Cellular center: functions and structure, distribution of genetic information. Cytoplasmic inclusions

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

Basic characteristics of eukaryotes.

1. The cell is divided into cytoplasm and nucleus.
2. 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.
3. Nuclear DNA is divided into strands that are not closed in rings.
4. DNA strands are linearly elongated within chromosomes and are clearly visible during mitosis. The set of chromosomes in the nuclei of somatic cells is diploid.
5. A system of external and internal membranes has been developed. The internal ones divide the cell into separate compartments - compartments. Take part in the formation of cell organelles.
6. 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.
7. A large number of organelles are limited by a single membrane (lysosomes, vacuoles, etc.)
8. In a eukaryotic cell, organelles of general and special importance are distinguished. For example: general meaning – nucleus, mitochondria, EPS, etc.; of special significance are microvilli of the absorptive surface of the intestinal epithelial cell, cilia of the epithelium of the trachea and bronchi.
9. Mitosis is a characteristic mechanism of reproduction in generations of genetically similar cells.
10. Characteristic of the sexual process. True sex cells - gametes - are formed.
11. Not capable of fixing free nitrogen.
12. Aerobic respiration occurs in mitochondria.
13. Photosynthesis takes place in chloroplasts containing membranes, which are usually arranged in grana.
14. Eukaryotes are represented by unicellular, filamentous and truly multicellular forms.

Main structural components of a eukaryotic cell

organoids

Core. Structure and functions.

A cell has a nucleus and cytoplasm. Cell nucleus consists of a membrane, nuclear juice, nucleolus and chromatin. Functional role nuclear envelope consists in the isolation of the genetic material (chromosomes) of a 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 space. The latter can communicate with the tubules of the cytoplasmic reticulum.

The nuclear envelope is penetrated by a pore with a diameter of 80-90 nm. The pore region or pore complex with a diameter of about 120 nm has a certain structure, which indicates a complex mechanism for regulating the 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 membrane. In mature erythrocytes of these animals, which retain their nuclei, up to five pores remain per 1 μg of membrane, i.e. 6 times less.

In the area of ​​the feather complex the so-called dense plate - the protein layer underlying the entire inner membrane of the nuclear envelope. 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 lamina promotes the ordered arrangement of chromosomes in the interphase nucleus.

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

Nucleolus represents the structure in which formation and maturation occurs ribosomal RNA (rRNA). rRNA genes occupy certain sections (depending on the type of animal) of one or several chromosomes (in humans there are 13-15 and 21-22 pairs) - nucleolar organizers, in the area of ​​which nucleoli are formed. Such areas in metaphase chromosomes look like narrowings and are called secondary constrictions. WITH Using an electron microscope, filamentous and granular components are identified 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. During the process of maturation, fibrils are transformed into ribonucleoprotein grains (granules), which represent the granular component.

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

cytoplasm

IN cytoplasm distinguish between the main substance (matrix, hyaloplasm), inclusions and organelles. Basic substance of the cytoplasm fills the space between the plasmalemma, nuclear envelope and other intracellular structures. An ordinary electron microscope does not reveal any internal organization in it. The protein composition of hyaloplasm is diverse. The most important proteins are represented by enzymes of glycolysis, 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 performance of a unifying and scaffolding function by the matrix may be associated with a microtrabecular network, detected using a high-power electron microscope, formed by thin fibrils 2-3 nm thick and penetrating the entire cytoplasm. A significant amount of intracellular movement of substances and structures occurs through the hyaloplasm. The main substance of the cytoplasm should be considered in the same way as a complex colloidal system capable of transitioning from a sol-like (liquid) state to a gel-like state. In the process of such transitions, work is done. For the functional significance of such transitions, see Section. 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 (secretion granules), and ballast substances (some pigments).

