The endoplasmic reticulum, or endoplasmic reticulum, is a system of tubes and cavities penetrating the cytoplasm of a cell. EPS is formed by a membrane that has the same structure as the plasma membrane. The tubules and cavities of the EPS can occupy up to 50% of the cell volume and do not break anywhere and do not open into the cytoplasm. There are smooth and rough (granular) EPS. The rough ER contains many ribosomes. This is where most proteins are synthesized. On the surface of the smooth EPS, carbohydrates and lipids are synthesized.
Functions of the granular endoplasmic reticulum:
- synthesis of proteins intended for removal from the cell ("for export");
- separation (segregation) of the synthesized product from the hyaloplasm;
- condensation and modification of the synthesized protein;
- transport of the synthesized products into the cisterns of the lamellar complex or directly from the cell;
- synthesis of lipid membranes.
The smooth endoplasmic reticulum is represented by cisterns, wider channels, and individual vesicles, on the outer surface of which there are no ribosomes.
Functions of the smooth endoplasmic reticulum:
- participation in the synthesis of glycogen;
- synthesis of lipids;
- Detoxification function - neutralization of toxic substances by combining them with other substances.
Golgi complex (apparatus).
The system of intracellular tanks, in which substances synthesized by the cell accumulate, is called the Golgi complex (apparatus). Here, these substances undergo further biochemical transformations, are packed into membrane vesicles and transferred to those places in the cytoplasm where they are needed, or they are transported to the cell membrane and leave the cell (Fig. 32). The Golgi complex is built of membranes and is located next to the EPS, but does not communicate with its channels. Therefore, all substances synthesized on the ER membranes are transferred to the Golgi complex inside the membrane vesicles that bud from the ER and then merge with the Golgi complex. Another important function of the Golgi complex is the assembly of cell membranes. The substances that make up the membranes (proteins, lipids) enter the Golgi complex from the ER, in the cavities of the Golgi complex, sections of the membranes are collected, from which special membrane vesicles are made. They move through the cytoplasm to those places in the cell where the membrane needs to be completed.
Functions of the Golgi apparatus:
- Sorting, accumulation and excretion of secretory products;
- accumulation of lipid molecules and the formation of lipoproteins;
- The formation of lysosomes
- synthesis of polysaccharides for the formation of glycoproteins, waxes, gums, mucus, substances of the matrix of plant cell walls;
- Formation of a cell plate after nuclear fission in plant cells;
- Formation of contractile vacuoles in protozoa.
The cell is a whole system
A living cell is a unique, perfect, smallest unit of an organism; it is arranged in such a way as to use oxygen and nutrients as efficiently as possible, while performing its functions. The organelles vital for the cell are the nucleus, ribosomes, mitochondria, endoplasmic reticulum, Golgi apparatus. Let's talk about the latter in more detail.
What it is
This membrane organelle is a complex of structures that remove the substances synthesized in it from the cell. Most often, it is located near the outer cell membrane.
Golgi apparatus: structure
It consists of "sacs" formed by membranes called cisterns. The latter have an elongated shape, slightly flattened in the middle and expanded along the edges. Also in the complex there are round Golgi vesicles - small membrane structures. Cisterns are “stacked” in stacks called dictyosomes. The Golgi apparatus contains various types of "sacs", the whole complex is divided into some parts according to the degree of remoteness from the nucleus. There are three of them: the cis-section (closer to the nucleus), the median, and the trans-section - the furthest from the nucleus. They are characterized by a different composition of enzymes, and hence the work performed. There is one feature in the structure of dictyosomes: they are polar, that is, the section closest to the nucleus only receives vesicles coming from the endoplasmic reticulum. The part of the "stack" facing the cell membrane only forms and releases them.
Golgi apparatus: functions
The main tasks performed are the sorting of proteins, lipids, mucous secretions and their excretion. Also, non-protein substances secreted by the cell, carbohydrate components of the outer membrane, pass through it. At the same time, the Golgi apparatus is not at all an indifferent intermediary that simply “transfers” substances, it undergoes processes of activation and modification (“maturation”):
- Sorting of substances, transport of proteins. The distribution of protein substances occurs in three streams: for the membrane of the cell itself, export, lysosomal enzymes. In the first stream, in addition to proteins, fats are also included. Interesting fact that any export substances are carried inside the bubbles. But the proteins intended for the cell membrane are integrated into the membrane of the transport vesicle and move in this way.
- Isolation of all products produced in the cell. The Golgi apparatus "packs" all products, both protein and other nature, into secretory vesicles. All substances are released outside through the complex interaction of the latter with the cell membrane.
