We have already become acquainted with the fact that in the interphase nucleus, unfolded chromosomes are not located chaotically, but are strictly ordered. Such organization of the chromosome in the three-dimensional space of the nucleus is necessary not only for chromosome segregation and separation from neighbors to occur during mitosis, but is also necessary for ordering the processes of chromatin replication and transcription. It can be assumed that in order to carry out these tasks, there must be some kind of framework intranuclear system, which can serve as a unifying basis for all nuclear components - chromatin, nucleolus, nuclear envelope. Such a structure is protein nuclear core or matrix. It is necessary to immediately make a reservation that the nuclear matrix does not represent a clear morphological structure: it is revealed as a separate morphological heterogeneous component upon extraction from the nuclei of almost all areas of chromatin, the bulk of RNA and lipoproteins of the nuclear envelope. From the nucleus, which does not lose its general morphology, remaining a spherical structure, there remains a kind of frame, a skeleton, which is sometimes also called the “nuclear skeleton”.

Components of the nuclear matrix (residual nuclear proteins) were first isolated and characterized in the early 60s. It was found that with sequential treatment of isolated rat liver nuclei with a 2 M NaCI solution and then with DNase, complete dissolution of chromatin occurs, and the main structural elements of the nucleus remain: the nuclear envelope, associated components - nucleomes (nuclear filaments) containing protein and RNA , and nucleoli. It has been hypothesized that chromatin fibrils in native nuclei are attached to these axial protein filaments like a “bottle brush” (see Fig. 67).

Much later (mid-70s) these works were developed and led to the emergence of a mass of new information about non-chromatin proteins of the nuclear core and its role in the physiology of the cell nucleus. At the same time, the term “nuclear matrix” was proposed to denote the residual structures of the nucleus that can be obtained as a result of successive extractions of nuclei with various solutions. What was new in these techniques was the use of nonionic detergents, such as Triton X-100, which dissolve nuclear lipoprotein membranes.

The sequence of processing of isolated nuclei, leading to the production of nuclear matrix preparations enriched with protein, is as follows (see Table 6).

Table 6. Extraction (in %) of nuclear components in the process of obtaining nuclear protein matrix

Isolated nuclei obtained in solutions of 0.25 M sucrose, 0.05 M Tris-HCI buffer and 5 mM MgCI 2 were placed in a solution of low ionic strength (LS), where the bulk of the DNA was degraded due to endonuclease cleavage. In 2 M NaCI (HS), chromatin was subsequently dissociated into histones and DNA, and further extraction of DNA fragments and various proteins took place. Subsequent treatment of nuclei in a 1% Triton X-100 solution led to almost complete loss of nuclear envelope phospholipids and the formation of a nuclear matrix (NM) containing DNA and RNA residues, which were further dissolved by treatment with nucleases, resulting in the final nuclear protein matrix fraction ( NPM). It consists of 98% non-histone proteins; it also contains 0.1% DNA, 1.2% RNA, and 1.1% phospholipids.

The chemical composition of the nuclear matrix obtained in this way is similar in different objects (see Table 7).

Table 7. Composition of the nuclear protein matrix

According to its morphological composition, the nuclear matrix consists of at least three components: a peripheral protein mesh (fibrous) layer - lamina (nuclear lamina, fibrous lamina), an internal or interchromatic network (skeleton) and a “residual” nucleolus (Fig. 68) .

The lamina is a thin fibrous layer underlying the inner membrane of the nuclear envelope. It also includes complexes of nuclear pores, which are, as it were, embedded in the fibrous layer. This part of the nuclear matrix is ​​often called the “pore complex – lamina” fraction (PCL – “pore complex – lamina”). In intact cells and nuclei, lamin is mostly not detected morphologically, because a layer of peripheral chromatin is closely adjacent to it. Only sometimes can it be observed in the form of a relatively thin (10-20 nm) fibrous layer located between the inner membrane of the nuclear envelope and the peripheral layer of chromatin.

