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Golgi complex composition. Cell structure

This part of a living cell was named after the famous scientist from Italy who was engaged in research and discovery. The complex can be of various forms and includes several cavities located in the membranes. Its main goal is to form lysosomes and synthesize various substances, directing them to the endoplasmic reticulum.

Apparatus structure

This part of the cell is also called the Golgi complex, which is a single-membrane eukaryotic organelle. This complex is responsible for the functioning and creation of new lysosomes in the cell, as well as for the preservation of many vital substances that come out of human or animal cells.

In its structure or design, the Golgi apparatus resembles small sacs; in medicine they are also called cisterns, which consist of vesicles of various shapes and the whole system cell tubes. The sacs of the apparatus are considered polar, since at one pole there are bubbles with a special substance that open in the formation zone (EPS), and at the other part of the pole bubbles are formed that separate in the maturing zone. The Golgi cell complex is localized near the nucleus itself and is then distributed throughout all eukaryotes. At the same time, the structure and structure of the apparatus is different, everything depends on the organism in which it is located.

For example, if we talk about plant cells, then they secrete dictyosomes - these are structural units. The shells of this device are created by granular EPS, which is adjacent to it. During the period of cell division, the complex breaks up into single structures; they spread in a chaotic manner and pass into daughter cells.

Characteristics

The main properties of the device are:

What functions does the complex perform?

The roles of this complex are interesting and diverse in their own way. Biologists include the following among such functions:

secretory components are sorted and accumulated to the required amount, after which the device removes them
formation of new lysosomes
accumulation of lipid molecules and development of lipoproteins
post-translational modification of various proteins necessary for cell function
synthesis of polysaccharides for the development of gums, glycoproteins, mucus, waxes and matrix substances responsible for the structure of the wall cells of a plant, animal or human
takes an active part in the formation of acrosomes
responsible for the formation of the simplest contractile vacuoles
after nuclear division occurs, a cell plate is formed

This is not a description of all the functions for which the Golgi complex is responsible. Until now, long-term studies have revealed new advantages and less significant functions of the Golgi complex; today, the transport function of the apparatus and protein synthesis are being carefully studied.

What are lysosomes and their function?

Since the Golgi apparatus is the primary source for the formation of lysosomes, you should pay attention to what lysosomes are and how they function.

Lysosomes are very small cell elements, approximately one micrometer in diameter. The lysosome has three layers of membrane on its surface, inside which there are many different enzymes. These enzymes in the body are responsible for the breakdown of vital important elements. Each individual cell contains up to ten lysosomes, and new ones are already being formed thanks to the Golgi apparatus.

To study cell development, we first need to identify lysosomes and test their response to phosphatase.

Function of lysosomes:

Autophagy is a process by which whole cells, some of their components and their subtypes are slowly broken down. These include: the pancreas, especially at the time adolescence, liver lysis during poisoning.
Excretory system. Lysosomes are responsible for removing undigested food from the cell.
From the outside gastrointestinal tract. Lysosomes and endosomes combine with vesicles of the phagocytic type and thereby form a digestive vacuole, resulting in intracellular digestion.
It is impossible not to mention heterophasia. She is responsible for viruses and others organic matter, which independently fall different ways inside the cell.

The structure known today as complex or Golgi apparatus (AG) first discovered in 1898 by the Italian scientist Camillo Golgi

It was possible to study the structure of the Golgi complex in detail much later using an electron microscope.

AG are stacks of flattened “cisterns” with widened edges. Associated with them is a system of small single-membrane vesicles (Golgi vesicles). Each stack usually consists of 4–6 “tanks”, is a structural and functional unit of the Golgi apparatus and is called a dictyosome. The number of dictyosomes in a cell ranges from one to several hundred.

The Golgi apparatus is usually located near cell nucleus, near the ER (in animal cells, often near the cell center).

Golgi complex

On the left - in a cell, among other organelles.

On the right is the Golgi complex with membrane vesicles separating from it.

All substances synthesized in EPS membranes transferred to Golgi complex V membrane vesicles, which bud from the ER and then merge with the Golgi complex. Organic substances received from EPS undergo further biochemical transformations, accumulate, and are packaged into membrane vesicles and are delivered to those places in the cell where they are needed. They participate in the completion cell membrane or stand out ( secreted) from the cell.