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

Organelles are isolated general meaning And special. The latter are present in significant quantities in cells specialized to perform a specific function, but in small quantities they can also be found in other types of cells. These include, for example, microvilli of the absorptive surface of the intestinal epithelial cell, cilia of the epithelium of the trachea and bronchi, synaptic vesicles, transporting substances that carry nervous excitation from one nerve cell to another or a cell of the working organ, myofibrils on which muscle contraction depends. A detailed examination of special organelles is part of the histology course.

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. Plant cells also contain chloroplasts, in which photosynthesis occurs.

Kanaltsevaya And vacuolar system formed by communicating or separate tubular or flattened (cistern) cavities, bounded by membranes and spreading throughout the cytoplasm of the cell. Often tanks have bubble-like expansions. In the named system there are rough And smooth cytoplasmic reticulum(see Fig. 2.3). A structural feature of the rough network is the attachment of polysomes to its membranes. Because of this, it performs the function of synthesizing a certain category of proteins that are predominantly 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 occurs, as well as their assembly. The cisterns of the rough network, densely packed in a layered structure, are the sites of the most active protein synthesis and are called ergastoplasma.

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, in particular material secreted by the glandular cell, move from the site of synthesis to the zone of packaging into granules. In areas of liver cells rich in smooth network structures, harmful toxic substances and some drugs (barbiturates) are destroyed and neutralized. 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 round ribonucleoprotein particle with a diameter of 20-30 nm. It consists of small and large subunits, the combination of which occurs in the presence of messenger RNA (mRNA). One molecule of mRNA usually links several ribosomes together like a string of beads. This structure is called polysome. Polysomes are freely located in the main substance of the cytoplasm or attached to the membranes of the rough cytoplasmic reticulum. In both cases, they serve as a site of 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, led to the conclusion that proteins are formed on hyaloplasma polysomes for their own needs (for “home” use) of a given 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 in number from several tens (usually about 20) to several hundreds and even thousands per cell.

Dictyosome(Fig. 2.6, A) is represented by a stack of 3-12 flattened disc-shaped cisterns, from the edges of which vesicles (vesicles) are laced. Limited to a certain area (local) expansion of the cisterns gives rise to larger vesicles (vacuoles). In differentiated cells of vertebrates and humans, dictyosomes are usually collected 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 that must be removed from the cell. In this case, the precursor of the secretion (prosecret), entering the dictyosome from the synthesis zone, undergoes some chemical transformations in it. It is also isolated (segregated) in the form of “portions”, which are also covered with a membrane shell. Lysosomes are formed in the lamellar complex. Dictyosomes synthesize polysaccharides, as well as their complexes with proteins (glycoproteins) and fats (glycolipids), which can then be found in the glycocalyx of the cell membrane.

The mitochondrial shell consists of two membranes that differ in chemical composition, set of enzymes and functions. The inner membrane forms leaf-shaped (cristae) or tubular (tubules) invaginations. 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 the organelle's own protein biosynthesis apparatus. It is represented by 2 copies of a circular DNA molecule devoid of histones (as in prokaryotes), ribosomes, a set of transfer RNAs (tRNAs), enzymes for DNA replication, transcription and translation of hereditary information. In terms of its basic 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 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 storing energy in a biologically usable form (by synthesizing adenosine triphosphate -ATP molecules). In general this process is called oxidative(disbandment. Matrix components and the inner membrane actively participate in the energy function of mitochondria. It is with this membrane that the electron transport chain (oxidation) and ATP synthetase, which catalyzes the oxidation-associated phosphorylation of ADP into ATP, are associated. Among the side functions of mitochondria is participation in the synthesis of steroid hormones and some amino acids (glutamic).

Lysosomes(Fig. 2.6, IN) 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 environment) breakdown of nucleic acids, proteins, fats, and polysaccharides at low pH values. Their shell is formed by a single membrane, sometimes covered on the outside with a fibrous protein layer (in electron diffraction patterns there are “bordered” bubbles). The function of lysosomes is the intracellular digestion of various chemical compounds and structures.

