesicles gave rise to the hypothesis that there are two types of transport of AG components (Fig. 186).

According to one of them, the oldest, there are stable membrane components in the AG, to which substances are relayed from the ER using transport vacuoles. According to an alternative model, AG is a dynamic derivative of the ER: membrane vacuoles split off from 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. Thus, it is assumed that the transition zone of the ER represents a “maternity hospital” for the Golgi apparatus.

The Golgi apparatus performs the following functions:

• accumulates proteins, fats and carbohydrates, and then releases them to the cytoplasm, and they are used for the vital processes of the cell itself;
• formation of enzymes (For example, in the pancreas of animals, cells synthesize digestive enzymes);
• synthesis of fats and carbohydrates;
• aids in growth and renewal of the plasma membrane

But Main function of the Golgi complex- excretion of substances synthesized by the cell.

The study of the Golgi apparatus continues, so we are still learning about new functions that nature has assigned to this complex.

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The Golgi apparatus is a stack of flattened membrane sacs (“”) and a system of vesicles associated with them. When studying ultrathin sections, it was difficult to reveal its three-dimensional structure, but scientists suggested that interconnected tubes were formed around the central one.

The Golgi apparatus performs the function of transporting substances and chemical modification of cellular products entering it. This function is especially important in secretory cells, for example, pancreatic acinar cells secrete digestive enzymes of pancreatic juice into the excretory duct. Scientists studied the functioning of the Golgi apparatus using electron micrographs of such a cell. Individual transport of substances was identified using radioactively labeled amino acids.

In a cell, proteins are built from amino acids. It has been established that they are concentrated in the vesicles of the Golgi apparatus and then transported to the plasma membrane. At the final stage, the secretion of inactive enzymes occurs; this form is necessary so that they cannot destroy the cells in which they are formed. Typically, proteins entering the Golgi complex are glycoproteins. There they undergo a modification that turns them into markers that allow the protein to be directed strictly to its intended purpose. Exactly how the Golgi complex distributes molecules has not been precisely established.

Function of carbohydrate secretion

In some cases, the Golgi apparatus takes part in the secretion of carbohydrates, for example, in plants - in the formation of cell wall material. Its activity increases in the region of the cell plate, located between two newly formed daughter nuclei. Golgi vesicles are guided to this site by microtubules. The membranes of the vesicles become part of the plasma membranes of the daughter cells. Their contents become necessary for the construction of cell walls of the middle plate and new walls. Cellulose is supplied separately to cells using microtubules, bypassing the Golgi apparatus.

The Golgi apparatus also synthesizes the glycoprotein mucin, which forms mucus in solution. It is produced by goblet cells, which are located in the thickness of the epithelium of the respiratory tract mucosa and intestinal lining. In some insectivorous plants, the Golgi apparatus produces enzymes and sticky mucus in the leaf glands. The Golgi complex is also involved in the secretion of wax, mucus, gum and plant glue.

The Golgi apparatus is an important organelle that is present in almost every cell. Perhaps the only cells that lack this complex are the red blood cells of vertebrates. The functions of this structure are very diverse. It is in the tanks of the apparatus that all compounds produced by the cell accumulate, after which their further sorting, modification, redistribution and transport occur.

Despite the fact that the Golgi apparatus was discovered back in 1897, to this day some of its functions are being actively studied. Let us consider in more detail the features of its structure and functioning.

Golgi apparatus: structure

This organelle is a collection of membrane cisterns that are closely adjacent to each other, resembling a stack. The structural and functional unit here is considered to be the dictyosome.

The dictyosome is a separate, independent part of the Golgi apparatus, which consists of 3 - 8 cisternae closely adjacent to each other. A stack of these membrane cisterns is surrounded by a system of small vacuoles and vesicles - this is how the transport of substances is carried out, as well as the communication of dictyosomes with each other and other cellular structures. As a rule, they have only one dictyosome, while in plant structures there can be many of them.

In a dictyosome, it is customary to separate two ends - cis and trans sides. The cis side faces the nucleus and the granular endoplasmic reticulum. Synthesized proteins and other compounds are transported here in the form of membrane vesicles. At this end of the dictyosome, new cisternae are constantly formed.

The trans side faces Generally, it is slightly wider. This includes compounds that have already gone through all stages of modification. Small vacuoles and vesicles constantly break off from the lower tank, which transport substances to the desired organelles of the cell.

Golgi apparatus: functions

As already mentioned, the functions of the organelle are very diverse.