The structural role of the lamina is very important: it forms a continuous fibrous protein layer along the periphery of the nucleus, sufficient to maintain the morphological integrity of the nucleus. Thus, the removal of both membranes of the nuclear membrane using Triton X-100 does not cause disintegration or dissolution of the nuclei. They retain their round shape and do not spread out even if they are transferred to low ionic strength when chromatin swelling occurs.

The intranuclear framework or network is morphologically revealed only after chromatin extraction. It is represented by a loose fibrous network located between sections of chromatin; often this spongy network includes various granules of RNP nature.

Finally, the third component of the nuclear matrix is ​​the residual nucleolus - a dense structure that repeats the shape of the nucleolus and also consists of densely packed fibrils.

The morphological expression of these three components of the nuclear matrix, as well as the amount in the fractions, depends on a number of conditions for processing the nuclei. Matrix elements are best identified after isolation of nuclei in relatively high (5 mM) concentrations of divalent cations.

It was found that the formation of disulfide bonds is of great importance for identifying the protein component of the nuclear matrix. So, if the nuclei are pre-incubated with iodoacetamide, which prevents the formation of S-S bonds, and then stepwise extraction is carried out, then the nuclear matrix is ​​represented only by the PCL complex. If we use sodium tetrathionate, which causes the closure of S-S bonds, then the nuclear matrix is ​​represented by all three components. In nuclei pre-treated with hypotonic solutions, only the lamina and residual nucleoli are detected.

All these observations led to the conclusion that the components of the nuclear matrix are not frozen rigid structures, but components with dynamic mobility, which can change not only depending on the conditions of their isolation, but also on the functional characteristics of native nuclei. For example, in mature erythrocytes of chickens, the entire genome is repressed and chromatin is localized mainly at the periphery of the nucleus; in this case, the internal matrix is ​​not detected, but only a lamina with pores. In the erythrocytes of 5-day-old chick embryos, the nuclei of which retain transcriptional activity, the elements of the internal matrix are clearly expressed.

As can be seen from the table. 7, the main component of the residual structures of the nucleus is protein, the content of which can range from 98 to 88%. The protein composition of the nuclear matrix from different cells is quite similar. It is characterized by three proteins of the fibrous layer, called lamins. In addition to these major polypeptides, the matrix contains a large number of minor components with molecular weights from 11-13 to 200 kDa.

Lamins are represented by three proteins (lamins A, B, C). Two of them, lamins A and C, are close to each other immunologically and in peptide composition. Lamin B differs from them in that it is a lipoprotein and therefore binds more tightly to the nuclear membrane. Lamin B remains associated with membranes even during mitosis, while lamins A and C are released upon destruction of the fibrous layer and diffusely distributed throughout the cell.

As it turned out, lamins are similar in their amino acid composition to intermediate microfilaments (vimentin and cytokeratin) that are part of the cytoskeleton. Often, the fraction of isolated nuclei, as well as preparations of the nuclear matrix, contain significant amounts of intermediate filaments, which remain associated with the nuclear periphery even after removal of the nuclear membranes.

Unlike intermediate filaments, lamins do not form filamentous structures during polymerization, but are organized into networks with an orthogonal type of molecular packing. Such continuous lattice areas that underlie the inner membrane of the nuclear envelope can be disassembled during phosphorylation of lamins, and polymerize again when they are dephosphorylated, which ensures the dynamism of both this layer and the entire nuclear envelope.

The molecular characterization of intranuclear core proteins has not yet been developed in detail. It has been shown that it includes a number of proteins that take part in the domain organization of DNA in the interphase nucleus in the creation of a rosette-shaped, chromomeric form of chromatin packaging. The assumption that the elements of the internal matrix represent the cores of the rosette structures of chromomeres is confirmed by the fact that the polypeptide composition of the matrix of interphase nuclei (with the exception of lamina proteins) and the residual structures of metaphase chromosomes (axial structures or “scaffolds”) are almost the same. In both cases, these proteins are responsible for maintaining the loop organization of DNA.

