The ER is a system of flattened membrane sacs, tubules, cisterns, and vesicles. The entire network is integrated into a single whole with the outer membrane of the nuclear envelope and the outer cell membrane. There are two types of EPR: granular (rough) and agranular (smooth).

The membranes of the granular endoplasmic reticulum on the hyaloplasmic side are covered with ribosomes.

Functions of granular EPR:

Ensuring the biosynthesis of proteins intended for removal from the cell;

Segregation (separation) of newly synthesized protein molecules from the hyaloplasm;

Biosynthesis of membrane proteins;

Initial post-translational changes in proteins.

The smooth ER is also represented by membranes that form small vacuoles and tubes, tubules, which can branch and merge with each other. Unlike granular ER, smooth ER has no ribosomes on its membranes. Smooth and rough EPR are interconnected and transform into each other.

The functions of a smooth EPR are:

Synthesis and metabolism of lipids (including membrane lipids);

Glycogen metabolism. Glycogen is deposited in the smooth ER of liver cells and muscle fibers;

Synthesis of cholesterol and steroid hormones;

Degradation and detoxification of various harmful substances (carcinogens, toxic substances, hormonal drugs and other drugs, alcohol);

Deposition of Ca 2+ ions (sarcoplasmic reticulum).

Golgi apparatus (Golgi complex, lamellar complex).

The Golgi complex is a collection of membrane structures in the form of a stack (dictyosome). Between the stacks there are thin layers of hyaloplasm. In secreting cells, the Golgi apparatus is usually polarized: on one side, membrane sacs are continuously formed (cis-section), and on the other, vacuoles are separated (trans-section). The cisternae of the Golgi apparatus are connected to the ER tubules. In some cells, the Golgi apparatus takes the form of complex networks.

Functions of the Golgi apparatus:

Synthesis of polysaccharides, their interaction with proteins, leading to the formation of glycoproteins (for example, glycocalyx);

Modification of proteins in the Golgi apparatus. Proteins “mature” as they move through the cisternae of the Golgi apparatus, i.e. are subject to modifications: some of their amino acids are phosphorylated, acetylated, etc. The oligosaccharide chains of proteins are also subject to modification. In this case, a special complex of oligosaccharides appears;

Removal of ready-made secretions outside the cell. The exported protein, synthesized on ribosomes and modified into AG, is packaged into vacuoles in the trans region of the dictyosome. Such vacuoles move to the cell surface, come into contact with the plasma membrane and merge with it (exocytosis). Thus, the contents of the vacuoles appear outside the cell;

Sorting of proteins in the Golgi apparatus.

Lysosomes.

They are bubbles bounded by a single membrane with heterogeneous contents inside. All lysosomes contain hydrolase enzymes (about 40 types are known), which allows them to participate in intracellular digestion processes. Based on morphology, primary, secondary lysosomes, autophagosomes and telolysosomes (residual bodies) can be distinguished.

Primary lysosomes are small membrane vesicles 50-100 nm containing a set of hydrolases. These are inactive structures that have not yet entered into the processes of cleavage of substrates.

Secondary lysosomes are the product of the fusion of primary lysosomes with phagocytic or pinocytotic vacuoles. In this case, hydrolases of the primary vacuole gain access to substrates, which they begin to break down.

Autophagosomes (autolysosomes) are secondary lysosomes that perform the function of destroying changed or expired cellular components.

Telolysosomes (residual bodies) are secondary lysosomes containing incompletely digested metabolic products or pigment substances.

Organelles of general importance. Endoplasmic reticulum.

Organelles - structures constantly present in the cytoplasm, specialized to perform certain functions in the cell. They are divided into organelles of general and special significance.

The endoplasmic reticulum, or endoplasmic reticulum, is a system of flat membrane cisterns and membrane tubes. Membrane tanks and tubes are interconnected and form a membrane structure with common contents. This allows you to isolate certain areas of the cytoplasm from the main nialoplasm and implement some specific cellular functions in them. As a result, functional differentiation of different zones of the cytoplasm occurs. The structure of EPS membranes corresponds to the liquid mosaic model. Morphologically, two types of EPS are distinguished: smooth (agranular) and rough (granular). Smooth ER is represented by a system of membrane tubes. Rough EPS is a membrane tank system. On the outside of the rough EPS membranes there are ribosomes. Both types of EPS are structurally dependent - membranes of one type of EPS can transform into membranes of another type.

