Cell inclusions: structure and functions, medical and biological significance. Cytoplasm and its structural components

Eukaryotes include the kingdoms of plants, animals, and fungi.

The main features of eukaryotes.

The cell is divided into cytoplasm and nucleus.
Most of the DNA is concentrated in the nucleus. It is nuclear DNA that is responsible for most of the life processes of the cell and for the transmission of heredity to daughter cells.
Nuclear DNA is dissected into strands that are not closed into rings.
DNA strands are linearly elongated inside the chromosomes, clearly visible during mitosis. The set of chromosomes in the nuclei of somatic cells is diploid.
The system of external and internal membranes is developed. Internal divide the cell into separate compartments - compartments. They take part in the formation of cell organelles.
There are many organelles. Some organelles are surrounded by a double membrane: nucleus, mitochondria, chloroplasts. In the nucleus, along with the membrane and nuclear juice, the nucleolus and chromosomes are found. The cytoplasm is represented by the main substance (matrix, hyaloplasm) in which inclusions and organelles are distributed.
A large number of organelles are limited to a single membrane (lysosomes, vacuoles, etc.)
In a eukaryotic cell, organelles of general and special significance are distinguished. For example: general meaning - nucleus, mitochondria, ER, etc.; of special importance - microvilli of the suction surface of the epithelial cells of the intestine, cilia of the epithelium of the trachea and bronchi.
Mitosis is a characteristic mechanism of reproduction in generations of genetically similar cells.
The sexual process is characteristic. True sex cells are formed - gametes.
Not capable of fixing free nitrogen.
Aerobic respiration occurs in mitochondria.
Photosynthesis takes place in chloroplasts containing membranes, which are usually arranged in grana.
Eukaryotes are represented by unicellular, filamentous and truly multicellular forms.

The main structural components of a eukaryotic cell

organelles

Core. Structure and functions.

The cell has a nucleus and cytoplasm. cell nucleus consists of a membrane, nuclear juice, nucleolus and chromatin. Functional role nuclear envelope consists in the separation of the genetic material (chromosomes) of the eukaryotic cell from the cytoplasm with its numerous metabolic reactions, as well as the regulation of bilateral interactions between the nucleus and the cytoplasm. The nuclear envelope consists of two membranes separated by a perinuclear (perinuclear) space. The latter can communicate with the tubules of the cytoplasmic reticulum.

The nuclear envelope is pierced by a sill with a diameter of 80-90nm. The pore region or pore complex with a diameter of about 120 nm has a certain structure, which indicates a complex mechanism for the regulation of nuclear-cytoplasmic movements of substances and structures. The number of pores depends on the functional state of the cell. The higher the synthetic activity in the cell, the greater their number. It is estimated that in lower vertebrates in erythroblasts, where hemoglobin is intensively formed and accumulated, there are about 30 pores per 1 μm 2 of the nuclear envelope. In mature erythrocytes of these animals that retain nuclei, up to five pores remain per 1 μg of the membrane, i.e. 6 times less.

In the region of the feather complex, the so-called dense plate - a protein layer that underlies the entire length of the inner membrane of the nuclear membrane. This structure primarily performs a supporting function, since in its presence the shape of the nucleus is preserved even if both membranes of the nuclear envelope are destroyed. It is also assumed that the regular connection with the substance of the dense plate contributes to the ordered arrangement of chromosomes in the interphase nucleus.

basis nuclear juice, or matrix, make up proteins. Nuclear juice forms the internal environment of the nucleus, and therefore it plays an important role in ensuring the normal functioning of the genetic material. The composition of nuclear juice contains filamentous, or fibrillar, proteins, with which the performance of the support function is associated: the matrix also contains the primary products of transcription of genetic information - heteronuclear RNA (hnRNA), which are processed here, turning into mRNA (see 3.4.3.2).

nucleolus is the structure in which formation and maturation take place ribosomal RNA (rRNA). rRNA genes occupy certain areas (depending on the type of animal) of one or more chromosomes (in humans, 13-15 and 21-22 pairs) - nucleolar organizers, in the area of \u200b\u200bwhich the nucleoli are formed. Such regions in metaphase chromosomes look like constrictions and are called secondary stretches. With Using an electron microscope, filamentous and granular components are revealed in the nucleolus. The filamentous (fibrillar) component is represented by complexes of protein and giant RNA precursor molecules, from which smaller molecules of mature rRNA are then formed. In the process of maturation, fibrils are transformed into ribonucleoprotein grains (granules), which represent the granular component.

Chromatin structures in the form of lumps, scattered in the nucleoplasm, are an interphase form of the existence of cell chromosomes

cytoplasm

AT cytoplasm distinguish between the main substance (matrix, hyaloplasm), inclusions and organelles. The main substance of the cytoplasm fills the space between the plasmalemma, nuclear membrane and other intracellular structures. An ordinary electron microscope does not reveal any internal organization in it. The protein composition of the hyaloplasm is diverse. The most important of the proteins are represented by enzymes of haicolysis, metabolism of sugars, nitrogenous bases, amino acids and lipids. A number of hyaloplasmic proteins serve as subunits from which structures such as microtubules are assembled.

The main substance of the cytoplasm forms the true internal environment of the cell, which unites all intracellular structures and ensures their interaction with each other. The fulfillment of the unifying and scaffolding functions by the matrix can be associated with the microtrabecular network detected using a super-powerful electron microscope, formed by thin fibrils 2-3 nm thick and penetrating the entire cytoplasm. Through the hyaloplasm, a significant amount of intracellular movements of substances and structures is carried out. The main substance of the cytoplasm should be considered in the same way as a complex colloidal system capable of moving from a sol-like (liquid) state to a gel-like one. In the process of such transitions, work is done. For the functional significance of such transitions, see Sec. 2.3.8.

inclusions(Fig. 2.5) are called relatively unstable components of the cytoplasm, which serve as reserve nutrients (fat, glycogen), products to be removed from the cell (secret granules), ballast substances (some pigments).

Organelles - These are permanent structures of the cytoplasm that perform vital functions in the cell.

Isolate organelles general meaning and special. The latter are present in a significant amount in cells specialized to perform a certain function, but in a small amount they can also be found in other cell types. These include, for example, microvilli of the suction surface of the intestinal epithelial cell, cilia of the epithelium of the trachea and bronchi, synaptic vesicles that transport substances that carry nerve excitation from one nerve cell to another or a cell of the working organ, myofibrils, on which muscle contraction depends. A detailed consideration of special organelles is included in the task of the course of histology.

Organelles of general importance include elements of the tubular and vacuolar system in the form of a rough and smooth cytoplasmic reticulum, a lamellar complex, mitochondria, ribosomes and polysomes, lysosomes, peroxisomes, microfibrils and microtubules, centrioles of the cell center. Chloroplasts are also isolated in plant cells, in which photosynthesis takes place.

tubular and vacuolar system formed by communicating or separate tubular or flattened (cistern) cavities, limited by membranes and spreading throughout the cytoplasm of the cell. Often, tanks have bubble-like extensions. In this system, there are rough and smooth cytoplasmic reticulum(see Fig. 2.3). A feature of the structure of a rough network is that polysomes are attached to its membranes. Because of this, it performs the function of synthesizing a certain category of proteins that are mainly removed from the cell, for example, secreted by gland cells. In the area of the rough network, the formation of proteins and lipids of cytoplasmic membranes, as well as their assembly. Densely packed into a layered structure, cisterns of a rough network are the sites of the most active protein synthesis and are called ergastoplasm.

The membranes of the smooth cytoplasmic reticulum are devoid of polysomes. Functionally, this network is associated with the metabolism of carbohydrates, fats and other non-protein substances, such as steroid hormones (in the gonads, adrenal cortex). Through the tubules and cisterns, substances move, in particular, the material secreted by the glandular cell, from the site of synthesis to the packing area into granules. In areas of liver cells rich in smooth network structures, harmful toxic substances and some drugs (barbiturates) are destroyed and rendered harmless. In the vesicles and tubules of the smooth network of striated muscles, calcium ions are stored (deposited), which play an important role in the contraction process.