Composed of a peripheral plate and cords penetrating the nucleus. At present, the function of the nuclear skeleton has not been fully elucidated.

It is believed that the matrix is ​​built predominantly from non-histone proteins, forming a complex branched network communicating with the nuclear lamina. Perhaps the nuclear matrix takes part in the formation of functional chromatin domains. In the cell genome there are special insignificant A-T-rich regions of attachment to the nuclear matrix (eng. S/MAR - Matrix/Scaffold Attachment Regions), which are supposed to serve for anchoring chromatin loops on nuclear matrix proteins. However, not all researchers recognize the existence of the nuclear matrix.

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This article lacks links to sources of information. Information must be verifiable, otherwise it may be questioned and deleted. You may edit this article to include links to authoritative sources. This mark... ... Wikipedia

- (karyoplasm, karyolymph, nucleoplasm), the contents of the cell nucleus, filling the space between chromatin, nucleolus and other structures. Contains various enzymes, nucleotides, amino acids and other substances necessary to provide... ... Biological encyclopedic dictionary

nuclear skeleton (matrix)- The supporting structure of the nucleus, composed of a peripheral plate and strands penetrating the nucleus, which have a completely unclear biochemical nature, in specific zones with the nuclear system. contacts chromatin and heterogeneous ribonucleoproteins... ... Technical Translator's Guide

Matrix. See nuclear skeleton. (Source: “English-Russian Explanatory Dictionary of Genetic Terms.” Arefiev V.A., Lisovenko L.A., Moscow: Publishing House VNIRO, 1995) ...

Matrix- * matrix * matrix is ​​the main substance of a number of cellular structures: cytoplasm (hyaloplasm, or cytoplasmic M), organelles (for example, M mitochondria, M plastids) and nuclei (karyolymph, or nuclear M). 2. Basic homogeneous and fine-grained substance... ...

Karyoplasm, karyolymph, nucleoplasm karyoplasm, karyolymph, nucleoplasm, “nuclear juice”. Unstainable (unlike chromatin) ) the contents of the cell nucleus in which chromatin is immersed; after removal of chromatin in K.... ... Molecular biology and genetics. Explanatory dictionary.

Nucleoskeleton, nuclear scaffold (matrix) nuclear skeleton (matrix). The supporting structure of the nucleus, composed of a peripheral plate and strands penetrating the nucleus, which have a completely unclear biochemical nature, in specific zones with... ... Molecular biology and genetics. Explanatory dictionary.

Karyoplasm karyolymph nucleoplasm “nuclear juice”- Karyoplasm, karyolymph, nucleoplasm, “nuclear juice” * karyoplasm, karyolymph, nucleaplasm, “nuclear juice” * karyoplasm or caryoplasm or “nuclear juice” 1. The contents of the cell nucleus, enclosed in the nuclear membrane. 2. Unpaintable (in… … Genetics. Encyclopedic Dictionary

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Cells whose DNA is stained with Hoist blue dye. The central and right cells are in interphase, so the entire nucleus is stained. The cell on the left is in a state of mitosis (anaphase), so its nucleus is not visible, and the DNA is condensed so that ... ... Wikipedia

The nucleus may contain a nuclear skeleton, which helps organize its functions

In previous articles on the site we looked at some nuclear domains And subcompartments, which have a unique composition and functions. Other processes such as DNA replication also occur in the nucleus. It is believed that macromolecular replication and splicing machinery may be associated with specific nuclear structures.

In the early S-phase cycle When synthesis occurs, there are many replication sites in the cell. As synthesis proceeds, they merge, leaving only a few dozen larger sites. These large sites are called DNA replication factories.

The figure below shows the distribution of these factories in various stages of S-phase. Since at any given time the number of replication origins exceeds the number of replication factories, each factory must contain tens or hundreds of replication origins. Similar studies suggest that transcription may also occur in a limited number of sites called transcription factories.