Functions of the endoplasmic reticulum:

1.Granular EPS is involved in protein synthesis; complex protein molecules are formed in the channels.

2. Smooth EPS is involved in the synthesis of lipids and carbohydrates.

3.Transport of organic substances into the cell (through EPS channels).

4. Divides the cell into sections, in which different chemical reactions and physiological processes can occur simultaneously.

Smooth XPS is multifunctional. Its membrane contains enzyme proteins that catalyze the reactions of membrane lipid synthesis. Some non-membrane lipids (steroid hormones) are also synthesized in the smooth ER. The membrane of this type of EPS includes Ca2+ transporters. They transport calcium along a concentration gradient (passive transport). During passive transport, ATP is synthesized. With their help, the concentration of Ca2+ in the hyaloplasm is regulated in the smooth ER. This parameter is important for regulating the functioning of microtubules and microfibrils. In muscle cells, smooth ER regulates muscle contraction. The EPS detoxifies many substances harmful to the cell (medicines). Smooth ER can form membrane vesicles, or microbodies. Such vesicles carry out specific oxidative reactions in isolation from the EPS.

Main function rough XPS is protein synthesis. This is determined by the presence of ribosomes on the membranes. The membrane of the rough ER contains special proteins ribophorins. Ribosomes interact with ribophorins and are fixed to the membrane in a certain orientation. All proteins synthesized in the EPS have a terminal signal fragment. On the ribosomes of the rough ER, three types of proteins are synthesized:

1.Membrane proteins. All proteins of the plasma membrane, the membranes of the EPS itself, and most proteins of other organelles are products of EPS ribosomes.

2. Secretory proteins. These proteins enter the ER cavity and are then removed from the cell by exocytosis.

3.Intraorganoid proteins. These proteins are localized and function in the cavities of membrane organelles: the ER itself, the Golgi complex, lysosomes, and mitochondria. EPS is involved in the formation of biomembranes.

Post-translational modification of proteins occurs in the rough ER cisterns.

EPS is a universal organelle of eukaryotic cells. Violation of the structure and function of the ER leads to serious consequences. The ER is the site of formation of membrane vesicles with specialized functions (peroxisomes).

A little history

A cell is considered the smallest structural unit of any organism, but it also consists of something. One of its components is the endoplasmic reticulum. Moreover, EPS is an essential component of any cell in principle (except for some viruses and bacteria). It was discovered by the American scientist K. Porter back in 1945. It was he who noticed the systems of tubules and vacuoles that seemed to have accumulated around the nucleus. Porter also noticed that the sizes of the EPS in the cells of different creatures and even organs and tissues of the same organism are not similar to each other. He came to the conclusion that this is due to the functions of a particular cell, the degree of its development, as well as the stage of differentiation. For example, in humans, EPS is very well developed in the cells of the intestines, mucous membranes and adrenal glands.

Concept

EPS is a system of tubules, tubes, vesicles and membranes that are located in the cytoplasm of the cell.

Endoplasmic reticulum: structure and functions

Brief information about the other most important components of the cell

Cytoplasm: structure and functions

Cell membrane: structure and functions

Core: structure and functions

Ribosomes

They are organelles that provide basic protein synthesis. They can be found both in the free space of the cell cytoplasm and in complex with other organelles (endoplasmic reticulum, for example). If ribosomes are located on the membranes of rough ER (being on the outer walls of the membranes, ribosomes create roughness) , the efficiency of protein synthesis increases several times. This has been proven by numerous scientific experiments.

Golgi complex

An organoid consisting of certain cavities that constantly secrete vesicles of various sizes. The accumulated substances are also used for the needs of the cell and the body. The Golgi complex and the endoplasmic reticulum are often located nearby.