Ribosome - it is a rounded ribonucleoprotein particle with a diameter of 20-30nm. It consists of small and large subunits, the combination of which occurs in the presence of messenger (messenger) RNA (mRNA). One mRNA molecule usually combines several ribosomes like a string of beads. Such a structure is called polysome. Polysomes are freely located in the ground substance of the cytoplasm or attached to the membranes of the rough cytoplasmic reticulum. In both cases, they serve as a site for active protein synthesis. Comparison of the ratio of the number of free and membrane-attached polysomes in embryonic undifferentiated and tumor cells, on the one hand, and in specialized cells of an adult organism, on the other hand, led to the conclusion that proteins are formed on hyaloplasmic polysomes for their own needs (for "home" use) of this cell, while on the polysomes of the granular network proteins are synthesized that are removed from the cell and used for the needs of the body (for example, digestive enzymes, breast milk proteins).

Golgi lamellar complex formed by a collection of dictyosomes ranging from several tens (usually about 20) to several hundreds and even thousands per cell.

Dictyosome(Fig. 2.6, BUT) is represented by a stack of 3-12 flattened disk-shaped cisterns, from the edges of which vesicles (vesicles) are laced off. Limited to a certain area (local) expansion of tanks give larger bubbles (vacuoles). In differentiated cells of vertebrates and humans, dictyosomes are usually assembled in the perinuclear zone of the cytoplasm. In the lamellar complex, secretory vesicles or vacuoles are formed, the contents of which are proteins and other compounds to be removed from the cell. At the same time, the precursor of the secret (prosecret), which enters the dictyosome from the synthesis zone, undergoes some chemical transformations in it. It also separates (segregates) in the form of "portions", which are here dressed in a membrane sheath. Lysosomes are formed in the lamellar complex. In dictyosomes, polysaccharides are synthesized, as well as their complexes with proteins (glycoproteins) and fats (glycolipids), which can then be found in the glycocalyx of the cell membrane.

The shell of mitochondria consists of two membranes that differ in chemical composition, a set of enzymes, and functions. The inner membrane forms invaginations of leaf-shaped (cristae) or tubular (tubules) shape. The space bounded by the inner membrane is matrix organelles. Using an electron microscope, grains with a diameter of 20-40 nm are detected in it. They accumulate calcium and magnesium ions, as well as polysaccharides, such as glycogen.

The matrix contains its own organelle protein biosynthesis apparatus. It is represented by 2 copies of a circular and histone-free (as in prokaryotes) DNA molecule, ribosomes, a set of transport RNA (tRNA), enzymes for DNA replication, transcription and translation of hereditary information. In terms of its main properties: the size and structure of ribosomes, the organization of its own hereditary material, this apparatus is similar to that of prokaryotes and differs from the apparatus of protein biosynthesis in the cytoplasm of a eukaryotic cell (which confirms the symbiotic hypothesis of the origin of mitochondria; see § 1.5). Genes of their own DNA encode nucleotide sequences mitochondrial rRNA and tRNA, as well as the amino acid sequences of some proteins of the organelle, mainly its inner membrane. The amino acid sequences (primary structure) of most mitochondrial proteins are encoded in the DNA of the cell nucleus and are formed outside the organelle in the cytoplasm.

The main function of mitochondria is to enzymatically extract energy from certain chemicals (by oxidizing them) and to store energy in a biologically usable form (by synthesizing adenosine triphosphate-ATP molecules). In general, this process is called oxidative(disbandment. The components of the matrix and the inner membrane are actively involved in the energy function of mitochondria. It is with this membrane that the electron transport chain (oxidation) and ATP synthetase are connected, catalyzing the oxidation-related phosphorylation of ADP to ATP. Among the side functions of mitochondria, one can name participation in the synthesis of steroid hormones and some amino acids (glutamine).

Lysosomes(Fig. 2.6, AT) are bubbles with a diameter of usually 0.2-0.4 μm, which contain a set of acid hydrolase enzymes that catalyze the hydrolytic (in an aqueous medium) cleavage of nucleic acids, proteins, fats, polysaccharides at low pH values. Their shell is formed by a single membrane, sometimes covered on the outside with a fibrous protein layer (on the electron diffraction patterns "bordered" vesicles). The function of lysosomes is the intracellular digestion of various chemical compounds and structures.

Primary lysosomes(diameter 100nm) are called inactive organelles, secondary - organelles in which digestion takes place. Secondary lysosomes are formed from primary ones. They are subdivided into heterolysosomes(phagolysosomes) and autolysosomes(cytolysosomes). In the first (Fig. 2.6, G) the material entering the cell from the outside is digested by pinocytosis and phagocytosis, secondly, the cell's own structures that have completed their function are destroyed. Secondary lysosomes, in which the digestion process is completed, are called residual bodies(telolisosomes). They lack hydrolases and contain undigested material.

Microbodies make up a group of organelles. These are vesicles with a diameter of 0.1-1.5 μm limited by one membrane with a fine-grained matrix and often crystalloid or amorphous protein inclusions. This group includes, in particular, peroxisomes. They contain oxidase enzymes that catalyze the formation of hydrogen peroxide, which, being toxic, is then destroyed by the action of the peroxidase enzyme. These reactions are included in various metabolic cycles, for example, in the exchange of uric acid in the cells of the liver and kidneys. In the liver cell, the number of peroxisomes reaches 70-100.

Organelles of general importance also include some permanent structures of the cytoplasm, devoid of membranes. microtubules(fig.2.6, D) - tubular formations of various lengths with an outer diameter of 24 nm, a lumen width of 15 nm, and a wall thickness of about 5 nm. They are found in the free state in the cytoplasm of cells or as structural elements of flagella, cilia, mitotic spindle, centrioles. Free microtubules and microtubules of cilia, flagella and centrioles have different resistance to damaging effects, such as chemical (colchicine). Microtubules are built from stereotypical protein subunits by polymerization. In a living cell, polymerization processes proceed simultaneously with depolymerization processes. The ratio of these processes determines the number of microtubules. In the free state, microtubules perform a supporting function, determining the shape of cells, and are also factors in the directed movement of intracellular components.

Microfilaments(Fig. 2.6, E) are called long, thin formations, sometimes forming bundles and found throughout the cytoplasm. There are several different types of microfilaments. actin microfilaments due to the presence of contractile proteins (actin) in them, they are considered as structures that provide cellular forms of movement, for example, amoeboids. They are also credited with a frame role and participation in the organization of intracellular movements of organelles and sections of hyaloplasm.

Along the periphery of cells under the plasmalemma, as well as in the perinuclear zone, bundles of microfilaments 10 nm thick are found - intermediate filters. In epithelial, nerve, glial, muscle cells, fibroblasts, they are built from different proteins. Intermediate filaments apparently perform a mechanical, frame function.

Actin microfibrils and intermediate filaments, like microtubules, are built from subunits. Because of this, their number depends on the ratio of polymerization and depolymerization processes.

For animal cells, parts of plant cells, fungi and algae, cell center, which contains centrioles. Centriole(under the electron microscope) looks like a "hollow" cylinder with a diameter of about 150 nm and a length of 300-500 nm. Its wall is formed by 27 microtubules grouped into 9 triplets. The function of centrioles is the formation of mitotic spindle filaments, which are also formed by microtubules. Centrioles polarize the process of cell division, ensuring the separation of sister chromatids (chromosomes) in the anaphase of mitosis.

The eukaryotic cell has a cellular skeleton (cytoskeleton) of intracellular fibers (Koltsov) - the beginning of the 20th century, it was rediscovered at the end of 1970. This structure allows the cell to have its shape, sometimes changing it. The cytoplasm is in motion. The cytoskeleton is involved in the process of transfer of organelles, is involved in cell regeneration.

Mitochondria are complex formations with a double membrane (0.2-0.7 microns) and different shapes. The inner membrane has cristae. The outer membrane is permeable to almost all chemicals, while the inner membrane is permeable only to active transport. Between the membranes is the matrix. Mitochondria are located where energy is needed. Mitochondria have a system of ribosomes, a DNA molecule. Mutations may occur (more than 66 diseases). As a rule, they are associated with insufficient ATP energy, often associated with cardiovascular insufficiency, pathologies. The number of mitochondria is different (in a trypanosome cell - 1 mitochondria). The amount depends on age, function, tissue activity (liver - more than 1000).

Lysosomes are bodies surrounded by an elementary membrane. Contain 60 enzymes (40 lysosomal, hydrolytic). Inside the lysosome is a neutral environment. They are activated by low pH values, leaving the cytoplasm (self-digestion). Lysosome membranes protect the cytoplasm and cells from destruction. They are formed in the Golgi complex (intracellular stomach, they can process cells that have worked out their structures). There are 4 kinds. 1-primary, 2-4 - secondary. Substance enters the cell by endocytosis. The primary lysosome (storage granule) with a set of enzymes absorbs the substance and a digestive vacuole is formed (with complete digestion, cleavage goes to low molecular weight compounds). Undigested residues remain in residual bodies, which can accumulate (lysosomal storage diseases). Residual bodies that accumulate in the embryonic period lead to gargaleism, deformities, and mucopolysaccharidoses. Autophagic lysosomes destroy the cell's own structures (unnecessary structures). May contain mitochondria, parts of the Golgi complex. Often formed during starvation. May occur when exposed to other cells (erythrocytes).