Primary lysosomes(diameter 100 nm) are called inactive organelles, secondary - organelles in which the digestion process occurs. Secondary lysosomes are formed from primary ones. They are divided into heterolysosomes(phagolysosomes) and autolysosomes(cytolysosomes). Firstly (Fig. 2.6, G) material entering the cell from the outside is digested through pinocytosis and phagocytosis, and secondly, the cell’s own structures, which have completed their function, are destroyed. Secondary lysosomes, in which the digestion process is completed, are called residual bodies(telolysosomes). They lack hydrolases and contain undigested material.

Microbodies form a collective 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 involved in various metabolic cycles, for example in the exchange of uric acid in liver and kidney cells. In a liver cell, the number of peroxisomes reaches 70-100.

Organelles of general importance also include some permanent structures of the cytoplasm that lack 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 a free state in the cytoplasm of cells or as structural elements of flagella, cilia, mitotic spindles, and centrioles. Free microtubules and microtubules of cilia, flagella and centrioles have different resistance to destructive influences, for example chemical (colchicine). Microtubules are built from stereotypical protein subunits through their polymerization. In a living cell, polymerization processes occur simultaneously with depolymerization processes. The ratio of these processes determines the number of microtubules. In a free state, microtubules perform a supporting function, determining the shape of cells, and are also factors in the directional movement of intracellular components.

Microfilaments(Fig. 2.6, E) are called long, thin structures, 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, amoeboid. They are also credited with a scaffolding role and participation in the organization of intracellular movements of organelles and areas 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 filstents. In epithelial, nerve, glial, muscle cells, fibroblasts, they are built from different proteins. Intermediate filaments apparently perform a mechanical, scaffolding function.

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

Characteristic for animal cells, parts of plant cells, fungi and algae cell center, which contains centrioles. Centriole(under an electron microscope) has the appearance of 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 includes the formation of mitotic spindle threads, which are also formed by microtubules. Centrioles polarize the process of cell division, ensuring the separation of sister chromatids (chromosomes) in anaphase of mitosis.

A eukaryotic cell has a cellular skeleton (cytoskeleton) of intracellular fibers (Rings) - early 20th century, rediscovered at the end of 1970. This structure allows the cell to have its own shape, sometimes changing it. Cytoplasm is in motion. The cytoskeleton is involved in the process of organelle transfer and participates in cell regeneration.

Mitochondria are complex formations with a double membrane (0.2-0.7 µm) and different shapes. The inner membrane has cristae. The outer membrane is permeable to almost all chemicals, 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 ribosome system, a DNA molecule. Mutations may occur (more than 66 diseases). As a rule, they are associated with insufficient ATP energy and are often associated with cardiovascular failure and pathologies. The number of mitochondria is different (there is 1 mitochondria in a trypanosome cell). The amount depends on age, function, tissue activity (liver - more than 1000).

Lysosomes are bodies surrounded by an elementary membrane. Contains 60 enzymes (40 lysosomal, hydrolytic). Inside the lysosome there is a neutral environment. They are activated by low pH values, entering the cytoplasm (self-digestion). Lysosome membranes protect the cytoplasm and cell from destruction. They are formed in the Golgi complex (intracellular stomach; they can recycle spent cell structures). There are 4 types. 1-primary, 2-4 – secondary. Through endocytosis, a substance enters the cell. The primary lysosome (storage granule) with a set of enzymes absorbs the substance and a digestive vacuole is formed (with complete digestion, breakdown occurs 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. Autophagy lysosomes destroy the cell's own structures (unnecessary structures). May contain mitochondria, parts of the Golgi complex. Often formed during fasting. May occur when exposed to other cells (red blood cells).

Divides all cells (or alive organisms) into two types: prokaryotes And eukaryotes. Prokaryotes are nuclear-free cells or organisms, which include viruses, prokaryotic bacteria and blue-green algae, in which the cell consists directly of the cytoplasm, in which one chromosome is located - DNA molecule(sometimes RNA).