Lysosomes

Organelles surrounded by a special membrane and performing the digestive function of the cell are called lysosomes.

Mitochondria

Organelles surrounded by several membranes and performing an energy function, that is, ensuring the synthesis of ATP molecules and distributing the resulting energy throughout the cell.

Plastids. Types of plastids

Chloroplasts (photosynthetic function);

Chromoplasts (accumulation and preservation of carotenoids);

Leukoplasts (accumulation and storage of starch).

Organelles designed for locomotion

They also make some movements (flagella, cilia, long processes, etc.).

Cellular center: structure and functions

The endoplasmic reticulum in different cells 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-grainy or smooth.

The outer surface of the membranes of the granular endoplasmic reticulum contains attached ribosomes. There may be both types of endoplasmic reticulum in the cytoplasm, but usually one form predominates, which determines the functional specificity of the cell. It should be remembered that the two named varieties are not independent forms of the endoplasmic reticulum, since one can trace the transition of the granular endoplasmic reticulum to the 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 synthesized protein;

transport of synthesized products into the tanks of the lamellar complex or directly from the cell;

synthesis of bilipid 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 smooth endoplasmic reticulum:

participation in glycogen synthesis;

lipid synthesis;

detoxification function - neutralization of toxic substances by combining them with other substances.

The lamellar Golgi complex (reticular apparatus) is represented by a cluster of flattened cisterns and small vesicles bounded by a bilipid membrane. The lamellar complex is divided into subunits - dictyosomes. Each dictyosome is a stack of flattened cisternae, along the periphery of which small vesicles are localized. At the same time, in each flattened cistern, the peripheral part is somewhat expanded, and the central part is narrowed.

There are two poles in the dictyosome:

cis-pole - directed with its base towards the nucleus;

trans-pole - directed towards the cytolemma.

It has been established that transport vacuoles approach the cis-pole, carrying products synthesized in the granular endoplasmic reticulum into the lamellar complex. Vesicles are released from the trans-pole, carrying the secretion to the plasmalemma for its removal from the cell. However, some of the small vesicles filled with enzyme proteins remain in the cytoplasm and are called lysosomes.

Functions of the plate complex:

transport - removes products synthesized in it from the cell;

condensation and modification of substances synthesized in the granular endoplasmic reticulum;

formation of lysosomes (together with granular endoplasmic reticulum);

participation in carbohydrate metabolism;

synthesis of molecules that form the glycocalyx of the cytolemma;

synthesis, accumulation and excretion of mucin (mucus);

modification of membranes synthesized in the endoplasmic reticulum and their transformation into plasmalemma membranes.

Among the numerous functions of the lamellar complex, the transport function is put in first place. That is why it is often called the transport apparatus of the cell.

Lysosomes are the smallest organelles of the cytoplasm (0.2-0.4 µm) and therefore open (de Duve, 1949) only using an electron microscope. They are bodies bounded by a lipid membrane and containing an electron-dense matrix consisting of a set of hydrolytic enzyme proteins (50 hydrolases) capable of breaking down any polymer compounds (proteins, lipids, carbohydrates and their complexes) into monomeric fragments. The marker enzyme of lysosomes is acid phosphatase.

The function of lysosomes is to ensure intracellular digestion, that is, the breakdown of both exogenous and endogenous substances.

Classification of lysosomes:

primary lysosomes are electron-dense bodies;

secondary lysosomes - phagolysosomes, including autophagolysosomes;

tertiary lysosomes or residual bodies.

True lysosomes are small electron-dense bodies formed in the lamellar complex.

The digestive function of lysosomes begins only after the fusion of a lysosome with a phagosome, that is, a phagocytosed substance surrounded by a bilipid membrane. In this case, a single vesicle is formed - a phagolysosome, in which the phagocytosed material and lysosome enzymes are mixed. After this, the splitting (hydrolysis) of the biopolymer compounds of the phagocytosed material into monomeric molecules (amino acids, monosaccharides, etc.) begins. These molecules freely penetrate through the phagolysosome membrane into the hyaloplasm and are then utilized by the cell, that is, they are used either for the generation of energy or for the construction of biopolymer structures. But phagocytosed substances are not always completely broken down.