- Synthesis of polysaccharides (glycosaminoglycans and components of the cell wall glycocalyx).
- Sulfation, glycosylation of fats and proteins, partial proteolysis of the latter (necessary to transfer them from an inactive form to an active one) - these are all the processes of “maturation” of proteins necessary for their future full-fledged work.
Finally
Having considered how the Golgi complex is arranged and works, we are convinced that it is the most important and integral part of any cell (especially secretory ones). A cell that does not produce substances for export also cannot do without this organelle, since the “completeness” of the cell membrane and other important internal life processes depend on it.
18. Golgi complex, its structure and functions. Lysosomes. Their structure and functions. types of lysosomes.
Golgi complex represents a stack of disk-shaped membrane sacs (cistern), somewhat expanded closer to the edges, and the system of Golgi vesicles associated with them. In plant cells, a number of separate stacks (dictyosomes) are found, in animal cells there is often one large or several stacks connected by tubes.
1. Accumulates and removes organic substances synthesized in the endoplasmic reticulum
2. Forms lysosomes
3. Formation of carbohydrate components of the glycocalyx - mainly glycolipids.
Lysosomes are an integral part of the composition of the cell. They are a type of vesicle. These cellular helpers, being part of the vacuum, are sheathed in membranes and filled with hydrolytic enzymes. The importance of the existence of lysosomes inside the cell is provided by the secretory function, which is necessary in the process of phagocytosis and autophagocytosis.
Perform digestive function- digest food particles and remove dead organelles.
Primary lysosomes- These are small membrane vesicles, which have a diameter of about one hundred nm, filled with a homogeneous fine content, which is a set of hydrolytic enzymes. There are about forty enzymes in lysosomes.
Secondary lysosomes are formed by the fusion of primary lysosomes with endocytic or pinocytic vacuoles. In other words, secondary lysosomes are intracellular digestive vacuoles, the enzymes of which are supplied by primary lysosomes, and the material for digestion is supplied by endocytic (pinocytic) vacuoles.
19. Eps, its varieties, role in the processes of synthesis of substances.
Endoplasmic reticulum in different cells it can be presented in the form of flattened cisterns, tubules or individual vesicles. The wall of these formations consists of a bilipid membrane and some proteins included in it and delimits the internal environment of the endoplasmic reticulum from the hyaloplasm.
There are two types of endoplasmic reticulum:
granular (granular or rough);
non-grained or smooth.
Ribosomes are attached to the outer surface of the membranes of the granular endoplasmic reticulum. In the cytoplasm, there can be both types of the endoplasmic reticulum, but usually one form predominates, which determines the functional specificity of the cell. It should be remembered that these two varieties are not independent forms of the endoplasmic reticulum, since it is possible to trace the transition from a granular endoplasmic reticulum to a smooth one and vice versa.
Functions of the granular endoplasmic reticulum:
synthesis of proteins intended for removal from the cell ("for export");
separation (segregation) of the synthesized product from the hyaloplasm;
condensation and modification of the synthesized protein;
transport of synthesized products into cisterns of the lamellar complex or directly from the cell;
synthesis of lipid membranes.
The smooth endoplasmic reticulum is represented by cisterns, wider channels, and individual vesicles, on the outer surface of which there are no ribosomes.
Functions of the smooth endoplasmic reticulum:
participation in the synthesis of glycogen;
lipid synthesis;
detoxification function - neutralization of toxic substances by combining them with other substances.
The lamellar Golgi complex (mesh apparatus) is represented by an accumulation of flattened cisterns and small vesicles bounded by a bilipid membrane. The lamellar complex is subdivided into subunits - dictyosomes. Each dictyosome is a stack of flattened cisterns, along the periphery of which small vesicles are localized. At the same time, in each flattened tank, the peripheral part is somewhat expanded, and the central one is narrowed.
Golgi complex is a membrane structure inherent in any eukaryotic cell.
The Golgi apparatus is represented flattened tanks(or bags) collected in a pile. Each tank is slightly curved and has convex and concave surfaces. The average diameter of the tanks is about 1 micron. In the center of the tank, its membranes are brought together, and on the periphery they often form extensions, or ampoules, from which they lace up. bubbles. Packages of flat tanks with an average of about 5-10 form dictyosome. In addition to cisterns, the Golgi complex contains transport and secretory vesicles. In the dictyosome, two surfaces are distinguished in accordance with the direction of curvature of the curved surfaces of the cisterns. The convex surface is called immature, or cis-surface. It faces the nucleus or tubules of the granular endoplasmic reticulum and is connected with the latter by vesicles that detach from the granular reticulum and bring protein molecules into the dictyosome for maturation and formation into the membrane. The opposite transsurface of the dictyosome is concave. It faces the plasmolemma and is called mature because secretory vesicles are laced from its membranes, containing secretion products ready for removal from the cell.