The cytoplasm is the internal contents of the cell and consists of the main substance, or hyaloplasm, and various intracellular structures located in it.

Hyaloplasm (matrix) is an aqueous solution of inorganic and organic substances that can change its viscosity and is in constant motion. The ability to move, or flow of the cytoplasm, is called cyclosis. The matrix is an active medium in which many chemical and physiological processes take place and which unites all the components of the cell into a single system.

The cytoplasmic structures of the cell are represented by inclusions and organelles.

Organelles are permanent and indispensable components of most cells, having a specific structure and performing vital functions. Organoids are of general purpose and special purpose.

Organelles of general importance are present in all cells and, depending on the structural features, are divided into non-membrane, single-membrane and two-membrane.

Organelles of special significance are present only in the cells of certain tissues; for example, myofibrils in muscle tissues, neurofibrils in nervous tissue.

non-membrane organelles.

This group includes ribosomes, microtubules and microfilaments, as well as the cell center.

RIBOSOMES.

Ribosomes - very small organelles, present in all cell types. They have a rounded shape, consist of approximately equal mass amounts of rRNA and protein and are represented by two subunits: large and small. Between the subunits is a space where the mRNA attaches.

In cells, ribosomes are freely localized in the cytoplasm, on EPS membranes, in the mitochondrial matrix, on the outer membrane of the nucleus, and in plants in plastids.

The function of ribosomes is the assembly of protein molecules.

During active protein synthesis, polyribosomes are formed. Polyribosomes- a complex of ribosomes (from 5 to 70 ribosomes). There is a connection between individual ribosomes, which is carried out with the help of mRNA molecules.

Rice. 5. The structure of the ribosome (scheme)

1- small subunit; 2 - i-RNA; 3 - large subunit of 4-rRNA

MICROTUBES AND MICROFILAMENTS

Microtubules and microfilaments filamentous structures made up of various contractile proteins. Microtubules look like long hollow cylinders, the walls of which are composed of proteins - tubulins. Microfilaments are very thin, long, filamentous structures composed of actin and myosin. Microtubules and microfilaments penetrate the entire cytoplasm of the cell, forming its cytoskeleton, causing cyclosis, intracellular movements of organelles, chromosome segregation during the division of nuclear material. In addition to free microtubules penetrating the cytoplasm, cells have microtubules organized in a certain way that form the centrioles of the cell center, basal bodies, cilia and flagella.

CELL CENTER

Cell center or centrosome- usually located near the nucleus, consists of two centrioles located perpendicular to each other. Each centriole has the form of a hollow cylinder, the wall of which is formed by 9 triplets of microtubules. There are no microtubules in the center. Therefore, the centriole microtubule system can be described by the formula (9×3)+0.

During the preparation of the cell for division, doubling occurs - duplication centrioles: maternal and daughter diverge to the poles of the cell, outlining the direction of future division, near each, a new centriole is formed from microtubules of the cytoplasm. The main functions of the cell center are:

1) participation in the processes of cell division, the divergence of centrioles determines the orientation of the division spindle and the movement of chromosomes;

2) the structure and function of cilia and flagella (basal bodies) is associated with this organoid; thus, centrioles are associated with the processes of movement in the cell.

Single membrane organelles

These include the endoplasmic reticulum, the Golgi apparatus, lysosomes, and peroxisomes.

5.2.1 Endoplasmic reticulum (ER).

It is a network in the inner layers of the cytoplasm (endoplasm) - an endoplasmic reticulum, which is a complex system tubules, tubules and cisterns bounded by membranes.

There are EPS (EPR):

Smooth (agranular) (does not contain ribosomes on membranes)	Rough (granular) (on membranes - ribosomes)
1. Synthesis of glycogen and lipids (sebaceous glands, liver). 2. Accumulation of synthesis products. 3. Secret transport.	1. Protein synthesis (protein gland cells). 2. Participation in secretory processes, secretion transport. 3. Accumulation of synthesis products.
	4. Provides communication with cell organelles. 5. Provides transport of secrets to cell organelles. 6. Provides communication between the nucleus and cellular organelles and the cytoplasmic membrane. 7. Provides circulation of various substances through the cytoplasm. 8. Participation in pinocytosis (transport of various substances that enter the cell from the outside).

The greatest development of EPS is characteristic of secretory cells. EPS is weakly developed in spermatozoa.

The formation of EPS occurs during cell division from the growths of the outer cytoplasmic membrane and nuclear membrane, is transmitted from cell to cell during cell division.

GOLGI COMPLEX

Golgi complex opened in 1898 by Golgi.

The form of the complex can be in the form of a network around the nucleus, in the form of a cap or belt around the nucleus, in the form of individual elements - rounded, sickle-shaped bodies called dictyosomes.

The Golgi complex consists of three elements that can pass one into another and are interconnected with each other:

1) a system of flat tanks, arranged in packs of five to eight, in the form of a stack of coins and tightly adjacent to each other;

2) a system of tubules extending from the tanks, anastomosing with each other and forming a network;

3) large and small vesicles that close the end sections of the tubules.

This organoid is most well developed in glandular cells, for example, in leukocytes and oocytes, as well as in other cells that produce protein products, polysaccharides and lipids.

Weak development of the Golgi complex is observed in undifferentiated and tumor cells.

Composition: phospholipids, proteins, enzymes for the synthesis of polysaccharides and lipids.

1) participation in the secretory activity of the cell;

2) the accumulation of finished or almost finished products;

3) transportation of secretion products throughout the cell through a system of tubules and vesicles;

4) condensation of secretory granules (osmotic removal of water);

5) isolation and accumulation of substances that are toxic to cells from outside (toxins, anesthetic substances), which are then removed from the cell;

6) formation of yolk grains in oocytes;

7) formation of cell partitions (in plant cells).

The Golgi complex during cell division is transferred from the mother to the daughter.

LYSOSOME

They perform the function of intracellular digestion of food macromolecules and foreign components entering the cell during phago- and pinocytosis, providing the cell with additional raw materials for chemical and energy processes. To carry out these functions, lysosomes contain about 40 hydrolytic enzymes - hydrolases that destroy proteins, nucleic acids, lipids, carbohydrates at acidic pH (proteinases, nucleases, phosphatases, lipases). There are primary lysosomes, secondary lysosomes (phagolysosomes and autophagosomes) and residual bodies. Primary lysosomes are microvesicles detached from the cavities of the Golgi apparatus, surrounded by a single membrane and containing a set of enzymes. After the fusion of primary lysosomes with some substrate to be cleaved, various secondary lysosomes are formed. An example of secondary lysosomes are the digestive vacuoles of protozoa. Such lysosomes are called phagolysosomes, or heterophagosomes. If the fusion occurs with the altered organelles of the cell itself, then autophagosomes are formed. Lysosomes, in the cavities of which undigested products accumulate, are called telolisosomes or residual bodies.

EPS, the Golgi apparatus, and lysosomes are functionally related intracellular structures separated from the cytoplasm by a single membrane. They constitute a single tubular-vacuolar system of the cell.

Peroxisomes

They have an oval shape. Crystal-like structures are located in the central part of the matrix. The matrix contains enzymes for the oxidation of amino acids, during which hydrogen peroxide is formed. The enzyme catalase is also present, which destroys peroxide. (Characteristic of liver and kidney cells)

Double membrane organelles

Mitochondria

The shape of the mitochondria can be oval, rod-shaped, filamentous, highly branched. The forms of mitochondria can change from one to another with changes in pH, osmotic pressure, and temperature. The shape can be different in different cells, and in different parts of the same cell.

Outside, mitochondria are bounded by a smooth outer membrane. The inner membrane forms numerous outgrowths - cristae. The internal content of mitochondria is called the matrix. Mitochondria are semi-autonomous organelles, since they contain their own apparatus for protein biosynthesis (circular DNA, RNA, ribosomes, amino acids, enzymes).

Matrix- the substance is denser than the cytoplasm, homogeneous.

krist a lot in the liver cells, they are located tightly relative to each other; less in muscles.