Functions of the Golgi apparatus:

1 Participation 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.

2) Secretory - the formation of finished secretory products that are removed outside the cell by exocytosis.

3) Renewal of cell membranes, including areas of the plasmalemma, as well as replacement of plasmalemma defects in the process secretory activity cells.

4) Place of formation of lysosomes.

5) Transport of substances

Lysosomes

The lysosome was discovered in 1949 by C. de Duve ( Nobel Prize for 1974).

Lysosomes- single-membrane organelles. They are small bubbles (diameter from 0.2 to 0.8 microns) containing a set of hydrolytic enzymes - hydrolases. A lysosome can contain from 20 to 60 various types hydrolytic enzymes (proteinases, nucleases, glucosidases, phosphatases, lipases, etc.) that break down various biopolymers. The breakdown of substances using enzymes is called lysis (lysis-decay).

Lysosome enzymes are synthesized on the rough ER and move to the Golgi apparatus, where they are modified and packaged into membrane vesicles, which, after separation from the Golgi apparatus, become lysosomes themselves. (Lysosomes are sometimes called the "stomachs" of the cell)

Lysosome - membrane vesicle containing hydrolytic enzymes

Functions of lysosomes:

1. Breakdown of substances absorbed as a result of phagocytosis and pinocytosis. Biopolymers are broken down into monomers, which enter the cell and are used for its needs. For example, they can be used to synthesize new organic substances or can be further broken down to produce energy.

2. Destroy old, damaged, redundant organelles. Destruction of organelles can also occur during cell starvation.

3. Carry out autolysis (self-destruction) of cells (liquefaction of tissues in the area of inflammation, destruction of cartilage cells in the process of formation bone tissue and etc.).

Autolysis - This self-destruction cells resulting from the release of contents lysosomes inside the cell. Due to this, lysosomes are jokingly called "suicide instruments". Autolysis is normal phenomenon ontogenesis, it can spread both to individual cells and to the entire tissue or organ, as occurs during the resorption of the tadpole’s tail during metamorphosis, i.e., when the tadpole transforms into a frog

Endoplasmic reticulum, Golgi apparatus and lysosomesform single vacuolar cell system, individual elements of which can transform into each other during restructuring and changing the function of membranes.

Mitochondria

Mitochondria structure:
1 - outer membrane;
2 - internal membrane; 3 - matrix; 4 - crista; 5 - multienzyme system; 6 - circular DNA.

Mitochondria can be rod-shaped, round, spiral, cup-shaped, or branched in shape. The length of mitochondria ranges from 1.5 to 10 µm, diameter - from 0.25 to 1.00 µm. The number of mitochondria in a cell can reach several thousand and depends on the metabolic activity of the cell.

Mitochondria limited two membranes . Outer membrane mitochondria are smooth, the inner forms numerous folds - cristas. Cristae increase the surface area of the inner membrane. The number of cristae in mitochondria can vary depending on the energy needs of the cell. It is on the inner membrane that numerous enzyme complexes involved in the synthesis of adenosine triphosphate (ATP) are concentrated. Here the energy of chemical bonds is converted into energy-rich (macroergic) ATP bonds . Besides, breakdown takes place in mitochondria fatty acids and carbohydrates with the release of energy, which is accumulated and used for the processes of growth and synthesis.The internal environment of these organelles is called matrix. It contains circular DNA and RNA, small ribosomes. Interestingly, mitochondria are semi-autonomous organelles, since they depend on the functioning of the cell, but at the same time they can maintain a certain independence. Thus, they are able to synthesize their own proteins and enzymes, as well as reproduce independently (mitochondria contain their own DNA chain, which contains up to 2% of the DNA of the cell itself).

Functions of mitochondria:

1. Conversion of the energy of chemical bonds into macroergic bonds of ATP (mitochondria are the “energy stations” of the cell).

2. Participate in the processes of cellular respiration - oxygen breakdown of organic substances.

Ribosomes

Ribosome structure:
1 - large subunit; 2 - small subunit.

Ribosomes - non-membrane organelles, approximately 20 nm in diameter. Ribosomes consist of two fragments - large and small subunits. Chemical composition ribosomes - proteins and rRNA. rRNA molecules make up 50–63% of the mass of the ribosome and form its structural framework.