Eukaryotic cells have a core containing nucleoproteins (histone protein + DNA complex), as well as others organoids. Eukaryotes include the majority of modern unicellular and multicellular living organisms known to science (including plants).

The structure of eukaryotic granoids.

Cell nucleus is the main and most complex organelle of the cell, so we will consider it

Cytoplasm is the internal contents of the cell and consists of hyaloplasm and various intracellular structures located in it.

Hyaloplasma(matrix) is an aqueous solution of inorganic and organic substances that can change their viscosity and are in constant motion. The ability to move or flow the cytoplasm is called cyclosis.

The matrix is ​​an active environment in which many physical and chemical processes take place and which unites all the elements of the cell into a single system.

The cytoplasmic structures of the cell are represented by inclusions and organelles. Inclusions- relatively unstable, found in certain types of cells at certain moments of life, for example, as a reserve of nutrients (starch grains, proteins, glycogen drops) or products to be released from the cell. Organoids - permanent and essential components of most cells, having a specific structure and performing a vital function.

TO membrane organelles Eukaryotic cells include the endoplasmic reticulum, Golgi apparatus, mitochondria, lysosomes, and plastids.

Endoplasmic reticulum. The entire internal zone of the cytoplasm is filled with numerous small channels and cavities, the walls of which are membranes similar in structure to the plasma membrane. These channels branch, connect with each other and form a network called the endoplasmic reticulum.

The endoplasmic reticulum is heterogeneous in its structure. There are two known types of it - granular and smooth. On the membranes of the channels and cavities of the granular network there are many small round bodies - ribosomes, which give the membranes a rough appearance. The membranes of the smooth endoplasmic reticulum do not carry ribosomes on their surface.

The endoplasmic reticulum performs many diverse functions. The main function of the granular endoplasmic reticulum is participation in protein synthesis, which occurs in ribosomes.

The synthesis of lipids and carbohydrates occurs on the membranes of the smooth endoplasmic reticulum. All these synthesis products accumulate in channels and cavities, and are then transported to various organelles of the cell, where they are consumed or accumulated in the cytoplasm as cellular inclusions. The endoplasmic reticulum connects the main organelles of the cell.

Golgi apparatus ( see Fig.4). In many animal cells, such as nerve cells, it takes the form of a complex network located around the nucleus. In the cells of plants and protozoa, the Golgi apparatus is represented by individual sickle- or rod-shaped bodies. The structure of this organelle is similar in the cells of plant and animal organisms, despite the diversity of its shape.

The Golgi apparatus includes: cavities bounded by membranes and located in groups (5-10); large and small bubbles located at the ends of the cavities. All these elements form a single complex.

The Golgi apparatus performs many important functions. The products of the cell's synthetic activity - proteins, carbohydrates and fats - are transported to it through the channels of the endoplasmic reticulum. All these substances first accumulate, and then, in the form of large and small bubbles, enter the cytoplasm and are either used in the cell itself during its life, or removed from it and used in the body. For example, in the cells of the mammalian pancreas, digestive enzymes are synthesized, which accumulate in the cavities of the organelle. Bubbles filled with enzymes then form. They are excreted from the cells into the pancreatic duct, from where they flow into the intestinal cavity. Another important function of this organelle is that on its membranes the synthesis of fats and carbohydrates (polysaccharides) occurs, which are used in the cell and which are part of the membranes. Thanks to the activity of the Golgi apparatus, renewal and growth of the plasma membrane occurs.

Mitochondria. The cytoplasm of most animal and plant cells contains small bodies (0.2-7 microns) - mitochondria (Greek "mitos" - thread, "chondrion" - grain, granule).