Fig.7. The structure of the mitochondria (scheme)

1- smooth outer membrane; 2 - inner membrane; 3 - cristae; 4 - matrix (and it contains a circular DNA molecule, many ribosomes, enzymes).

The size of mitochondria varies from 0.2 to 20 microns.

The number of mitochondria is different in different cell types: from 5-7 to 2500, depending on the functional activity of the cells. A large number of mitochondria in liver cells, working muscles (more in young than in old ones).

The location of mitochondria can be uniform throughout the cytoplasm, such as in epithelial cells, nerve cells, protozoan cells, or uneven, for example, in the area of the most active cellular activity. In secretory cells, these are the areas where the secret is produced, in the cells of the heart muscle and gametes (surround the nucleus). A structural connection between mitochondria and the cell nucleus was found in the periods preceding cell division. It is believed that during this period, the processes of metabolism and energy are actively taking place and it is carried out according to structures resembling tubes.

Chemical composition: proteins - 70%, lipids - 25%, nucleic acids (DNA, RNA - slightly), vitamins A, B 12, B 6, K, E, enzymes.

Mitochondria are the most sensitive organelles to the effects of various factors: drugs, fever, poisons lead to swelling, an increase in the volume of mitochondria, their matrix liquefies, the number of cristae decreases, and folds appear on the outer membrane. These processes lead to disruption of cellular respiration and can become irreversible with frequent and extreme exposures.

In mitochondria, ATP is synthesized as a result of the processes of oxidation of organic substrates and ADP phosphorylation and the synthesis of steroid hormones.

In the process of evolution, different cells adapted to living in different conditions and performing specific functions. This required the presence in them of special organelles, which are called specialized.

Such organelles are present only in the cells of certain tissues, for example, myofibrils - in muscle, neurofibrils - in nerve, tono-fibrils, cilia and flagella - in epithelial.

INCLUSIONS

Unlike organelles, inclusion are temporary structures that appear in the cell at certain periods of the cell's life. The main place of localization of inclusions is the cytoplasm, but sometimes the nucleus.

Inclusions are products of cellular metabolism, they can take the form of granules, grains, drops, vacuoles and crystals; are used either by the cell itself as needed, or serve for the entire macroorganism.

Inclusions classified according to their chemical composition:

fatty:	carbohydrate:	protein:	pigmented:
1) in any cell in the form of droplets of fat; 2) white fat - specialized adipose tissue of adults; 3) brown fat - specialized adipose tissue of embryos; 4) as a result of pathological processes - fatty degeneration of cells (liver, heart); 5) in plants - seeds contain up to 70% inclusions;	1) glycogen - in skeletal muscle cells, liver, neurons; 2) in cells of endoparasites (anaerobic type of respiration); 3) starch - in plant cells;	1) in eggs, liver cells, protozoa;	1) lipofuscin - aging pigment; 2) lipochromes - in the cortical substance-venapdrenal and corpus luteum of the ovary; 3) retinin - visual purple of the eye; 4) melanin - in pigment cells; 5) hemoglobin - respiratory - in erythrocytes;
	secretory: can be proteins, fats, carbohydrates, or mixed and are located in the cells of the corresponding glands: 1) sebaceous gland; 2) endocrine glands; 3) glands of the digestive system; 4) mammary glands; 5) mucus in goblet cells; 6) essential oils of plants.

CELL NUCLEUS

The cell nucleus is involved in the differentiation of cells in shape, number, location, and size. The shape of the nucleus is often related to the shape of the cell, but it can also be completely wrong. In spherical, cubic, and polyhedral cells, the nucleus is usually spherical; in cylindrical, prismatic and spindle-shaped - the shape of an ellipse (smooth myocyte).

Fig 8. Smooth myocyte

An example of an irregularly shaped nucleus is the nuclei of leukocytes (segmented - segmented neutrophilic leukocyte). Blood monocytes have a bean-shaped nucleus.

Rice. nine. blood monocyte Rice. ten Segmented

neutrophilic leukocyte

Most cells have one nucleus. But there are binuclear cells: liver cells, hepatocytes and cartilage chondrocytes, and multinuclear cells: osteoclasts of bone tissue and megakaryocytes of the red bone marrow - up to 100 nuclei. Nuclei are especially numerous in symplasts and syncytia (striated muscle fibers and reticular tissue), but these formations are not actually cells.

Fig.11. Hepatocyte Rice. 12.Megakariacite

The arrangement of nuclei is individual for each cell type. Usually in undifferentiated cells, the nucleus is located in the geometric center of the cell. With maturation, accumulation of reserve nutrients and organelles, the nucleus shifts to the periphery. There are cells in which the nucleus occupies a sharply eccentric position. The most striking example of this is white fat cells, adipocytes, in which almost the entire volume of the cytoplasm is occupied by a drop of fat. In any case, no matter how the nucleus is located in the cell, it is almost always surrounded by a zone of undifferentiated cytoplasm.

Rice. 13Adipocytes

The size of the nucleus depends on the type of cell and is usually directly proportional to the volume of the cytoplasm. The ratio between the volume of the nucleus and the cytoplasm is usually expressed by the so-called nuclear-plasmic (N-C) Hertwig ratio: with an increase in the volume of the cytoplasm, the volume of the nucleus also increases. The moment of onset of cell division, apparently, is determined by a change in the R-C ratio and is due to the fact that only a certain volume of the nucleus is able to control a certain volume of the cytoplasm. Usually larger nuclei are found in young, tumor cells, cells preparing for division. At the same time, the volume of the nucleus is a feature characteristic of each tissue. There are tissues whose cells have a small nucleus relative to the volume of the cytoplasm, these are the so-called cells cytoplasmic type. These include most cells of the body, for example, all types of epithelia.

Others - have a large nucleus, which occupies almost the entire cell and a thin rim of the cytoplasm - cells nuclear such as blood lymphocytes.

Fig.16 The structure of the nucleus (diagram)

1- ribosomes on the outer membrane; 2 - nuclear pores; 3 - outer membrane; 4 - inner membrane; 5 - nuclear envelope; (karyolemma, nucleolemma); 6 - slit-like perinuclear space; 7 - nucleolus;

8 - nuclear juice (karyoplasm, nucleoplasm); 9 - heterochromatin;

10 - euchromatin.

nuclear envelope formed by two elementary biological membranes, between which there is a slit-like perinuclear space. The nuclear envelope serves to delimit the intranuclear space from the cytoplasm of the cell. It is not continuous and has the smallest holes - pores. The nuclear pore is formed by the fusion of nuclear membranes and is a complexly organized globular-fibrillar structure that fills the perforation in the nuclear envelope. This so-called nuclear pore complex. Along the border of the hole there are three rows of granules (eight in each). The first row is adjacent to the intranuclear space, the second to the cytoplasm, and the third is located between them. Fibrillar processes depart from the granules, which are connected in the center with the help of the granule and create a septum, diaphragm across the pore. The number of pores is not constant and depends on the metabolic activity of the cell.

nuclear juice- an uncolored mass that fills the entire internal space of the nucleus between its components and is a colloidal system and has turgor.

Nucleoli- one or more steroid bodies, often quite large (in neurocytes and oocytes). Nucleoli - nucleoli- the most dense structure of the nucleus, they stain well with basic dyes, as they are rich in RNA. It is heterogeneous in its structure, has a fine-grained or fine-fibered structure. Serves as a place of education ribosome.

Chromatin- zones of dense substance, which are well perceived by dyes, are characteristic of a non-dividing cell. Chromatin has a different state of aggregation - during cell division, it turns by condensation and spiralization into chromosomes. Each chromosome has centromere- the place of attachment to the threads of the spindle of division during mitosis of the centromere divides the chromosome into two arms.

In addition to the centromere (primary constriction), the chromosome may have secondary constriction and separated by her satellite. On the outside, each chromosome is covered pellicle, under which there is a protein matrix. In the matrix are chromatids. Chromatids are made up of lameness, and those from filaments. The set of chromosomes in each organism is chromosome set.

Fig17. Chromosome structure (diagram)

1 - centromere (primary constriction); 2-shoulders; 3 - secondary constriction; 4-satellite; 5 - pellicle; 6 - protein matrix; 7 - chromatin

REPRODUCTION OF CELLS.

All living organisms are made up of cells. In the process of vital activity, part of the cells of the body wears out, ages and dies. The only way to form cells is the division of the previous ones. Cell division is a vital process for all organisms.

Life (cell) cycle.