During protein biosynthesis, ribosomes can “work” individually or combine into complexes - polyribosomes (polysomes). In such complexes they are linked to each other by one mRNA molecule.

Ribosomal subunits are formed in the nucleolus. Having passed through the pores in the nuclear envelope, ribosomes enter the membranes of the endoplasmic reticulum (ER).

Function of ribosomes: assembly of a polypeptide chain (synthesis of protein molecules from amino acids).

Cytoskeleton

The cellular cytoskeleton is formed microtubules And microfilaments .

Microtubules are cylindrical formations with a diameter of 24 nm. Their length is 100 µm-1 mm. The main component is a protein called tubulin. It is incapable of contraction and can be destroyed by colchicine.

Microtubules are located in the hyaloplasm and perform the following functions:

· create an elastic, but at the same time durable frame of the cell, which allows it to maintain its shape;

· take part in the process of distribution of cell chromosomes (form a spindle);

· provide movement of organelles;

Microfilaments- threads that are placed under plasma membrane and consist of the protein actin or myosin. They can contract, resulting in movement of the cytoplasm or protrusion of the cell membrane. In addition, these components take part in the formation of the constriction during cell division.

Cell center

The cellular center is an organelle consisting of 2 small granules - centrioles and a radiant sphere around them - the centrosphere. The centriole is a cylindrical body 0.3-0.5 µm long and about 0.15 µm in diameter. The walls of the cylinder consist of 9 parallel tubes. Centrioles are arranged in pairs at right angles to each other. The active role of the cell center is revealed during cell division. Before cell division, centrioles diverge to opposite poles, and a daughter centriole appears near each of them. They form a fission spindle, which contributes to uniform distribution genetic material between daughter cells.

Centrioles are self-replicating organelles of the cytoplasm; they arise as a result of duplication of existing centrioles.

Functions:

1. Ensuring uniform divergence of chromosomes to the poles of the cell during mitosis or meiosis.

2. Center for cytoskeletal organization.

Organoids of movement

Not present in all cells

Organelles of movement include cilia and flagella. These are miniature growths in the form of hairs. The flagellum contains 20 microtubules. Its base is located in the cytoplasm and is called the basal body. The length of the flagellum is 100 µm or more. Flagella, which are only 10-20 microns, are called eyelashes . When microtubules slide, cilia and flagella are able to vibrate, causing the cell itself to move. The cytoplasm may contain contractile fibrils called myofibrils. Myofibrils are usually located in myocytes - cells muscle tissue, as well as in heart cells. They consist of smaller fibers (protofibrils).

In animals and humans cilia they cover the airways Airways and help get rid of small solid particles, such as dust. In addition, there are also pseudopods that provide amoeboid movement and are elements of many unicellular and animal cells (for example, leukocytes).

Functions:

Specific

Core. Chromosomes

Structure and functions of the nucleus

Typically, a eukaryotic cell has one core, but there are binucleate (ciliates) and multinucleate cells (opaline). Some highly specialized cells lose their nucleus for the second time (erythrocytes of mammals, sieve tubes of angiosperms).

The shape of the core is spherical, ellipsoid, less often lobed, bean-shaped, etc. The diameter of the core is usually from 3 to 10 microns.

Core structure:
1 - outer membrane; 2 - internal membrane; 3 - pores; 4 - nucleolus; 5 - heterochromatin; 6 - euchromatin.

Core separated from the cytoplasm by two membranes (each of them has typical structure). Between the membranes there is a narrow gap filled with a semi-liquid substance. In some places, the membranes merge with each other, forming pores through which the exchange of substances occurs between the nucleus and the cytoplasm. The outer nuclear membrane on the side facing the cytoplasm is covered with ribosomes, giving it roughness; the inner membrane is smooth. Nuclear membranes are part of the cell membrane system: outgrowths of the outer nuclear membrane connect to the channels of the endoplasmic reticulum, forming unified system communicating channels.

Karyoplasm (nuclear juice, nucleoplasm)- the internal contents of the kernel, in which they are located chromatin and one or more nucleoli. Nuclear juice contains various proteins (including nuclear enzymes), free nucleotides.