The localization of biosynthetic processes in individual sites suggests the existence of a certain supporting structure in the nucleus. Orderly skeletal structure resembling cytoskeleton, is absent from the kernel. However, some studies suggest the presence of a network-like structure in the nucleus, called the nuclear matrix.

Unlike the cytoskeleton matrix becomes visible only after treating the nucleus with detergents, DNase and solutions of high ionic strength. This treatment removes many components, including almost all DNA and membranes, leaving only insoluble proteins and some RNA. The matrix contains short fibers similar in size to intermediate filaments, actin (but not its fibrillar form) and many other proteins. These components do not organize into larger structures.

Because nuclear matrix It is relatively poorly soluble and difficult to study as a whole. Some researchers believe that the nuclear matrix is ​​an artifactual structure because it becomes visible only after a harsh extraction procedure. However, since many important and complex processes occur in the nucleus that must be carried out with maximum precision, it is possible that there may be some kind of organizing support structure.

Among the possible support functions nuclear structure refers to the organization of the molecular machines of RNA replication, transcription and processing, which are represented by the replisome, the RNA polymerase II-holoenzyme complex and the spliceosome, respectively. Although these large multisubunit complexes have much less mass than chromosomes, they are larger in size than their substrates, nucleic acids.

Research data on the structure of these complexes show that they have a special groove that allows the passage of the nucleic acid chain through the complex. According to many studies, these complexes are attached to a supporting nuclear structure. This means that when replication, transcription and splicing begin, the corresponding molecular machines are fixed and nucleic acids move through them.

DNA replication occurs in a limited number of sites called replication factories.
The DNA is labeled with bromodeoxyuridine (BrdU) and visualized using anti-BrdU antibodies conjugated to a fluorophore.
Photographs of cells at various time intervals after mitosis are presented.
Enzyme factories,
carrying out DNA replication and RNA splicing,
may be associated with the nuclear matrix.

In the interphase nucleus, unfolded chromosomes are not arranged chaotically, but strictly ordered. Such organization of the chromosome in the three-dimensional space of the nucleus is necessary not only so that chromosome segregation and separation from neighbors occur during mitosis, but also for ordering of chromatin replication and transcription processes. It can be assumed that in order to carry out these tasks there must be some kind of frame intranuclear system, which can serve as a unifying basis for all nuclear components - chromatin, nucleolus, nuclear envelope. Such a structure is protein nuclear core, or matrix .

The nuclear matrix does not have a clear morphological structure: it is revealed as a separate morphological heterogeneous component upon extraction from the nuclei of almost all areas of chromatin, the bulk of RNA and lipoproteins of the nuclear envelope. From the nucleus, which does not lose its general morphology, remaining a spherical structure, there remains a kind of frame, a skeleton, sometimes also called the “nuclear skeleton”. The components of the nuclear matrix were first isolated and characterized in the early 60s. The nuclear matrix consists of at least three morphological components:

• peripheral protein mesh (fibrous) layer - lamins,
• internal, or interchromatin matrix,
• "residual" nucleolus.

Lamina is a thin fibrous layer underlying the inner membrane of the nuclear envelope. It also includes complexes of nuclear pores, which are, as it were, embedded in the fibrous layer. This part of the nuclear matrix is ​​often called fraction “pore complex - lamina” (PCL). The structural role of the lamina is very important: it forms a continuous fibrous protein layer along the periphery of the nucleus, sufficient to maintain the morphological integrity of the nucleus.

Intranuclear matrix morphologically detected after chromatin extraction. It is represented by a loose fibrous network located between sections of chromatin. Often this spongy network includes various granules.

Residual nucleolus– a dense structure, repeating the shape of the nucleolus, consists of densely packed fibrils.