The life of a cell from the moment of its origin as a result of the division of the maternal cell to its own division or death is called life (cell) cycle. An essential component of the cell cycle is mitotic cycle, including the period of cell preparation for division and division itself. Cell preparation for division, or interphase, is a significant part of the time of the mitotic cycle and consists of periods:

1. Presynthetic (postmitotic) G1 - occurs immediately after cell division. Biosynthesis processes take place in the cells, new organelles are formed. The young cell is growing. This period is the most variable in duration.

2. Synthetic S is the main one in the mitotic cycle. DNA replication takes place. Each chromosome becomes double-stranded, that is, it consists of two chromatids - identical DNA molecules. In addition, the cell continues to synthesize RNA and proteins. In dividing mammalian cells, it lasts about 6-10 hours.

3. Postsynthetic (premitotic) G2 is relatively short, in mammalian cells it is about 2-5 hours. At this time, the number of centrioles and mitochondria doubles, active metabolic processes take place, proteins and energy are accumulated for the upcoming division. The cell starts dividing.

7.2 CELL DIVISION.

Three methods of eukaryotic cell division have been described:

1) amitosis (direct division),

2) mitosis (indirect division).

3) meiosis (reduction division).

7.2.1 Amitosis- cell division without spiralization of chromosomes, arose earlier than mitosis. In this way they reproduce prokaryotes, highly specialized and degrading cells. At the same time, the nuclear membrane and nucleoli do not disappear, the chromosomes remain spiralized.

Types of amitosis:

1) lacing(characteristic of bacteria)

2) fragmentation(megakaryoblast, megakaryocyte)

3)budding(platelet buds from megakaryocytes)

By distribution genetic material

Irradiation, tissue degeneration, and the action of various agents that disrupt the entry of cells into mitosis lead to division without a mitotic apparatus.

Mitosis

It is characterized by the destruction of the nuclear membrane and nucleoli, the spiralization of chromosomes. In mitosis, there are prophase, metaphase, anaphase and telophase.

Fig.18. Diagram of mitosis

I. Prophase:

1) The shape of the cell becomes round, its contents become more viscous, the chromosomes take the form of long thin threads twisted inside the nucleus. Each chromosome is made up of two chromatids.

2) Chromatids gradually shorten and approach the nuclear membrane, which is a sign of the beginning of the destruction of the karyolemma.

3) The spindle develops: the centrioles diverge towards the poles and double, between them the fission spindle threads are formed.

4) The destruction of the nuclear membrane occurs, in the center of the cell a zone of liquid cytoplasm is formed, where the chromosomes rush.

late metaphase

Chromosomes line up in the equatorial plane, forming metaphyseal plate. Spindle threads are attached to the centromeres of chromosomes.

There are two types of spindle fibers: some of them are associated with chromosomes and are called chromosomal, while others stretch from pole to pole and are called continuous.

maternal

IV. Telophase.

The migration of two daughter groups of chromosomes to opposite poles of the cell is completed. reconstruction nuclei and decondensation chromosomes, they despiralize, the karyolemma is restored, nucleoli appear. Nuclear fission is completed.

Begins cytokinesis (cytotomy)- the process of ligation and division of the cytoplasm with the formation of constriction. There is a "boiling" of the cell surface due to its intensive growth. The cytoplasm loses its viscosity, the centrioles lose their activity, the organelles are divided approximately in half between the daughter cells.

Fig.24 Cytokinesis

Mitosis types:

1) Any tissue is a self-regulating system, in connection with this, the number of cells that died in the tissue is balanced by the number of their formed.

2) Exist daily allowance rhythms of mitotic activity. The greatest mitotic activity coincides with periods of tissue rest, and an increase in tissue function leads to inhibition of mitoses (in nocturnal animals - in the early morning, and in animals leading a daytime lifestyle - at night).

3) The inhibitory effect on mitotic activity is exerted by stress hormones: adrenaline and norepinephrine, and the stimulating effect is exerted by growth hormone. Changes in mitotic activity occur due to changes in the duration of interphase. Each cell initially has the ability to divide, but under certain conditions this ability inhibited. Inhibition can be of varying degrees, up to irreversible.

cell lifespan can be thought of as a period from one division to another. In stable cell populations, in which there is practically no cell reproduction, their life span is maximum (liver, nervous system).

Endoreproduction- all cases when chromosome reduplication or DNA replication occurs, cell division does not occur. This leads to polyplodia, an increase in the volume of the nucleus and cells. It can occur with violations of the mitotic apparatus, it is observed both in normal and pathological conditions. It is characteristic of cells of the liver, urinary tract.

Endomitosis proceeds with an indestructible nuclear envelope. Chromosome reduplication occurs as in normal division, resulting in the formation of giant chromosomes. All the figures characteristic of mitosis are observed, but they occur inside the nucleus. Distinguish endoprophase,endometaphase,endoanaphase,endothelophase. Since the kernel shell is preserved, the result is polyploid cell. The significance of endomitosis lies in the fact that during it the main activity of the cell does not stop.

Cytoplasm- an obligatory part of the cell, enclosed between the plasma membrane and the nucleus and representing a complex heterogeneous structural complex of the cell, consisting of:

The chemical composition of the cytoplasm is diverse. Its basis is water (60-90% of the total mass of the cytoplasm). The cytoplasm is rich in proteins (10-20%, sometimes up to 70% or more of dry weight), which form its basis. In addition to proteins, the cytoplasm may include fats and fat-like substances (2-3%), various organic and inorganic compounds (1.5% each). The cytoplasm is alkaline

One of the characteristic features of the cytoplasm is the constant movement ( cyclosis). It is detected primarily by the movement of cell organelles, such as chloroplasts. If the movement of the cytoplasm stops, the cell dies, since only being in constant motion can it perform its functions.

The main substance of the cytoplasm is hyaloplasm(basic plasma, cytoplasmic matrix) is a colorless, slimy, thick and transparent colloidal solution. It is in it that all metabolic processes take place, it provides the interconnection of the nucleus and all organelles. The liquid part of the hyaloplasm is a true solution of ions and small molecules, in which large molecules of proteins and RNA are in suspension. Depending on the predominance of the liquid part or large molecules in the hyaloplasm, two forms of hyaloplasm are distinguished:

Mutual transitions are possible between them: the gel easily turns into a sol and vice versa.

Organelles (organelles) - permanent cellular structures that ensure the performance of specific functions by the cell. Each organelle has a specific structure and performs specific functions. Depending on the features of the structure, there are:

¨ membrane organelles - having a membrane structure, and they can be:

¨ single-membrane (endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles of plant cells);

¨ two-membrane (mitochondria, plastids);

¨ non-membrane organelles - not having a membrane structure (chromosomes, ribosomes, cell center and centrioles, cilia and flagella with basal bodies, microtubules, microfilaments).

There are organelles characteristic of all cells - mitochondria, cell center, Golgi apparatus, ribosomes, endoplasmic reticulum, lysosomes. They are called organelles of general importance. There are organelles that are characteristic only for certain types of cells, specialized to perform a certain function (for example, myofibrils, which provide muscle fiber contraction). They are called special organelles.

A single-membrane organoid, which is a system of membranes that form tanks and channels, connected to each other and limiting a single internal space - EPR cavity. On the one hand, the membranes are connected to the outer cytoplasmic membrane, on the other hand, to the outer shell of the nuclear membrane. EPR reaches its greatest development in cells with intensive metabolism. On average, it is from 30 to 50% of the total cell volume.

There are three types of EPR:

EPR functions:

Lamellar complex, Golgi complex (Fig. 284). A single-membrane organelle, usually located near the cell nucleus (in animal cells, often near the cell center). Represents a stack of flattened cisterns with expanded edges, which is associated with a system of small single-membrane vesicles (Golgi vesicles). Each stack usually consists of 4-6 tanks. The number of Golgi stacks in a cell ranges from one to several hundred.

Golgi vesicles are mainly concentrated on the side adjacent to the ER and along the periphery of the stacks. It is believed that they transfer proteins and lipids to the Golgi apparatus, the molecules of which, moving from tank to tank, undergo chemical modification. The most important function of the Golgi complex is the removal of various secrets (enzymes, hormones) from the cell, therefore it is well developed in secretory cells. The Golgi apparatus has two different sides:

The outer part of the Golgi apparatus is constantly consumed as a result of the lacing of the bubbles, and the inner part is gradually formed due to the activity of the EPR.