Nucleolus It is a round, dense body immersed in nuclear juice. The number of nucleoli depends on functional state nuclei and varies from 1 to 7 or more. Nucleoli are found only in non-dividing nuclei; they disappear during mitosis. The nucleolus is formed on certain sections of chromosomes that carry information about the structure of rRNA. Such regions are called the nucleolar organizer and contain numerous copies of genes encoding rRNA. Ribosomal subunits are formed from rRNA and proteins coming from the cytoplasm. Thus, the nucleolus is a collection of rRNA and ribosomal subunits at different stages of their formation.

Chromatin- internal nucleoprotein structures of the nucleus, stained with certain dyes and differing in shape from the nucleolus. Chromatin has the form of clumps, granules and threads. Chemical composition of chromatin: 1) DNA (30–45%), 2) histone proteins (30–50%), 3) non-histone proteins (4–33%), therefore, chromatin is a deoxyribonucleoprotein complex (DNP). Depending on the functional state of chromatin, there are: heterochromatin And euchromatin .

Euchromatin- genetically active, heterochromatin - genetically inactive areas of chromatin. Euchromatin is not distinguishable under light microscopy, is weakly stained and represents decondensed (despiralized, untwisted) sections of chromatin. Heterochromatin under a light microscope it looks like clumps or granules, is intensely stained and represents condensed (spiralized, compacted) areas of chromatin. Chromatin is the form of existence of genetic material in interphase cells. During cell division (mitosis, meiosis), chromatin is converted into chromosomes.

Kernel functions:

1. Storage of hereditary information and transmission of it to daughter cells during division.

2. Control of the process of protein biosynthesis.

3. Regulation of cell division and body development processes.

4. Place of formation of ribosomal subunits.

Chromosomes

Chromosomes- these are cytological rod-shaped structures that represent condensed chromatin and appear in the cell during mitosis or meiosis. Chromosomes and chromatin - various shapes spatial organization of the deoxyribonucleoprotein complex, corresponding different phases life cycle cells. The chemical composition of chromosomes is the same as chromatin: 1) DNA (30–45%), 2) histone proteins (30–50%), 3) non-histone proteins (4–33%).

The basis of a chromosome is one continuous double-stranded DNA molecule; The length of the DNA of one chromosome can reach several centimeters. It is clear that a molecule of such a length cannot be located in an elongated form in a cell, but undergoes folding, acquiring a certain three-dimensional structure, or conformation.

Currently accepted nucleosome model organization of eukaryotic chromatin.

During the process of converting chromatin into chromosomes, helices, supercoils, loops and superloops are formed. Therefore, the process of chromosome formation, which occurs in prophase of mitosis or prophase 1 of meiosis, is better called not spiralization, but chromosome condensation.

Chromosomes: 1 - metacentric; 2 - submetacentric; 3, 4 - acrocentric.

Chromosome structure: 5 - centromere; 6 - secondary constriction; 7 - satellite; 8 - chromatids; 9 - telomeres.

Metaphase chromosome(chromosomes are studied in metaphase of mitosis) consists of two chromatids. Any chromosome has primary constriction (centromere)(5), which divides the chromosome into arms. Some chromosomes have secondary constriction(6) and satellite(7). Satellite - a section of a short arm separated by a secondary constriction. Chromosomes that have a satellite are called satellite(3). The ends of the chromosomes are called telomeres(9). Depending on the position of the centromere, there are: a) metacentric(equal shoulder) (1), b) submetacentric(moderate unequal shoulders) (2), c) acrocentric(sharply unequal) chromosomes (3, 4).

Somatic cells contain diploid(double - 2n) set of chromosomes, sex cells - haploid(single - n). The diploid set of roundworm is 2, drosophila - 8, chimpanzee - 48, crayfish- 196. The chromosomes of the diploid set are divided into pairs; chromosomes of one pair have the same structure, size, set of genes and are called homologous.

Functions of chromosomes: 1) storage of hereditary information,

2) transfer of genetic material from the mother cell to the daughter cells.

1. Which group of organelles include lysosomes, endoplasmic reticulum and Golgi apparatus?

Single-membrane, double-membrane, non-membrane.

Lysosomes, endoplasmic reticulum and Golgi apparatus are single-membrane organelles.