Mitochondria are clearly visible in a light microscope, with which you can examine their shape, location, and count their number. The internal structure of mitochondria was studied using an electron microscope. The mitochondrial shell consists of two membranes - outer and inner. The outer membrane is smooth, it does not form any folds or outgrowths. The inner membrane, on the contrary, forms numerous folds that are directed into the mitochondrial cavity. The folds of the inner membrane are called cristae (Latin “crista” - ridge, outgrowth). The number of cristae varies in the mitochondria of different cells. There can be from several tens to several hundred of them, with especially many cristae in the mitochondria of actively functioning cells, such as muscle cells.

Mitochondria are called the “power stations” of cells because their main function is the synthesis of adenosine triphosphoric acid (ATP). This acid is synthesized in the mitochondria of the cells of all organisms and is a universal source of energy necessary for the vital processes of the cell and the whole organism.

New mitochondria are formed by the division of mitochondria already existing in the cell.

Lysosomes. They are small round bodies. Each lysosome is separated from the cytoplasm by a membrane. Inside the lysosome there are enzymes that break down proteins, fats, carbohydrates, and nucleic acids.

Lysosomes approach a food particle that has entered the cytoplasm, merge with it, and one digestive vacuole is formed, inside which there is a food particle surrounded by lysosome enzymes. Substances formed as a result of the digestion of food particles enter the cytoplasm and are used by the cell.

Possessing the ability to actively digest nutrients, lysosomes participate in the removal of cell parts, whole cells and organs that die during vital activity. The formation of new lysosomes occurs constantly in the cell. Enzymes contained in lysosomes, like any other proteins, are synthesized on ribosomes in the cytoplasm. These enzymes then travel through the endoplasmic reticulum to the Golgi apparatus, in the cavities of which lysosomes are formed. In this form, lysosomes enter the cytoplasm.

Plastids. Plastids are found in the cytoplasm of all plant cells. There are no plastids in animal cells. There are three main types of plastids: green - chloroplasts; red, orange and yellow - chromoplasts; colorless - leucoplasts.

Mandatory for most cells are also organelles that do not have a membrane structure. These include ribosomes, microfilaments, microtubules, and the cell center.

Ribosomes. Ribosomes are found in the cells of all organisms. These are microscopic round bodies with a diameter of 15-20 nm. Each ribosome consists of two particles of unequal size, small and large.

One cell contains many thousands of ribosomes; they are located either on the membranes of the granular endoplasmic reticulum or lie freely in the cytoplasm. Ribosomes contain proteins and RNA. The function of ribosomes is protein synthesis. Protein synthesis is a complex process that is carried out not by one ribosome, but by a whole group, including up to several dozen united ribosomes. This group of ribosomes is called a polysome. Synthesized proteins first accumulate in the channels and cavities of the endoplasmic reticulum and are then transported to organelles and cell sites where they are consumed. The endoplasmic reticulum and ribosomes located on its membranes represent a single apparatus for the biosynthesis and transport of proteins.

Microtubules and microfilaments - thread-like structures consisting of various contractile proteins and determining the motor functions of the cell. Microtubules look like hollow cylinders, the walls of which consist of proteins - tubulins. Microfilaments are very thin, long, thread-like structures composed of actin and myosin.

Microtubules and microfilaments permeate the entire cytoplasm of the cell, forming its cytoskeleton, causing cyclosis, intracellular movements of organelles, divergence of chromosomes during the division of nuclear material, etc.

Cellular center (centrosome) (see Fig. 3). In animal cells, near the nucleus there is an organelle called the cell center. The main part of the cell center consists of two small bodies - centrioles, located in a small area of ​​​​densified cytoplasm. Each centriole has the shape of a cylinder up to 1 µm long. Centrioles play an important role in cell division; they participate in the formation of the division spindle.

In the process of evolution, different cells adapted to living in different conditions and performing specific functions. This required the presence of special organelles in them, which are called specialized in contrast to the general purpose organoids discussed above. These include contractile vacuoles protozoa, myofibrils muscle fiber, neurofibrils And synaptic vesicles nerve cells microvilli epithelial cells, cilia And flagella some protozoa.

Inclusions- these are non-permanent (optional) structural elements of the cytoplasm.