Functions of the Golgi apparatus:

The smallest single-membrane cell organelles, which are vesicles with a diameter of 0.2-0.8 microns, containing about 40 hydrolytic enzymes (proteases, lipases, nucleases, phosphatases) that are active in a slightly acidic environment (Fig. 285). The formation of lysosomes occurs in the Golgi apparatus, where the enzymes synthesized in it come from the EPR. The breakdown of substances by enzymes is called lysis, hence the name of the organoid.

Distinguish:

digestion and lysis of substances entering the cell (therefore they are often called digestive vacuoles):

¨ Digestion products are absorbed by the cytoplasm of the cell, but part of the material remains undigested. The secondary lysosome containing this undigested material is called residual body. By exocytosis, undigested particles are removed from the cell.

¨ The secondary lysosome, which digests the individual components of the cell, is called autophagic vacuole. The parts of the cell to be destroyed are surrounded by a single membrane, usually separated from the smooth ER, and then the resulting membrane sac merges with the primary lysosome, resulting in the formation of an autophagic vacuole.

Sometimes with the participation of lysosomes, self-destruction of the cell occurs. This process is called autolysis. This usually occurs during some processes of differentiation (for example, the replacement of cartilage with bone tissue, the disappearance of the tail in the frog tadpole).

Functions of lysosomes:

Two-membrane organelles of a eukaryotic cell that provide the body with energy (Fig. 286). They are rod-shaped, filiform, spherical, spiral, cup-shaped, etc. shape. The length of the mitochondria is 1.5-10 microns, the diameter is 0.25-1.00 microns.

The number of mitochondria in a cell varies widely, from 1 to 100 thousand, and depends on its metabolic activity. The number of mitochondria can increase by dividing, since these organelles have their own DNA.

The outer membrane of mitochondria is smooth, the inner membrane forms numerous invaginations (ridges) or tubular outgrowths - cristae, which have strictly specific permeability and active transport systems. The number of cristae can vary from several

cells up to several hundreds and even thousands, depending on the functions of the cell.

They increase the surface of the inner membrane, which hosts multienzyme systems involved in the synthesis of ATP molecules.

The inner membrane contains two main types of proteins:

The outer membrane is separated from the inner membrane by an intermembrane space.

The inner space of mitochondria is filled with a homogeneous substance - matrix. The matrix contains circular molecules of mitochondrial DNA, specific mRNA, tRNA and ribosomes (prokaryotic type), which carry out autonomous biosynthesis of some of the proteins that make up the inner membrane. But most of the mitochondrial genes have moved into the nucleus, and the synthesis of many mitochondrial proteins occurs in the cytoplasm. In addition, there are enzymes that form ATP molecules. Mitochondria are capable of reproducing by fission or detachment of small fragments.

Mitochondrial functions:

Non-membrane organelles found in the cells of all organisms. These are small organelles, represented by globular particles with a diameter of about 20 nm (Fig. 287). Ribosomes consist of two subunits of unequal size - large and small, on which they

can dissociate. Ribosomes are made up of proteins and ribosomal RNA (rRNA). rRNA molecules make up 50-63% of the mass of the ribosome and form its structural framework. Most proteins are specifically associated with certain regions of rRNA. Some proteins are only incorporated into ribosomes during protein synthesis.

There are two main types of ribosomes: eukaryotic (with sedimentation constants of the whole ribosome - 80S, small subunit - 40S, large - 60S) and prokaryotic (corresponding to

venously 70S, 30S, 50S). Eukaryotic ribosomes include 4 rRNA molecules and about 100 protein molecules, prokaryotes - 3 rRNA molecules and about 55 protein molecules.

Depending on the location in the cell, there are

During protein biosynthesis, ribosomes can "work" singly or combine into complexes - polyribosomes (polysomes). In such complexes, they are linked to each other by a single mRNA molecule.

Eukaryotic ribosomes are produced in the nucleolus. First, rRNAs are synthesized on nucleolar DNA, which are then covered with ribosomal proteins coming from the cytoplasm, cleaved to the desired size, and form ribosome subunits. There are no fully formed ribosomes in the nucleus. The association of subunits into a whole ribosome occurs in the cytoplasm, as a rule, during protein biosynthesis.

One of the distinguishing features of a eukaryotic cell is the presence in its cytoplasm of skeletal formations in the form of microtubules and bundles of protein fibers. The elements of the cytoskeleton, closely associated with the outer cytoplasmic membrane and the nuclear membrane, form complex interlacings in the cytoplasm.

The cytoskeleton is formed by the microtrabecular system, microtubules and microfilaments.

The cytoskeleton determines the shape of the cell, participates in the movements of the cell, in the division and movements of the cell itself, in the intracellular transport of organelles and individual compounds. Microfilaments also perform the function of cell reinforcement.

The microtrabecular system is a network of thin fibrils - trabeculae (crossbeams), at the points of intersection or connection of the ends of which ribosomes are located.

The microtrabecular system is a dynamic structure: under changing conditions, it can disintegrate and reassemble.

Functions of the microtrabecular grid:

The wall of microtubules is mainly built from helically stacked tubulin protein subunits. It is believed that centrioles, basal bodies of flagella and cilia, and centromeres of chromosomes can play the role of a matrix (organizer of microtubules).

Functions of microtubules:

The centriole is a cylinder (0.3 μm long and 0.1 μm in diameter), the wall of which is formed by nine groups of three fused microtubules (9 triplets) interconnected at certain intervals by cross-links. Often centrioles are paired, where they are located at right angles to each other. If the centriole lies at the base of the cilium or flagellum, then it is called basal body.

Almost all animal cells have a pair of centrioles, which are the middle element centrosome, or cell center(Fig. 288). Before dividing, centrioles diverge to opposite poles and near each of them

a daughter centriole is formed. From centrioles located at different poles of the cell, microtubules are formed that grow towards each other. They form a mitotic spindle, which contributes to the uniform distribution of genetic material between daughter cells, and are the center of the organization of the cytoskeleton. Part of the spindle threads is attached to the chromosomes. In the cells of higher plants, the cell center does not have centrioles.

Centrioles are self-reproducing organelles of the cytoplasm. They arise as a result of duplication of existing ones. This happens when the centrioles diverge. The immature centriole contains 9 single microtubules; apparently, each microtubule is a template for the assembly of triplets characteristic of a mature centriole.

These are hair-like formations about 0.25 microns thick, built of microtubules, in eukaryotes they are covered with cilia only in length.

Cilia and flagella are the organelles of the movement of cells of many types. Most often, cilia and flagella are found in bacteria, some protozoa, zoospores and spermatozoa. Bacterial flagella have a different structure than eukaryotic flagella.

Cilia and flagella are formed by nine double microtubules that form the wall of a cylinder covered with a membrane; in its center are two single microtubules. This 9+2 type structure is characteristic of the cilia and flagella of almost all eukaryotic organisms, from protozoa to humans.

Cilia and flagella are reinforced in the cytoplasm by basal bodies that lie at the base of these organelles. Each basal body consists of nine triplets of microtubules; there are no microtubules in its center.

Microfilaments are represented by threads with a diameter of 6 nm, consisting of actin protein, close to muscle actin. Actin makes up 10-15% of the total amount of cell protein. In most animal cells, a dense network of actin filaments and their associated proteins forms under the plasma membrane itself. This network gives the surface layer of the cell mechanical strength and allows the cell to change its shape and move.

In addition to actin, myosin filaments are also found in the cell. However, their number is much less. Due to the interaction of actin and myosin, muscle contraction occurs.

Microfilaments are associated with the movement of the entire cell or its individual structures within it. In some cases, movement is provided only by actin filaments, in others, by actin together with myosin.

Inclusions are temporary components of the cytoplasm, sometimes appearing, sometimes disappearing. As a rule, they are contained in cells at certain stages of the life cycle. The specificity of inclusions depends on the specificity of the corresponding cells of tissues and organs. Inclusions are found predominantly in plant cells. They can occur in the hyaloplasm, various organelles, less often in the cell wall.

Functionally, inclusions are:

These are the most common plant cell inclusions. Starch is stored in plants exclusively in the form of starch grains.

They are formed only in the plastid stroma of living cells. During photosynthesis, green leaves produce assimilation, or primary starch. Assimilation starch does not accumulate in the leaves and, rapidly hydrolyzing to sugars, flows into the parts of the plant in which it accumulates. There it turns back into starch, which is called secondary. Secondary starch is also formed directly in tubers, rhizomes, seeds, that is, where it is deposited in stock. Then they call him spare. Leukoplasts that store starch are called amyloplasts.