2. What is the structure and functions of the endoplasmic reticulum? How does rough XPS differ from smooth XPS?

The endoplasmic reticulum (ER) is a system of channels and cavities surrounded by a membrane and penetrating the hyaloplasm of the cell. The membrane of the endoplasmic reticulum is similar in structure to the plasmalemma. The ER can occupy up to 50% of the cell volume; its channels and cavities do not break off anywhere and do not open into the hyaloplasm.

There are rough and smooth EPS. The rough ER membrane contains many ribosomes; the smooth ER membrane does not contain ribosomes. On the ribosomes of the rough ER, proteins are synthesized that are transported outside the cell, as well as membrane proteins. On the surface of the smooth ER, the synthesis of lipids, oligo- and polysaccharides occurs. In addition, Ca 2+ ions accumulate in the smooth ER - important regulators of the functions of cells and the body as a whole. The smooth ER of liver cells carries out the processes of breakdown and neutralization of toxic substances.

Rough ER is better developed in cells that synthesize large amounts of proteins (for example, in cells salivary glands and pancreas, which synthesizes digestive enzymes; in the cells of the pancreas and pituitary gland, which produce protein hormones). Smooth ER is well developed in cells that synthesize, for example, polysaccharides and lipids (adrenal and gonad cells that produce steroid hormones; liver cells that synthesize glycogen, etc.).

Substances that form on EPS membranes accumulate inside the cavities of the network and are transformed. For example, proteins acquire their characteristic secondary, tertiary or quaternary structure. Substances are then enclosed in membrane vesicles and transported to the Golgi complex.

3. How does the Golgi complex work? What functions does it perform?

The Golgi complex is a system of intracellular membrane structures: cisterns and vesicles in which substances synthesized on the ER membranes accumulate and are modified.

Substances are delivered to the Golgi complex in membrane vesicles, which are detached from the ER and attached to the cisternae of the Golgi complex. Here these substances undergo various biochemical transformations, and then are again packaged into membrane vesicles and most of them are transported to the plasmalemma. The membrane of the vesicles merges with the cytoplasmic membrane, and the contents are removed outside the cell. In the Golgi complex plant cells cell wall polysaccharides are synthesized. Another one important function Golgi complex – formation of lysosomes.

4. The largest Golgi complexes (up to 10 µm) are found in the cells of the endocrine glands. What do you think is the reason for this?

The main function of endocrine gland cells is the secretion of hormones. The synthesis of hormones occurs on the membranes of the ER, and the accumulation, transformation and excretion of these substances is carried out by the Golgi complex. Therefore, the Golgi complex is highly developed in the cells of the endocrine glands.

5. What do the structure and functions of the endoplasmic reticulum and the Golgi complex have in common? What is the difference?

Similarities:

● They are complexes of intracellular membrane structures bounded by a single membrane from the hyaloplasm (i.e. they are single-membrane organelles).

● Capable of separating membrane vesicles containing various organic substances. Together they form a single system that ensures the synthesis of substances, their modification and removal from the cell (provide “export”).

● They are best developed in those cells that specialize in the secretion of biologically active substances.

Differences:

● The main membrane components of the endoplasmic reticulum are channels and cavities, and the Golgi complex is flattened cisterns and small vesicles.

● The ER specializes in the synthesis of substances, and the Golgi complex specializes in accumulation, modification and removal from the cell.

And (or) other significant features.

6. What are lysosomes? How are they formed? What functions do they perform?

Lysosomes are small membrane vesicles that are detached from the tanks of the Golgi apparatus and contain a set of digestive enzymes that can break down various substances (proteins, carbohydrates, lipids, nucleic acids, etc.) into simpler compounds.

Food particles entering the cell from the outside are packaged in phagocytic vesicles. Lysosomes merge with these vesicles - this is how secondary lysosomes are formed, in which, under the action of enzymes, nutrients are broken down into monomers. The latter enter the hyaloplasm by diffusion, and undigested residues are removed outside the cell by exocytosis.

In addition to digesting substances that enter the cell from the outside, lysosomes take part in the breakdown internal components cells (molecules and entire organelles) that are damaged or have expired. This process is called autophagy. In addition, under the influence of lysosome enzymes, self-digestion of old cells and tissues that have lost their functional activity or damaged can occur.