Components of the nuclear matrix– these are not frozen rigid structures, they are dynamically mobile and can change depending not only on the conditions of their isolation, but also on the functional characteristics of native nuclei. Main component residual structures of the nucleus - protein, the content of which can range from 98 to 88%. The protein composition of the nuclear matrix from different cells is quite similar. It is characterized by three fibrous layer proteins called lamins. In addition to these main polypeptides, the matrix contains a large number of minor components with a molecular weight from 11 - 13 to 200 thousand. Lamins are represented by three proteins: A, B, C. Lamins A and C are close to each other immunologically and in peptide composition. Lamin B differs from them in that it binds more tightly to integral proteins of the nuclear membrane.

Often, the fraction of isolated nuclei, as well as preparations of the nuclear matrix, contain significant amounts of intermediate filaments that remain associated with the periphery of the nucleus even after removal of the nuclear membranes. Unlike intermediate filaments, lamins do not form filamentous structures during polymerization, but are organized into networks with an orthogonal type of molecular packing. Such continuous lattice-like areas underlie the inner membrane of the nuclear envelope. They can be disassembled when lamins are phosphorylated and polymerized again when they are dephosphorylated, which ensures the dynamism of both this layer and the entire nuclear envelope. The molecular characterization of intranuclear matrix proteins has not been developed in detail. Proteins are responsible for maintaining the loop organization of DNA.

DNA nuclear protein matrix

DNA regions can be located in all three components of the nuclear matrix. Two size groups of DNA fragments were discovered in the nuclear matrix. IN first group included high-molecular fragments with a size of about 10 thousand bp. n., they accounted for only 0.02% of the original amount of DNA. Their number was approximately 100 per haploid set of chromosomes, i.e., there are only 2–3 sites of DNA attachment to the nuclear matrix per chromosome. The fragments were enriched in satellite DNA and associated with the lamina. Functional meaning These sections may consist of ensuring a fixed position of chromosomes in the nucleus by securing their certain sections (centromeres, telomeres) to the lamina. Second group of fragments associated with the matrix, consists of small DNA sections (120 - 140 bp), heterogeneous in sequence. They occur between sections of DNA about 50 kb long. n., which are probably loops of the main mass of chromatin. Functional significance of the second group of these short stretches of DNA may be that they are associated with proteins lying at the cores of rosette-like chromatin structures or at the base of unfolded chromatin DNA loops during its activation.

When studying the kinetics of hydrolysis newly synthesized by DNA nucleases, it was discovered that nuclear matrix associated with DNA replication. Most of the DNA containing the radioactive label is associated with the matrix: over 70% of the newly synthesized DNA was localized in the zone of the internal nuclear matrix. This observation gave reason to believe that initiation and actual DNA replication occur on the nuclear matrix. The DNA fraction associated with the nuclear matrix turned out to be enriched in replication forks. Found in the nuclear matrix DNA polymerase a is the main enzyme of DNA replication. In addition to it, other enzymes of the replication complex (replisomes) are associated with the nuclear matrix: DNA primase, DNA ligase, DNA topoisomerase II. The proteins of the inner nuclear matrix include RNA polymerase II, responsible for the synthesis of messenger RNA. The actual transcribed genes are associated with the nuclear matrix. Transcription complexes are fixed on the nuclear matrix, and transcription itself occurs simultaneously with the movement of template DNA relative to fixed transcription complexes containing RNA polymerase II. In addition to tRNA and its precursors, the nuclear protein matrix contains small nuclear ribonucleoproteins(snRNPs), which are involved in the maturation of messenger RNAs during the splicing process. These RNA particles, sometimes called spliceosomes, are collected in groups, or clusters, associated with proteins of the nuclear matrix. Nuclear matrix elements may be directly involved in transcriptional regulation.

Nuclear matrix

is a system of fibrillar proteins that perform both a structural (skeletal) function and a regulatory one in the processes of replication, transcription, maturation of RNA molecules (processing) and their movement both inside and outside the nucleus.