• Here, modification of newly synthesized protein molecules is carried out. In most cases, a carbohydrate, sulfate or phosphorus radical is attached to the protein molecule. Thus, the Golgi apparatus is responsible for the formation of protein enzymes and lysosome proteins.
• The Golgi apparatus is responsible for transporting modified proteins to certain areas of the cell. Small bubbles containing ready-made proteins are constantly separated from the trans side.
• Here the formation and transport of all lysosome enzymes occurs.
• In the cavities of the tanks, lipids accumulate, and subsequently the formation of lipoproteins - a complex of protein and lipid molecules.
• The Golgi apparatus of a plant cell is responsible for the synthesis of polysaccharides, which are then used to form the plant, as well as mucus, pectins, hemicellulose and waxes.
• After plant cell division, the Golgi complex takes part in the formation of the cell plate.
• In the sperm, this organelle takes part in the formation of acrosome enzymes, with the help of which the membranes of the egg are destroyed during fertilization.
• In the cells of protozoan representatives, the Golgi complex is responsible for the formation that regulates

Of course, this is not a complete list of all functions performed. Modern scientists are still conducting a wide variety of research using the latest technologies. It is likely that the list of functions of the Golgi complex will grow significantly in the next few years. But today we can say with certainty that this organelle supports the normal functioning of both the cell and the entire organism as a whole.

The Golgi complex consists of a set of flattened cisternae expanded at the edges, stacked and vesicles budding from the cisternae. Each such cluster of cisterns is called a dictyosome. The structure of the Golgi complex depends on the type and functional state of cells. The number of cisternae in different cells varies, most often in the range of 5-12. For example, in the secretory cells of the pancreas, the Golgi complex has many cisterns. The number of dictyosomes in cells also varies. The Golgi complex is usually located between the endoplasmic reticulum and the plasma membrane. The part of the Golgi complex facing the endoplasmic reticulum is called the cis-pole, and the part remote from the ES is called the trans-pole. In accordance with the polarity of the Golgi complex, each side of its cisternae has cis and trans surfaces.

With the help of transport vesicles, the Golgi complex receives proteins from the endoplasmic reticulum. Here they undergo biochemical processing, most of which is the attachment of carbohydrate complexes to proteins and lipids. In addition, the Golgi complex sorts them and, according to their purpose, “packs” them into vesicles, which deliver the contents to lysosomes, peroxisomes, the plasma membrane, and secretory vesicles. The Golgi complex packages proteins intended for secretion into vesicles that migrate towards the plasma membrane. Having reached the plasma membrane, the vesicles merge with the plasma membrane of the cell and release their contents by exocytosis. Some proteins intended for exocytosis can remain in the cytoplasm for a long time, being released under the influence of a specific stimulus. Thus, digestive enzymes in the cells of the pancreas can be stored for a long time in secretory granules, released only when food enters the intestine.

Along with its participation in the processing (maturation) and sorting of proteins secreted by the cell, the formation of lysosomes and secretory granules in secretory cells, the Golgi complex is involved in the hydroosmotic response of the cell. In the case of large water flows, the cytoplasm is flooded, and the water is partially collected in large vacuoles of the Golgi complex.

Rice. Golgi complex. Proteins and lipids enter the Golgi complex from the cis side. Transport bubbles transport these molecules sequentially from one tank to another, where they are sorted. The finished product exits the complex on the trans side, residing in various bubbles. Some of the vesicles containing the protein undergo exocytosis; other vesicles transport proteins for the plasma membrane and lysosomes.

The main types of movement within the cell are the flow of proteins and the flow of bubbles (vesicles). One of the most important tasks of a cell is the delivery of molecules to various parts inside the cell and into the extracellular space. There are strictly defined pathways for intracellular and intercellular movement of material. Although some variation may occur in highly specialized ones, intracellular fluxes in eukaryotic cells are generally similar. For example, although bidirectional flow sometimes occurs between organelles, protein and vesicular flow are predominantly unidirectional—membrane proteins move from the endoplasmic reticulum to the cell surface.

Special proteins also carry out the delivery of substances from one part of the cell to another. Specific polypeptide sequences of these proteins act as signal labels. An important medical discovery over the past two decades has been the understanding that disruption of any of these transport pathways can lead to disease. A defect in a signaling marker or marker recognition locus can significantly impair the health, condition of the cell and the organism. Detailed study of these pathways is essential to understanding the molecular basis of many human diseases.

