Laboratory-practical lesson No. 9

Topic: "Apparatus (complex) Golgi"

Purpose of the lesson : to reveal the morpho-functional features of the Golgi complex.

Issues for discussion

1 . Fine structure of the Golgi apparatus.

Demonstration preparations

Equipment

1. Photos, diagrams, drawings fromAtlas of Cell Biology, J.-K.Roland, A. Seloshi, D. Seloshi, per.V.P. Bely, ed. Yu.S. Chentsov. ─ M.: Mir. 1978. - 119 p.

Theoretical justification to prepare for class

The Golgi apparatus (complex) is a membrane structure of a eukaryotic cell, an organelle mainly intended for the excretion of substances synthesized in the endoplasmic reticulum. The Golgi apparatus was named after the Italian scientist Camillo Golgi, who first discovered it in 1897 (Fabene P.F., Bentivoglio M., 1998).

Rice. 1. Scheme of the Golgi Apparatus (A). The structure of the Golgi apparatus (B)

Note: Golgi apparatus ─ cavities (cistern) surrounded by membranes and a system of vesicles associated with them. Functions ─ accumulation of organic substances; "packaging" of organic substances; excretion of organic substances; the formation of lysosomes.

Apparatus(complex) Golgi is a stack of disk-shaped membranous sacs (cistern), somewhat expanded closer to the edges, and the system of Golgi vesicles associated with them. A number of individual stacks are found in plant cells ( dictyosomes), animal cells often contain one large or several stacks connected by tubes.

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

1. Cis-section (closest to the nucleus).

2. Medial department.

3. Trans-section (the most distant from the nucleus).

These departments differ from each other by a set of enzymes. In the cis section, the first cistern is called the "cistern of salvation", since with its help the receptors coming from the intermediate endoplasmic reticulum return back. Enzyme of the cis-section: phosphoglycosidase (attaches phosphate to the carbohydrate ─ mannose).

In the medial section there are 2 enzymes: mannasidase (cleaves off mannase) and N-acetylglucosamine transferase (attaches certain carbohydrates ─ glycosamines).

In the trans section, enzymes: peptidase (carries out proteolysis) and transferase (carries out the transfer of chemical groups).

Fine structure of the Golgi apparatus (AG). An electron microscope shows that the Golgi apparatus is represented by membrane structures assembled together in a small zone (Fig. 1, 2); in the form of a stack, flat membrane bags (tanks) are located, the number of such bags in a stack usually does not exceed 5-10. Between which are thin layers of hyaloplasm. Each individual tank is about 1 µm in diameter and variable in thickness; in the center of the membrane they can be brought together (25 nm), and on the periphery they can have extensions ─ ampoules, the width of which is not constant.

Rice. 2. Scheme of the structure of the dictyosome(according to Chentsov Yu.S., 2010)

Note : P─ proximal (cis-) part; D─ distal (trans-) part; AT─ vacuoles; C─ flat membrane tanks; BUT─ ampullary expansions of cisterns.

In some unicellular organisms, their number can reach 20 pieces. In addition to densely spaced 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 on the edges of flat tanks. It is customary to distinguish between a proximal or emerging cis-section in the dictyosome zone, and a distal or mature trans-section (Fig. 15.5). Between them is the middle or intermediate section of the AG. During cell division reticular forms of AG disintegrate into dictyosomes who are passive

and randomly distributed among the daughter cells. As cells grow, the total number of dictyosomes increases.

Rice. 3. Types of Golgi apparatus(according to Chentsov Yu.S., 2010)

Note : a ─ reticulate in cells of the intestinal epithelium;b─ diffuse in spinal ganglion cells;I─ core;2 ─ AG;3 ─ nucleolus.

AG is usually polarized in secreting cells: its proximal part faces the cytoplasm and nucleus, and its distal ─ to the surface of the cell. In the proximal area, a zone of small smooth vesicles and short membranous cisterns adjoins the stacks of contiguous cisterns.