7*. Suggest why the enzymes located in the lysosome do not break down its own membrane. What consequences can rupture of lysosome membranes have for a cell?

The structural components of lysosome membranes are covalently linked to a large number of oligosaccharides (unusually highly glycosylated). This prevents lysosome enzymes from interacting with membrane proteins and lipids, i.e. "digest" the membrane.

Due to rupture of lysosome membranes digestive enzymes enter the hyaloplasm, which can lead to splitting structural components cells and even to autolysis - self-digestion of the cell. However, lysosome enzymes work in an acidic environment (pH inside lysosomes is 4.5 - 5.0), but if the environment is close to neutral, which is typical for hyaloplasm (pH = 7.0 - 7.3), their activity decreases sharply. This is one of the mechanisms for protecting cells from self-digestion in the event of spontaneous rupture of lysosome membranes.

8*. It has been established that certain oligo- or polysaccharides are “attached” to the molecules of many substances that are to be removed from the cell in the Golgi complex, and different carbohydrate components are attached to different substances. In this modified form, the substances are released into the extracellular environment. What do you think this is for?

Carbohydrate components are a kind of marks or “certificates”, according to which substances arrive at the places of their functioning without being broken down along the way by the action of enzymes. Thus, using carbohydrate tags, the body distinguishes useful substances from foreign substances that need to be processed.

*Tasks marked with an asterisk require students to put forward various hypotheses. Therefore, when marking, the teacher should focus not only on the answer given here, but take into account each hypothesis, assessing the biological thinking of students, the logic of their reasoning, the originality of ideas, etc. After this, it is advisable to familiarize students with the answer given.

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 membrane organelles 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.

U multicellular organisms 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 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.
Endo and exocytotic membrane transport pathways have general patterns in the direction of movement of membrane carriers to the corresponding
targets and in the specificity of fusion and budding. The main meeting point of these paths is the AG.

Golgi apparatus (Golgi complex) - AG

The structure known today as complex or Golgi apparatus (AG) first discovered in 1898 by the Italian scientist Camillo Golgi

It was possible to study the structure of the Golgi complex in detail much later using an electron microscope.

The Golgi apparatus is usually located near the cell nucleus, near the ER (in animal cells, often near the cell center).

Golgi complex

On the left - in a cell, among other organelles.

On the right is the Golgi complex with membrane vesicles separating from it.

Functions of the Golgi apparatus:

2) Secretory - the formation of finished secretory products that are removed outside the cell by exocytosis.

3) Renewal of cell membranes, including areas of the plasmalemma, as well as replacement of defects in the plasmalemma during the secretory activity of the cell.

4) Place of formation of lysosomes.

5) Transport of substances

Lysosomes

The lysosome was discovered in 1949 by C. de Duve (Nobel Prize for 1974).

Lysosomes- single-membrane organelles. They are small bubbles (diameter from 0.2 to 0.8 microns) containing a set of hydrolytic enzymes - hydrolases. A lysosome can contain from 20 to 60 different types of hydrolytic enzymes (proteinases, nucleases, glucosidases, phosphatases, lipases, etc.) that break down various biopolymers. The breakdown of substances using enzymes is called lysis (lysis-decay).

Lysosome - membrane vesicle containing hydrolytic enzymes

Functions of lysosomes:

2. Destroy old, damaged, redundant organelles. Destruction of organelles can also occur during cell starvation.

3. Carry out autolysis (self-destruction) of cells (liquefaction of tissues in the area of inflammation, destruction of cartilage cells during the formation of bone tissue, etc.).

Autolysis - This self-destruction cells resulting from the release of contents lysosomes inside the cell. Due to this, lysosomes are jokingly called "suicide instruments". Autolysis is a normal phenomenon of ontogenesis; it can spread both to individual cells and to the entire tissue or organ, as occurs during the resorption of the tadpole’s tail during metamorphosis, i.e., when the tadpole turns into a frog

Endoplasmic reticulum, Golgi apparatus and lysosomesform a single vacuolar system of the cell, individual elements of which can transform into each other during restructuring and changing the function of membranes.

Mitochondria

Mitochondria structure:
1 - outer membrane;
2 - internal membrane; 3 - matrix; 4 - crista; 5 - multienzyme system; 6 - circular DNA.