Lysosomes ( from Greek lysis – decomposition, decay and Greek. soma - body) - membrane-surrounded organelles (0.2-0.8 µm in diameter) present in the cytoplasm of all eukaryotic cells. There are several hundred of them in liver cells. Lysosomes are figuratively called bags with “weapons of mass destruction”, since inside them there is a whole set of hydrolytic enzymes that can destroy any component of the cell. It is not only the lysosomal membrane that saves the cell from destruction. Lysosomal enzymes operate in an acidic environment (pH 4.5), which is maintained within the lysosome by an ATP-dependent proton pump. Primary lysosomes bud from the Golgi apparatus in the form of vesicles filled with enzymes. Objects to be destroyed can initially be located both inside and outside the cell. These can be aged mitochondria, red blood cells, membrane components, glycogen, lipoproteins, etc. Aged mitochondria are recognized and enclosed in a vesicle, which is formed from the membrane of the endoplasmic reticulum. Such bubbles are called autophagosomes. Membrane vesicles containing particles captured from outside are called endosomes. Autophagosomes, phagosomes and endosomes merge with primary lysosomes, where digestion of absorbed particles and substances occurs. The absence of one or more enzymes is fraught with serious diseases.

About 40 lysosomal diseases (storage diseases) are known. All of them are associated with the absence of one or another hydrolytic enzyme in lysosomes. As a result, a significant amount of the substrate of the missing enzyme accumulates inside the lysosomes, either in the form of intact molecules or in the form of partially cleaved residues. Depending on which enzyme is missing, accumulation of glycoproteins, glycogen, lipids, glycolipids, glycosaminoglycans (mucopolysaccharides) may occur. Lysosomes that are excessively filled with one substance or another interfere with the normal performance of cellular functions and, as a result, cause the manifestation of diseases. The molecular mechanisms of lysosomal diseases are caused by mutations of structural genes that control the process of intralysosomal hydrolysis of macromolecules. The mutation may affect the synthesis, processing (maturation) or transport of the lysosomal enzymes themselves.

Peroxisomes- these are vesicles (bubbles) 0.1-1.5 microns in size, which received their name for their ability to form hydrogen peroxide. These membrane vesicles are present in mammalian cells. They are especially numerous in liver and kidney cells. Peroxisomes perform both anabolic and catabolic functions. They contain in the matrix more than 40 enzymes that catalyze anabolic reactions in the biosynthesis of bile acids from cholesterol. They also contain enzymes of the oxidase class. Oxidases use oxygen to oxidize various substrates, and the product of oxygen reduction is not water, but hydrogen peroxide. Hydrogen peroxide, in turn, itself oxidizes other substrates (including some of the alcohol in the epithelial cells of the liver and kidneys). In peroxisomes, some phenols, d-amino acids, as well as fatty acids with very long (more than 22 carbon atoms) chains, which cannot be oxidized in mitochondria before shortening, are oxidized. These fatty acids are found in rapeseed oil. The lifespan of peroxisomes is 5-6 days. New peroxisomes arise from previous peroxisomes by dividing them.

Currently, about 20 human diseases associated with peroxisome dysfunction are known. All of them have neurological symptoms and appear in early childhood. The mode of inheritance of most peroxisomal diseases is autosomal recessive. Peroxisomal diseases can be caused by impaired synthesis of bile acids and cholesterol, impaired synthesis of long-chain and branched-chain fatty acids, polyunsaturated fatty acids, dicarboxylic acids, etc. A rare fatal genetic disease caused by the accumulation of C 24 And C 26 - fatty acids, as well as precursors of bile acids.

Proteasomes – special cellular “factories” for the destruction of proteins. The very name proteasome - (protos - main, primary and soma - body) shows that it is an organelle capable of proteolysis - lysis of proteins. Proteasomes contain a barrel-shaped core of 28 subunits and have a sedimentation coefficient of 20S. (S – Svedberg unit). 20S – proteasome has the shape of a hollow cylinder of 15-17 nm and a diameter of 11-12 nm. It consists of 4 rings of two types lying on top of each other. Each ring contains 7 protein subunits and includes 12-15 polypeptides. There are 3 proteolytic chambers on the inside of the cylinder. Proteolysis (destruction of proteins) occurs in the central chamber and is carried out with the help of protease enzymes. In this chamber, proteins containing transcription errors, toxic or regulatory proteins that have become unnecessary for the cell are broken down. For example, cyclin proteins involved in regulatory processes during cell division.

The marking of unnecessary proteins is carried out by a specific enzyme system - the ubiquitination system. The system attaches the protein ubiquitin (ubique - ubiquitous) to the protein molecule that must be destroyed. Signals for ubiquitination and subsequent degradation can be disturbances in the structure of protein molecules. There is evidence of a connection between some hereditary human diseases (fibrocystic disease, Angelman syndrome) and disturbances in ubiquitination enzyme reactions. Disturbances in the proteasomal protein degradation system are thought to be the cause of some neurodegenerative diseases.

Rice. Schematic structure of the proteasome and proteolytic chambers.

Scheme of degradation of protein molecules in proteasomes