Rice. 4. Golgi apparatus (AG) in electronic mikroscope(according to Chentsov Yu.S., 2010)

Rice. 5. Schematic representation of the components of the Golgi apparatus(according to Chentsov Yu.S., 2010)

Note : 1 ─ EPR-AG (ERGIC) ─ intermediate zone;2 ─ cis-zone, proximal area; 3─ medial─ middle section; 4─ trans-distal area; 5─ AG trans-network.

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

In the distal or trans-section of dictyosomes, the last membranous squamous cistern is adjacent to a section consisting of tubular elements and a mass of small vacuoles, often with fibrillar pubescence on the surface from the side of the cytoplasm - these are pubescent or bordered vesicles of the same type as bordered vesicles in pinocytosis ( from other Greek πίνω ─ drink, absorb and κύτος ─ receptacle, cell ─ capture by the cell surface of the liquid with the substances contained in it; the process of absorption and intracellular destruction of macromolecules).

This is the so-called trans-Golgi network (TGN), where secreted products are separated and sorted. Even more distal is a group of larger vacuoles ─ this is already the product of the fusion of small vacuoles and the formation of secretory vacuoles.

When studying thick sections of cells in a megavolt electron microscope, it was found that individual dictosomes in cells can be connected to each other by a system of vacuoles and cisterns. So a loose three-dimensional network is formed, which is revealed in a light microscope. In the case of a diffuse form of AH, each of its individual sections is represented by a dictyosome. In animal cells, centrioles are often associated with the membrane zone of the Golgi apparatus; between the bundles of microtubules that extend radially from them, there are groups of stacks of membranes and vacuoles that concentrically surround the cell center. This relationship likely reflects the involvement of microtubules in vacuole movement.

Functions golgi apparatus.Along with proteins, membrane lipids are transported in the Golgi apparatus.

1. Separation of proteins into 3 streams:

● CIS department (closest to the nucleus); lysosomal ─ glycosylated proteins (with mannose) enter the cis-section of the Golgi complex, some of them are phosphorylated, a marker of lysosomal enzymes ─ mannose-6-phosphate is formed. In the future, these phosphorylated proteins will not undergo modification, but will enter the lysosomes.

● Medial department; constitutive exocytosis (constitutive secretion). This stream includes proteins and lipids, which become components of the surface apparatus of the cell, including the glycocalyx, or they can be part of the extracellular matrix.

● Trans department (farthest from the core); induced secretion ─ proteins that function outside the cell, the surface apparatus of the cell, in the internal environment of the body get here. characteristic of secretory cells.

2. Formation of mucous secretions (secretory function of the Golgi apparatus) ─ glycosaminoglycans(mucopolysaccharides).

● Membrane elements AG participate in the segregation and accumulation of products synthesized in the ER, participate in their chemical rearrangements, maturation (restructuring of the oligosaccharide components of glycoproteins in the composition of water-soluble secrets or in the composition of membranes) (Fig. 6).

● In AG tanks there is a synthesis of polysaccharides, their relationship with proteins, leading to the formation of mucoproteins.

●Most importantly, with the help of the elements of the Golgi apparatus, the process of removing ready-made secrets outside the cell takes place. In addition, AG is a source of cellular lysosomes.

● The involvement of AG in the processes of excretion of secretory products has been very well studied on the example of exocrine cells of the pancreas. 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, carbohydrases, nucleases.

During secretion, the contents of these zymogen granules are ejected 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, we studied the sequence of incorporation of radioactive amino acids into different parts of the cell (Fig. 7).

Rice. Fig. 6. Scheme of the relationship of the EPR, the Golgi apparatus with the formation and release of the zymogen from the acinar cells of the pancreas (according to Chentsov Yu.S., 2010)

Note : 1 ─ transition zone between EPR and AG; 2─ zone of maturation of secretory granules;3 ─ zymogen granules separated from AG; 4─ their release (exocytosis) outside the cell.

Rice. 7. Detection sequence}