The Golgi complex is involved in:
- in the accumulation of products synthesized in the endoplasmic reticulum,
- in their chemical restructuring and maturation.
AT cisterns of the Golgi complex there is a synthesis of polysaccharides, their complexation with protein molecules.
One of main functions Golgi complex - formation of finished secretory products, which are removed from the cell by exocytosis. The most important functions of the Golgi complex for the cell are also update cell membranes , including sections of the plasmolemma, as well as the replacement of defects in the plasmolemma during the secretory activity of the cell.
The Golgi complex is considered source of formation of primary lysosomes, although their enzymes are also synthesized in the granular network. Lysosomes are intracellularly formed secretory vacuoles filled with hydrolytic enzymes necessary for the processes of phago- and autophagocytosis. At the light-optical level, lysosomes can be identified and judged on the degree of their development in the cell by the activity of the histochemical reaction to acid phosphatase, the key lysosomal enzyme. Under electron microscopy, lysosomes are defined as vesicles, limited from the hyaloplasm by a membrane. Conventionally, there are 4 main types of lysosomes:
- primary,
- secondary lysosomes,
- autophagosomes,
- residual bodies.
Primary lysosomes- these are small membrane vesicles (their average diameter is about 100 nm), filled with a homogeneous fine content, which is a set of hydrolytic enzymes. About 40 enzymes (proteases, nucleases, glycosidases, phosphorylases, sulfatases) have been identified in lysosomes, the optimal mode of action of which is designed for an acidic environment (pH 5). Lysosomal membranes contain special carrier proteins for transport from the lysosome to the hyaloplasm of hydrolytic cleavage products - amino acids, sugars and nucleotides. The lysosome membrane is resistant to hydrolytic enzymes.
Secondary lysosomes are formed by the fusion of primary lysosomes with endocytic or pinocytic vacuoles. In other words, secondary lysosomes are intracellular digestive vacuoles, the enzymes of which are supplied by primary lysosomes, and the material for digestion is supplied by endocytic (pinocytic) vacuoles. The structure of secondary lysosomes is very diverse and changes in the process of hydrolytic cleavage of the contents. Lysosome enzymes break down those that enter the cell biological substances, resulting in the formation of monomers that are transported through the lysosome membrane to the hyaloplasm, where they are utilized or included in various synthetic and metabolic reactions.
If the cell's own structures (senescent organelles, inclusions, etc.) undergo interaction with primary lysosomes and hydrolytic cleavage by their enzymes, a autophagosome. Autophagocytosis is a natural process in the life of a cell and plays an important role in the renewal of its structures during intracellular regeneration.
Residual bodies this is one of the final stages of the existence of phago- and autolysosomes and is found during incomplete phago- or autophagocytosis and subsequently isolated from the cell by exocytosis. They have a compacted content, often there is a secondary structuring of undigested compounds (for example, lipids form complex layered formations).
The Golgi apparatus consists of cisterns (disc-shaped membranous sacs), which are slightly expanded closer to the edges. The structure of the Golgi complex can be divided into 3 departments:
1. Cis-cistern or cis-compartment. Located closer to the nucleus and endoplasmic reticulum;
2. Connecting tanks. Middle section of the Golgi apparatus;
3. Trans cisterns or trans compartment. The section furthest from the nucleus and, accordingly, the closest to the cell membrane.
You can also see what the Golgi complex looks like in a cell using the example of the structure of an animal cell or the structure of a plant cell.
Functions of the Golgi complex (apparatus)
The main functions of the Golgi apparatus include:
1. Removal of substances synthesized in the endoplasmic reticulum;
2. Modification of newly synthesized protein molecules;
3. Separates proteins into 3 streams;
4. Formation of mucous secretions;
5. In the plant cell is responsible for the synthesis of polysaccharides, which then go to the formation of the plant cell wall;
6. Partial proteolysis of proteins;
7. Produces the formation of lysosomes, cell membrane;
8. Sulfation of carbohydrate and protein components of glycoproteins and glycolipids;
9. Formation of carbohydrate components of the glycocalyx - mainly glycolipids.