Karyoplasm is a subsystem of the nuclear apparatus, similar to hyaloplasm. Karyoplasm is the second component of the internal environment of the cell. It creates a specific microenvironment for nuclear structures, providing them with normal conditions for functioning. Due to the presence of pore complexes in the nuclear membrane, karyoplasm interacts with hyaloplasm.

The nuclear structures responsible for storing and transmitting the cell's hereditary information are chromosomes, consisting of deoxyribonucleoproteins. Whole chromosomes are visible only in cells dividing by mitosis. Some chromosomes have secondary constrictions - nucleolar organizers. DNA responsible for rRNA synthesis is localized in them.

Single-membrane organelles

Lysosome is a cellular organelle surrounded by a membrane, in the cavity of which an acidic environment is maintained and many soluble hydrolytic enzymes are located. The lysosome is responsible for the intracellular digestion of macromolecules, including autophagy; the lysosome is capable of secreting its contents during the process of lysosomal exocytosis; The lysosome also participates in some intracellular signaling pathways related to metabolism and cell growth.

Lysosomes were discovered in 1955 by Belgian biochemist Christian de Duve. Lysosomes are found in all mammalian cells, with the exception of red blood cells.

A number of hereditary diseases in humans, called lysosomal storage diseases, are associated with dysfunction of lysosomes.

One of the characteristics of lysosomes is the presence in them of a number of enzymes (acid hydrolases) capable of breaking down proteins, carbohydrates, lipids and nucleic acids. Lysosome enzymes include cathepsins (tissue proteases), acid ribonuclease, phospholipase, etc. In total, the lysosome cavity contains about 60 soluble acid hydrolytic enzymes.

Lysosomes are characterized by an acidic reaction of the internal environment, which ensures optimal functioning of lysosomal hydrolases. Degradation is achieved due to the presence in lysosomes of various degrading enzymes - hydrolases with an optimum action in the acidic region. The main enzyme in lysosomes is acid phosphatase. The lysosome membrane contains ATP-dependent vacuole-type proton pumps. They enrich lysosomes with protons, as a result of which the internal environment of lysosomes has a pH of 4.5-5.0 (while in the cytoplasm the pH is 7.0-7.3). Lysosomal enzymes have a pH optimum of about 5.0, i.e. in the acidic region. At pH values ​​close to neutral, characteristic of the cytoplasm, these enzymes have low activity. Obviously, this serves as a mechanism to protect cells from self-digestion in the event that a lysosomal enzyme accidentally enters the cytoplasm.

There are primary and secondary lysosomes. The former are formed in the region of the Golgi apparatus, they contain enzymes in an inactive state, while the latter contain active enzymes. Typically, lysosomal enzymes are activated when the pH decreases. Among lysosomes, one can also distinguish heterolysosomes (digesting material entering the cell from the outside - through phago- or pinocytosis) and autolysosomes (destructing the cell’s own proteins or organelles). The most widely used classification of lysosomes and their associated compartments is:

Early endosome - endocytic (pinocytotic) vesicles enter it. From the early endosome, receptors that have given up their cargo (due to low pH) return to the outer membrane.

Late endosome - vesicles with material absorbed during pinocytosis and vesicles from the Golgi apparatus with hydrolases enter it from the early endosome. Mannose 6-phosphate receptors return from the late endosome to the Golgi apparatus.

Lysosome - vesicles with a mixture of hydrolases and digestible material enter it from the late endosome.

Phagosome - larger particles (bacteria, etc.) enter it and are absorbed by phagocytosis. Phagosomes usually fuse with a lysosome.

Autophagosome is a region of cytoplasm surrounded by two membranes, usually including some organelles and formed during macroautophagy. Fuses with the lysosome.

Multivesicular bodies - usually surrounded by a single membrane, contain inside smaller vesicles surrounded by a single membrane. They are formed by a process reminiscent of microautophagy, but contain material obtained from the outside. In small vesicles, outer membrane receptors (for example, epidermal growth factor receptors) usually remain and are then degraded. The stage of formation corresponds to early endosomes.