They are visible under light microscopy using general staining methods, sometimes at low and medium magnification, and some of them can only be detected by special (histochemical, immunological) methods or by electron microscopy. Depending on the activity of the cell, hormonal and metabolic influences, differentiation characteristics, age, and the action of various environmental factors, a wide variety of inclusions in composition and quantity can be found in cells.

Inclusions indicate the characteristics of metabolism, differentiation, and functional activity of cells. Many inclusions appear during dystrophic disorders in the cell, which is accompanied by changes in its vital activity up to death. Sometimes the contents of inclusions are not only an indicator of function, but the basis for the name of the cell: pigment cells - melanocytes; eosinophilic, basophilic and neutrophilic blood granulocytes, etc.

With all the variety of inclusions, they can be combined according to their functional purpose.

Secretory inclusions. They are secretory granules that are released from the cell by exocytosis. According to their chemical composition, they are divided into protein (serous), fat (lipid, or liposomes), mucous (contain mucopolysaccharides), etc. The number of inclusions depends on the functional activity of the cell, the stage of the secretory cycle, and the degree of maturity of the cell. There are especially many granules in differentiated, functionally active cells during the accumulation phase of the secretory cycle.

Secretory inclusions are formed in the Golgi complex. Before this, they go through the stage of synthesis in gr. or smooth. EPS, less often this occurs in other structures.

Secretory protein inclusions are varied in size, distribution in the cytoplasm, and electron density. They are surrounded by a cell membrane. Polypeptide chains of the contents of secretory inclusions are synthesized in gr. EPS, and mature in the Golgi complex. In this regard, cells that synthesize secretory proteins have well-developed organelles, a large nucleus and nucleoli. However, if the cell stops the synthesis of inclusions, their accumulation is accompanied by involution of the cell. ER and Golgi complex.

In exocrine glands, secretory inclusions predominate in the apical part of the cell, suggesting secretion into the external environment. Secretory inclusions of the endocrine glands are concentrated near blood vessels or evenly distributed in the cytoplasm.

Mucous secretory inclusions are found mainly in the cells of the mucous secretory glands. An example of single-celled secretory glands is the goblet cells of the small intestine. With light microscopy using the PIR reaction, mucus is clearly visible in large vacuoles.

Secretory inclusions containing fats (liposomes) are present in the cytoplasm of the sebaceous glands and endocrine cells that synthesize steroid hormones (cholesterol derivatives). Steroid hormones are male and female sex hormones, stress hormones (glucocorticoids) and a hormone that controls the content of sodium ions in the body (aldosterone). In these cells smoothness and gr. are well developed. ER, Golgi complex, many mitochondria. Mitochondria of endocrinocytes are involved in the synthesis of steroid hormones and have specific structural features. These are large mitochondria with multivesicular (tubular) cristae.

Secretory inclusions containing derivatives of amino acids and other amines are also isolated: norepinephrine and adrenaline, serotonin (melatonin), etc.

The composition of secretory inclusions in a mast cell (mash) and basophilic granulocyte (basophil) is diverse. These cells contain numerous large secretory inclusions that are stained with basic dyes and often change their shade. This ability to change the color of the dye is called metachromasia. Electron microscopy shows that mast cells and granulocytes contain many large round granules of varying electron density.

The number of inclusions depends on the stage of the secretory cycle. Their number is maximum at the stage of secretion accumulation, but at other stages they may be absent or their concentration in the cell is minimal.

Trophic inclusions. These are structures in which cells and the body as a whole store nutrients necessary in conditions of energy deficiency, lack of structural molecules (during starvation). Examples of trophic inclusions are granules with glycogen (liver cells, muscle cells and symplasts), lipid inclusions in fat and other cells.

Trophic inclusions of glycogen are small, irregularly shaped granules that can be detected by electron microscopy, as well as by light microscopy using special staining methods. Glycogen, when broken down, turns into glucose, which is used by the cell and the body as a whole in conditions of its deficiency.