The further fate of the remaining substances may be different. Some of them can be removed from the cell by exocytosis, a mechanism reverse to phagocytosis. Some substances (primarily of a lipid nature) are not broken down by lysosomal hydrolases, but accumulate and become compacted in the phagolysosome. Such formations are called tertiary lysosomes or residual bodies.

In the process of phagocytosis and exocytosis, the regulation of membranes in the cell is carried out:

during the process of phagocytosis, part of the plasma membrane is detached and forms the phagosome shell;

during the process of exocytosis, this membrane is again integrated into the plasmalemma.

It has been established that some cells completely renew the plasmalemma within an hour.

In addition to the considered mechanism of intracellular breakdown of phagocytosed exogenous substances, endogenous biopolymers—damaged or obsolete own structural elements of the cytoplasm—are destroyed in the same way. Initially, such organelles or entire sections of the cytoplasm are surrounded by a bilipid membrane and an autophagolysosome vacuole is formed, in which hydrolytic cleavage of biopolymer substances occurs, as in the phagolysosome.

It should be noted that all cells contain lysosomes in the cytoplasm, but in varying quantities. There are specialized cells (macrophages), the cytoplasm of which contains a lot of primary and secondary lysosomes. Such cells perform protective functions in tissues and are called cleanser cells, since they are specialized to absorb a large number of exogenous particles (bacteria, viruses), as well as decayed tissues of their own.

Peroxisomes are cytoplasmic microbodies (0.1-1.5 µm), similar in structure to lysosomes, but differ from them in that their matrix contains crystal-like structures, and among the enzyme proteins there is catalase, which destroys hydrogen peroxide formed during oxidation amino acids.

Endoplasmic reticulum (ER) , or endoplasmic reticulum (ER), is a system consisting of membrane cisterns, channels and vesicles. About half of all cell membranes are located in the ER.

Morphofunctionally, the EPS is differentiated into 3 sections: rough (granular), smooth (agranular) and intermediate. The granular ER contains ribosomes (PC), while the smooth and intermediate ER lack them. The granular ER is mainly represented by cisterns, while the smooth and intermediate ER is mainly represented by channels. The membranes of tanks, channels and bubbles can pass into each other. ER contains a semi-liquid matrix characterized by a special chemical composition.

ER functions:

• compartmentalization;
• synthetic;
• transport;
• detoxification;
• regulation of calcium ion concentration.

Compartmentalization function associated with the division of cells into compartments (compartments) using ER membranes. Such division makes it possible to isolate part of the contents of the cytoplasm from the hyaloplasm and allows the cell to isolate and localize certain processes, as well as make them occur more efficiently and in a directed manner.

Synthetic function. Almost all lipids are synthesized on the smooth ER, with the exception of two mitochondrial lipids, the synthesis of which occurs in the mitochondria themselves. Cholesterol is synthesized on the membranes of the smooth ER (in humans, up to 1 g per day, mainly in the liver; with liver damage, the amount of cholesterol in the blood drops, the shape and function of red blood cells change, and anemia develops).
Protein synthesis occurs on the rough ER:

• internal phase of the ER, Golgi complex, lysosomes, mitochondria;
• secretory proteins, for example hormones, immunoglobulins;
• membrane proteins.

Protein synthesis begins on free ribosomes in the cytosol. After chemical transformations, proteins are packaged into membrane vesicles, which are detached from the ER and transported to other areas of the cell, for example, to the Golgi complex.
Proteins synthesized in the ER can be divided into two streams:

• internal ones, which remain in the ER;
• external ones that do not remain in the ER.

Internal proteins, in turn, can also be divided into two streams:

• residents who do not leave the Republic of Estonia;
• transit, leaving the Republic of Estonia.

Happens in the ER detoxification of harmful substances that have entered the cell or formed in the cell itself. Most harmful substances are
hydrophobic substances, which therefore cannot be excreted from the body in urine. The ER membranes contain a protein called cytochrome P450, which converts hydrophobic substances into hydrophilic ones, and after that they are removed from the body in the urine.