Residual bodies (telolysosomes) are vesicles containing undigested material (particularly lipofuscin). In normal cells, they merge with the outer membrane and leave the cell by exocytosis. They accumulate with aging or pathology.

The functions of lysosomes are:

digestion of substances or particles captured by the cell during endocytosis (bacteria, other cells)

autophagy - the destruction of structures unnecessary for the cell, for example, during the replacement of old organelles with new ones, or the digestion of proteins and other substances produced within the cell itself

Autolysis is the self-destruction of a cell that occurs as a result of the release of the contents of lysosomes. Normally, autolysis occurs during metamorphosis (disappearance of the tail in a tadpole of frogs), involution of the uterus after childbirth, and in areas of tissue necrosis.

Some rare diseases are associated with genetic defects in lysosomal enzymes, as these enzymes are involved in the degradation of glycogen (glycogenoses), lipids (lipidoses) and proteoglycans (mucopolysaccharidoses). Products that cannot participate in metabolism due to defects or lack of appropriate enzymes accumulate in residual bodies, which leads to irreversible cell damage and, as a result, dysfunction of the corresponding organs.

Peroxisome

An obligatory organelle of a eukaryotic cell, bounded by a membrane, containing a large number of enzymes that catalyze redox reactions (D-amino acid oxidases, urate oxidases and catalases). It has a size of 0.2 to 1.5 microns, separated from the cytoplasm by a single membrane.

The set of functions of peroxisomes differs in different types of cells. Among them: oxidation of fatty acids, photorespiration, destruction of toxic compounds, synthesis of bile acids, cholesterol, as well as the construction of the myelin sheath of nerve fibers, etc. Along with mitochondria, peroxisomes are the main consumers of O2 in the cell.

The peroxisome usually contains enzymes that use molecular oxygen to abstract hydrogen atoms from certain organic substrates () to form hydrogen peroxide ():

Catalase uses the product to oxidize a variety of substrates - for example, phenols, formic acid, formaldehyde and ethanol:

This type of oxidative reactions is especially important in liver and kidney cells, whose peroxisomes neutralize many toxic substances that enter the bloodstream. Almost half of the ethanol entering the human body is oxidized to acetaldehyde in this way. In addition, the reaction has implications for the detoxification of the cell from hydrogen peroxide itself.

The lifespan of peroxisomes is insignificant - only 5-6 days. New organelles are most often formed as a result of the division of previous ones, like mitochondria. They, however, can also form de novo from the endoplasmic reticulum.

All enzymes located in the peroxisome must be synthesized on ribosomes outside it. To transport them from the cytosol into the organelles, the membranes of peroxisomes have a selective transport system. Discovered by the Belgian cytologist Christian de Duve in 1965.

The Golgi apparatus is a component of all eukaryotic cells (almost the only exception is mammalian red blood cells). It is the most important membrane organelle that controls intracellular transport processes. The main functions of the Golgi apparatus are the modification, accumulation, sorting and direction of various substances into the appropriate intracellular compartments, as well as outside the cell. It consists of a set of flattened tanks surrounded by a membrane, resembling a stack of plates. Associated with Golgi stacks are always a mass of small (approximately 60 nm in diameter) membrane-bound vesicles. Many vesicles are ringed and coated with clathrin or another specific protein. The Golgi apparatus has two different sides: the nascent or cis side and the mature or trans side. The cis side is closely associated with ER transition elements; the trans side expands to form a tubular reticulum called the trans Golgi reticulum. Proteins and lipids in small vesicles enter the Golgi stack from the cis side and leave it, going to various compartments, along with vesicles formed on the trans side. Moving from one Golgi stack to another, these molecules undergo a successive series of modifications.

A well-developed Golgi apparatus is present not only in secretory cells, but also in almost all cells of eukaryotic organisms.