Especially rich in starch are seeds, underground shoots (tubers, bulbs, rhizomes), parenchyma of conductive tissues of roots and stems of woody plants.

Found in almost all plant cells. The seeds and fruits are richest in them. Fatty oils in the form of lipid droplets are the second most important (after starch) form of reserve nutrients. Seeds of some plants (sunflower, cotton, etc.) can accumulate up to 40% of oil by weight of dry matter.

Lipid drops, as a rule, accumulate directly in the hyaloplasm. They are spherical bodies usually of submicroscopic size.

Lipid droplets can also accumulate in leukoplasts, which are called elaioplasts.

Protein inclusions are formed in various cell organelles in the form of amorphous or crystalline deposits of various shapes and structures. Most often, crystals can be found in the nucleus - in the nucleoplasm, sometimes in the perinuclear space, less often in the hyaloplasm, plastid stroma, in the extensions of the EPR tanks, the matrix of peroxisomes and mitochondria. Vacuoles contain both crystalline and amorphous protein inclusions. The largest number of protein crystals are found in the storage cells of dry seeds in the form of the so-called aleuronicgrains or protein bodies.

Storage proteins are synthesized by ribosomes during seed development and deposited in vacuoles. When the seeds ripen, accompanied by their dehydration, the protein vacuoles dry out and the protein crystallizes. As a result, in a mature dry seed, protein vacuoles turn into protein bodies (aleurone grains).

Inclusions formed in vacuoles, as a rule, cells of leaves or bark. These are either single crystals or groups of crystals of various shapes.

They are the end products of the vital activity of cells, which are formed as a device for removing excess calcium from the metabolism.

In addition to calcium oxalate, calcium carbonate and silica crystals can accumulate in cells.

Core

The most important component of eukaryotic cells. A nuclear-free cell does not exist for a long time. The nucleus is also incapable of independent existence.

Most cells have a single nucleus, but there are also multinucleated cells (in a number of protozoa, in the skeletal muscles of vertebrates). The number of cores can reach several tens. Some highly specialized cells lose their nucleus (mammalian erythrocytes and sieve tube cells in angiosperms).

The shape and size of cell nuclei are varied. Typically, the core has a diameter of 3 to 10 µm. The form is in most cases associated with the form

cells, but often differs from it. As a rule, it has a spherical or oval shape, less often it can be segmented, fusiform.

The main functions of the kernel are:

The core includes (Fig. 289):

The nucleus is delimited from the rest of the cytoplasm by a nuclear membrane consisting of two membranes of a typical structure. Between the membranes there is a narrow gap filled with a semi-liquid substance, - perinuclear space. In some places, both membranes merge with each other, forming nuclear pores through which the exchange of substances takes place between the nucleus and the cytoplasm. From the nucleus to the cytoplasm and back, substances can also enter due to the detachment of protrusions and outgrowths of the nuclear membrane.

Despite the active metabolism, the nuclear membrane provides differences in the chemical composition of nuclear juice and cytoplasm, which is necessary for the normal functioning of nuclear structures. The outer nuclear membrane from the side facing the cytoplasm is covered with ribosomes, giving it a roughness, the inner membrane is smooth. The nuclear envelope is part of the cell membrane system. Outgrowths of the outer nuclear membrane are connected to the channels of the endoplasmic reticulum, forming a single system of communicating channels.

Karyoplasm- internal contents of the kernel. It is a gel-like matrix in which chromatin and one or more nucleoli are located. The composition of nuclear juice includes various proteins (including nuclear enzymes), free nucleotides, as well as waste products of the nucleolus and chromatin.

The third structure characteristic of the cell nucleus is nucleolus, which is a rounded dense body immersed in nuclear juice. The number of nucleoli depends on the functional state of the nucleus and can vary from 1 to 5–7 or more (even in the same cell). Nucleoli are found only in non-dividing nuclei; during mitosis, they disappear, and after division is completed, they reappear. The nucleolus is not an independent structure of the nucleus. It is formed as a result of the concentration in a certain area of the karyoplasm of chromosome sections that carry information about the structure of rRNA. These sections of chromosomes are called nucleolar organizers. They contain numerous copies of the genes encoding rRNA. Since the process of rRNA synthesis and the formation of ribosome subunits is intensively going on in the nucleolus, we can say that the nucleolus is an accumulation of rRNA and ribosomes at different stages of formation.

chromatin called lumps, granules and network-like structures of the nucleus, intensely stained with some dyes and differing in shape from the nucleolus. Chromatin is a DNA molecule associated with proteins - histones. Depending on the degree of spiralization, there are:

Chromatin is a form of existence of genetic material in non-dividing cells and provides the possibility of doubling and realizing the information contained in it.

During cell division, DNA coils and chromatin structures form chromosomes.

Chromosomes called constant components of the cell nucleus, having a special organization, functional and morphological specificity, capable of self-reproduction and preservation of properties throughout ontogenesis. Chromosomes are dense, intensely staining structures (hence their name). They were first discovered by Fleming (1882) and Strassburger (1884). The term "chromosome" was coined by Waldeyer in 1888.

Functions of chromosomes:

The main chemical components of chromosomes are DNA (40%) and proteins (60%). The main component of chromosomes is DNA, since hereditary information is encoded in its molecules, while proteins perform structural and regulatory functions.

There are two main forms of chromosomes associated with certain phases and periods of the mitotic cycle:

Reorganization of chromosomes occurs in the process of spiralization (condensation) or despiralization (decondensation). In non-dividing cells, the chromosomes are in a decondensed state, since only in this case can the information embedded in them be read. During cell division, spiralization achieves dense packing of hereditary material, which is important for the movement of chromosomes during mitosis. The total length of the DNA of a human cell is 2 meters, while the total length of all the chromosomes of the cell is only 150 microns.

All information about chromosomes was obtained from the study of metaphase chromosomes. Each metaphase chromosome has two chromatids, which are daughter chromosomes (Fig. 290). They separate during mitosis. into daughter cells and become independent chromosomes. Chromatids- highly spiralized identical DNA molecules, forming

resulting from replication. They are connected to each other in the region of the primary constriction ( centromeres), to which the fission spindle threads are attached. The fragments into which the primary constriction divides the chromosome are called shoulders, and the ends of the chromosome - telomeres. Telomeres protect the ends of chromosomes from sticking together, thereby contributing to the preservation of chromosome integrity. Depending on the location of the centromere, they are distinguished (Fig. 291):

Some chromosomes have secondary constrictions arising in areas of incomplete condensation of chromatin. They are nucleolar organizers. Sometimes the secondary constriction is very long and separates a small section from the main body of the chromosome - satellite. Such chromosomes are called satellite.

Chromosomes have individual characteristics: length, position of the centromere, shape.

Each species of living organisms has a certain and constant number of chromosomes in its cells. The chromosomes of the nucleus of one cell are always paired. Each pair is formed by chromosomes that have the same size, shape, position of the primary and secondary constrictions. Such chromosomes are called homologous. Humans have 23 pairs of homologous chromosomes. The totality of quantitative (number and size) and qualitative (shape) features of the chromosome set of a somatic cell is called karyotype. The number of chromosomes in the karyotype is always even, since somatic cells have two chromosomes of the same shape and size: one is paternal, the other is maternal. The chromosome set is always species-specific, that is, it is characteristic only for a given type of organism. If in the nuclei of cells the chromosomes form homologous pairs, then such a set of chromosomes is called diploid(double) and denote - 2n. The amount of DNA corresponding to the diploid set of chromosomes is denoted as 2c. The diploid set of chromosomes is characteristic of somatic cells. In the nuclei of germ cells, each chromosome is represented in the singular. This set of chromosomes is called haploid(single) and denote - n. In humans, the diploid set contains 46 chromosomes, and the haploid set contains 23.

Together with membrane and non-membrane organelles in the cytoplasm, there are cell inclusions, which are non-permanent elements of the cell. They appear and disappear throughout its life cycle.

What refers to cellular inclusions, what is their role in the cell?

In fact, inclusions are metabolic products that can accumulate in the form of granules, grains or droplets with different chemical structures. Rarely found in the nucleus.

They are formed mainly in the lamellar complex and in the endoplasmic reticulum. Some are the result of incomplete digestion (hemosiderin).

The process of splitting and removal depends on the origin. Secretory inclusions are excreted through the ducts, carbohydrate and lipid inclusions are split under the action of enzymes, melanin is destroyed by Langerhans cells.