Mitochondria limited two membranes . The outer membrane of mitochondria is smooth, the inner one forms numerous folds - cristas. Cristae increase the surface area of the inner membrane. The number of cristae in mitochondria can vary depending on the energy needs of the cell. It is on the inner membrane that numerous enzyme complexes involved in the synthesis of adenosine triphosphate (ATP) are concentrated. Here the energy of chemical bonds is converted into energy-rich (macroergic) ATP bonds . Besides, in mitochondria the breakdown of fatty acids and carbohydrates takes place, releasing energy, which is accumulated and used for the processes of growth and synthesis.The internal environment of these organelles is called matrix. It contains circular DNA and RNA, small ribosomes. Interestingly, mitochondria are semi-autonomous organelles, since they depend on the functioning of the cell, but at the same time they can maintain a certain independence. Thus, they are able to synthesize their own proteins and enzymes, as well as reproduce independently (mitochondria contain their own DNA chain, which contains up to 2% of the DNA of the cell itself).

Functions of mitochondria:

1. Conversion of the energy of chemical bonds into macroergic bonds of ATP (mitochondria are the “energy stations” of the cell).

2. Participate in the processes of cellular respiration - oxygen breakdown of organic substances.

Ribosomes

Ribosome structure:
1 - large subunit; 2 - small subunit.

Ribosomes - non-membrane organelles, approximately 20 nm in diameter. Ribosomes consist of two fragments - large and small subunits. The chemical composition of ribosomes is proteins and rRNA. rRNA molecules make up 50–63% of the mass of the ribosome and form its structural framework.

During protein biosynthesis, ribosomes can “work” individually or combine into complexes - polyribosomes (polysomes). In such complexes they are linked to each other by one mRNA molecule.

Ribosomal subunits are formed in the nucleolus. Having passed through the pores in the nuclear envelope, ribosomes enter the membranes of the endoplasmic reticulum (ER).

Function of ribosomes: assembly of a polypeptide chain (synthesis of protein molecules from amino acids).

Cytoskeleton

The cellular cytoskeleton is formed microtubules And microfilaments .

Microtubules are located in the hyaloplasm and perform the following functions:

· create an elastic, but at the same time durable frame of the cell, which allows it to maintain its shape;

· take part in the process of distribution of cell chromosomes (form a spindle);

· provide movement of organelles;

Microfilaments- filaments that are located under the plasma membrane and consist of the protein actin or myosin. They can contract, resulting in movement of the cytoplasm or protrusion of the cell membrane. In addition, these components take part in the formation of the constriction during cell division.

Cell center

The cellular center is an organelle consisting of 2 small granules - centrioles and a radiant sphere around them - the centrosphere. The centriole is a cylindrical body 0.3-0.5 µm long and about 0.15 µm in diameter. The walls of the cylinder consist of 9 parallel tubes. Centrioles are arranged in pairs at right angles to each other. The active role of the cell center is revealed during cell division. Before cell division, centrioles diverge to opposite poles, and a daughter centriole appears near each of them. They form a division spindle, which contributes to the even distribution of genetic material between daughter cells.

Centrioles are self-replicating organelles of the cytoplasm; they arise as a result of duplication of existing centrioles.

Functions:

1. Ensuring uniform divergence of chromosomes to the poles of the cell during mitosis or meiosis.

2. Center for cytoskeletal organization.

Organoids of movement

Not present in all cells

Organelles of movement include cilia and flagella. These are miniature growths in the form of hairs. The flagellum contains 20 microtubules. Its base is located in the cytoplasm and is called the basal body. The length of the flagellum is 100 µm or more. Flagella, which are only 10-20 microns, are called eyelashes . When microtubules slide, cilia and flagella are able to vibrate, causing the cell itself to move. The cytoplasm may contain contractile fibrils called myofibrils. Myofibrils, as a rule, are located in myocytes - muscle tissue cells, as well as in heart cells. They consist of smaller fibers (protofibrils).

In animals and humans cilia they line the airways and help get rid of small particulate matter, such as dust. In addition, there are also pseudopods that provide amoeboid movement and are elements of many unicellular and animal cells (for example, leukocytes).

Functions:

Specific

Core. Chromosomes