Functions

• 1) sorting, accumulation and removal of secretory products;
• 2) completion of post-translational modification of proteins (glycosylation, sulfation, etc.);
• 3) accumulation of lipid molecules and formation of lipoproteins;
• 4) formation of lysosomes;
• 5) synthesis of polysaccharides for the formation of glycoproteins, waxes, gums, mucus, substances of the matrix of plant cell walls (hemicellulose, pectins), etc.
• 6) formation of a cell plate after nuclear division in plant cells;
• 7) participation in the formation of the acrosome;
• 8) formation of contractile vacuoles of protozoa.

In the Golgi Complex there are 3 sections of cisterns surrounded by membrane vesicles:

Cis section (closest to the nucleus);

Medial department;

Trans department (furthest from the core).

These sections differ from each other in the set of enzymes. In the cis department, the first tank is called the “rescue tank”, since with its help the receptors coming from the intermediate endoplasmic reticulum return back. Enzyme of the cis department: phosphoglycosidase (adds phosphate to the carbohydrate - mannose). In the medial section there are 2 enzymes: mannasidase (cleaves off mannase) and N-acetylglucosamine transferase (adds certain carbohydrates - glycosamines). In the trans section there are enzymes: peptidase (carries out proteolysis) and transferase (carries out the transfer of chemical groups).

The Golgi apparatus is asymmetrical - cisterns located closer to the cell nucleus (cis-Golgi) contain the least mature proteins; membrane vesicles are continuously attached to these cisterns - vesicles budding from the granular endoplasmic reticulum (ER), on the membranes of which protein synthesis by ribosomes occurs . The return of proteins from the Golgi apparatus to the ER requires the presence of a specific signal sequence (lysine-asparagine-glutamine-leucine) and occurs due to the binding of these proteins to membrane receptors in the cis-Golgi.

In the cisterns of the Golgi apparatus, proteins intended for secretion, transmembrane proteins of the plasma membrane, lysosome proteins, etc. mature. The maturing proteins sequentially move through the cisterns to the organelles in which their modifications occur - glycosylation and phosphorylation. In O-glycosylation, complex sugars are added to proteins via an oxygen atom. Phosphorylation occurs when an orthophosphoric acid residue is added to proteins. Maturing proteins are “marked” with special polysaccharide residues (mainly mannose), apparently playing the role of a kind of “quality mark”.

Transport of proteins from the Golgi apparatus

Eventually, vesicles containing fully mature proteins bud from the trans-Golgi. The main function of the Golgi apparatus is the sorting of proteins passing through it. In the Golgi apparatus, the formation of a “tridirectional protein flow” occurs:

maturation and transport of plasma membrane proteins;

maturation and transport of secretions;

maturation and transport of lysosome enzymes.

With the help of vesicular transport, proteins passing through the Golgi apparatus are delivered “to the address” depending on the “tags” they received in the Golgi apparatus.

Lysosome formation

Many hydrolytic enzymes of lysosomes pass through the Golgi apparatus, where they receive a “tag” in the form of a specific sugar - mannose-6-phosphate (M6P) - as part of an oligosaccharide attached to the amino acid chain. The addition of this label occurs with the participation of two enzymes. The enzyme N-acetylglucosamine phosphotransferase specifically recognizes lysosomal hydrolases by details of their tertiary structure and attaches N-acetylglucosamine phosphate to the sixth atom of several mannose residues of the hydrolase oligosaccharide. The second enzyme, phosphoglycosidase, cleaves off N-acetylglucosamine, creating the M6P tag. This label is then recognized by the M6P receptor protein, with its help hydrolases are packaged into vesicles and delivered to lysosomes. There, in an acidic environment, the phosphate is cleaved from the mature hydrolase.

Transport of proteins to the outer membrane

As a rule, even during synthesis, outer membrane proteins are integrated with their hydrophobic regions into the membrane of the endoplasmic reticulum. Then, as part of the vesicle membrane, they are delivered to the Golgi apparatus, and from there to the cell surface. When a vesicle merges with the plasmalemma, such proteins remain in its composition and are not released into the external environment, like those proteins that were in the cavity of the vesicle.