Classification of cellular inclusions:

Trophic (starch, glycogen, lipids);
secretory (inclusions of the pancreas, endocrine organs);
excretory (granules of uric acid);
pigment (melanin, bilirubin);
random (medicines, silicon);
mineral (calcium salts).

Structure and functions

fatty inclusions often accumulate in the cytoplasm as small droplets. They are characteristic of unicellular, for example, ciliates. In higher animals, lipid droplets are located in adipose tissue. Excessive accumulation of fatty inclusions leads to pathological changes in organs, for example, causes fatty degeneration of the liver.

Polysaccharides have a granular structure of various shapes and sizes. Their largest accumulations are located in the cells of the striated muscles and liver tissue.

Protein inclusions are not common, they are mainly a nutrient in the eggs (under microscopic examination, you can see all sorts of plates, sticks).

Pigment lipofuscin - these are inclusions of yellow or brown color that accumulate in cells during life. The pigment hemoglobin is part of the red blood cells. Rhodopsin - makes the rods of the retina sensitive to light.

Structure and functions of cellular inclusions
Group	Characteristic
Trophic	This includes proteins, fats and carbohydrates. Glycogen is found in animal cells, especially in the liver and muscle fibers. With loads and consumption of a large amount of energy, it is used in the first place. Plants store starch as their main source of nutrition.
excretory	These are the products of cell metabolism that have not been removed from it. This also includes foreign agents that have penetrated into the intracellular space. Such inclusions are absorbed and processed by lysosomes.
Secretory	Their synthesis takes place in special cells, and then they are brought out through the ducts or with the flow of lymph and blood. The secretory group includes hormones.
Pigment	Sometimes they are represented by metabolic products: lipofuscin granules or accumulations of hemosiderin. Found in melanocytes, color-coded cells. They perform a protective function, preventing the action of sunlight. In the simplest species, melanocytes are found in many organs, which gives animals a different color. In humans, the main mass of pigment cells is located in the epidermis, part in the iris of the eye.
Random	Found in cells capable of phagocytosis. Captured bacteria that are poorly digested remain in the cytoplasm as granules.
mineral	These include Ca salts, which are deposited with a decrease in the activity of the organ. Violation of ion metabolism also leads to the accumulation of salts in the mitochondrial matrix.

Biological and medical significance of cellular inclusions

Excessive accumulation of inclusions can lead to the development of serious pathologies, which are commonly called accumulation diseases. The formation of the disease is associated with a decrease in the activity of lysosomal enzymes and excessive intake of any substances (fatty degeneration of the liver, glycogen muscle tissue).

For example, the development of hereditary Pompe disease is due to a deficiency of the enzyme acid maltase, as a result, glycogen is heated in the cells, which leads to dystrophy of the nervous and muscle tissue.

Substances characteristic of the cell, as well as foreign substances that do not normally occur (amyloidosis of the kidneys) can accumulate in the cytoplasm. During the aging of the body, lipofuscin accumulates in all cells, which serves as a marker of the functional inferiority of cells.

How do organelles differ from cellular inclusions?

Organelles - these are permanent structural elements of the cell, necessary for stable work and life.

Inclusions - these are the components of a cell that can come and go throughout its lifetime.

Organelles are specialized sections of the cytoplasm of a cell that have a specific structure and perform specific functions in the cell. They are divided into general-purpose organelles that are found in most cells (mitochondria, the Golgi complex, endoplasmic reticulum, ribosomes, cell center, lysosomes, plastids and vacuoles), and special-purpose organelles that are found only in specialized cells (myofibrils - in muscle cells , flagella, cilia, pulsating vacuoles - in protozoan cells). Most organelles have a membrane structure. Membranes are absent in the structure of ribosomes and the cell center. The cell is covered with a membrane, which consists of several layers of molecules,

providing selective permeability of substances. in the cytoplasm

the smallest structures are located - organelles. to cell organelles

include: endoplasmic reticulum, ribosomes, mitochondria, lysosomes,

Golgi complex, cell center.

The cytoplasm contains a number of tiny cell structures - organelles,

which perform different functions. Organelles provide

cell viability.

Endoplasmic reticulum.

The name of this organoid reflects its location in

the central part of the cytoplasm (Greek "endon" - inside). EPS presents

a very branched system of tubules, tubules, vesicles, cisterns

different sizes and shapes, delimited by membranes from the cytoplasm of the cell.

EPS is of two types: granular, consisting of tubules and cisterns,

the surface of which is dotted with grains (granules) and agranular, i.e.

smooth (no grains). The granules in the endoplasmic reticulum are nothing but

ribosomes. Interestingly, in the cells of animal embryos, it is observed in

mainly granular EPS, and in adult forms - agranular. Knowing that

ribosomes in the cytoplasm serve as a site for protein synthesis, it can be assumed that

granular ER predominates in cells actively synthesizing protein.

It is believed that the agranular network is more provided in those

cells where there is an active synthesis of lipids (fats and fat-like substances).

Both types of endoplasmic reticulum are not only involved in the synthesis

organic substances, but also accumulate and transport them to places

purpose, regulate the metabolism between the cell and its environment.

Ribosomes.

Ribosomes are non-membrane cellular organelles composed of

ribonucleic acid and protein. Their internal structure is much more

remains a mystery. In an electron microscope, they look like rounded or

mushroom granules.

Each ribosome is divided by a groove into large and small parts.

(subunits). Often several ribosomes are connected by a special thread

ribonucleic acid (RNA), called informational (i-RNA). Ribosomes

perform a unique function of synthesizing protein molecules from amino acids.

Golgi complex.

Biosynthesis products enter the lumen of the cavities and tubules of the EPS,

where they are concentrated into a special apparatus - the Golgi complex,

located near the nucleus. The Golgi complex is involved in transport

biosynthetic products to the cell surface and in their removal from the cell, in

formation of lysosomes, etc.

The Golgi complex was discovered by the Italian cytologist Camilio Golgi

and in 1898 was called the "complex (apparatus) of the Golgi".

Proteins produced in ribosomes enter the Golgi complex, and when they

are required by another organoid, then part of the Golgi complex is separated, and the protein

delivered to the desired location.

Lysosomes.

Lysosomes (from the Greek "Lizeo" - I dissolve and "Soma" - the body) are

oval-shaped cell organelles surrounded by a single-layer membrane. In them

there is a set of enzymes that destroy proteins, carbohydrates, lipids. AT

If the lysosomal membrane is damaged, enzymes begin to break down and

destroy the internal contents of the cell, and it dies.

Cell center.

The cell center can be observed in cells capable of dividing. He

consists of two rod-shaped bodies - centrioles. near the core and

Golgi complex, the cell center is involved in the process of cell division, in

spindle formation.

energy organelles.

Mitochondria(Greek "mitos" - thread, "chondrion" - granule) is called

powerhouses of the cell. This name stems from the fact that

it is in the mitochondria that the extraction of energy contained in

nutrients. The shape of mitochondria is variable, but most often they have

type of threads or granules. Their size and number are also unstable and depend on

functional activity of the cell.

Electron micrographs show that mitochondria are composed of

two membranes: outer and inner. The inner membrane forms outgrowths,

called cristae, which are completely covered with enzymes. Presence of cristae

increases the total surface of mitochondria, which is important for active

enzyme activity.

Mitochondria have their own specific DNA and ribosomes. Due

with this, they self-reproduce during cell division.

Chloroplasts- shaped like a disk or a ball with a double shell -

external and internal. The chloroplast also contains DNA, ribosomes and

special membrane structures - grains interconnected and internal

chloroplast membrane. The gran membranes contain chlorophyll. Thanks to

chlorophyll in chloroplasts converts the energy of sunlight into

chemical energy of ATP (adenosine triphosphate). The energy of ATP is used in

chloroplasts to synthesize carbohydrates from carbon dioxide and water.

Cellularinclusion are non-permanent structures of the cell. These include drops and grains of proteins, carbohydrates and fats, as well as crystalline inclusions (organic crystals that can form proteins, viruses, oxalic acid salts, etc. in cells, and inorganic crystals formed by calcium salts). Unlike organoids, these inclusions do not have membranes or cyoskeletal elements and are periodically synthesized and consumed. Drops of fat are used as a reserve substance due to its high energy content. Grains of carbohydrates (polysaccharides; in the form of starch in plants and in the form of glycogen in animals and fungi - as an energy source for the formation of ATP; protein grains - as a source of building material, calcium salts - to ensure the process of excitation, metabolism, etc.)