Lipid inclusions normally accumulate in adipose tissue (white or brown fat). In a white fat lipocyte, the inclusions merge into a giant drop that occupies the entire central part of the cell. Such cells acquire a round shape and large size. The nuclei are flattened and shifted to the periphery, there are few organelles. In brown fat lipocytes, inclusions do not merge into one drop, the nuclei lie centrally, there are many mitochondria, the Golgi complex and smooth are developed. EPS.

When switching to fat metabolism, the destruction of lipids in adipose tissue supports the body's energy needs. Lipid inclusions are more easily destroyed in brown fat than in white fat. Excessive accumulation of lipids in adipose tissue is called obesity.

Trophic lipid droplets can accumulate outside fat cells: in hepatocytes, skeletal and cardiac myocytes, renal tubular apparatus, etc. A large accumulation of such inclusions, which is reversible and does not disrupt cell function, is called fatty infiltration. When such accumulation leads to cell damage, this phenomenon is called fatty degeneration. Fatty degeneration of the artery wall - atherosclerosis.

Pigment inclusions. This type of inclusion imparts color to the cells; provides a protective function, for example, melanin granules in the pigment cells of the skin protect against sunburn. Pigment inclusions can consist of cell waste products: granules with lipofuscin in neurons, hemosiderin in macrophages.

Pigment cells - melanocytes in low-organized vertebrates are found in many organs, giving animals a variety of colors. The shape of the cells is also different, but mostly multi-processed.

In mammals and humans, melanocytes are found mainly in the epithelium. In multilayered epithelium, they lie in the basal layer, and their processes are directed to the spinous layer. The pigment of melanocyte inclusions, melanin, is a derivative of the amino acid tyrosine. Melanin accumulates in numerous inclusions located in the cell body and processes. Some of the inclusions are released and captured by neighboring cells. If cells are unable to produce melanin, this leads to albinism.

Excretory inclusions. These are inclusions of substances captured by the cell from the internal environment and excreted from the body: toxic substances, metabolic products, foreign structures. Excretory inclusions are often found in the epithelium of the kidney tubules, primarily in the proximal ones. The proximal tubules remove substances that the body does not need that cannot be filtered through the glomerular apparatus.

Random inclusions. Characteristic of phagocytes that capture structures foreign to the body (dust particles, bacteria and viruses), poorly digestible and indigestible macromolecular organic and inorganic complexes. Most often, such inclusions are found in specialized cells that carry out phagocytosis - neutrophil leukocytes and macrophages.

Mineral inclusions. These are mainly insoluble calcium salts (carbonates, phosphates). They are formed with reduced organ activity, hypotrophy and atrophy. Often mineral inclusions (calcium salts) are found in the mitochondrial matrix, this is due to the high content of this ion and changes in metabolism in the organelle.

Inclusions in pathology, can accumulate in excess quantities and lead to disruption of the structure and function of the cell (dystrophy). Dystrophy is caused by storage diseases associated with insufficient activity of lysosomes and/or excessive synthesis of any substances (fatty liver, neuronal degeneration, with the accumulation of a large number of granules with lipofuscin, glycogenosis of the liver and muscles, etc.). Both substances common to the cell (glycogen in hepatocytes) and substances not normally found in the cell (amyloid) can accumulate.

Most inclusions are separated from the cytoplasmic matrix by a membrane (secretory inclusions, fatty trophic inclusions, etc.). However, there are also inclusions that come into contact with the contents of the hyaloplasm (glycogen, some mineral inclusions).

The origin of inclusions is varied and depends on their content. For example, the bulk of secretory and trophic inclusions are formed in the Golgi complex or in the ER, and random inclusions, hemosiderin granules, are products of incomplete digestion and phagocytosis.

The utilization and removal of inclusions from the cell depend on the nature of the inclusion itself. Secretory inclusions are removed from the cell by exocytosis; glycogen and lipids are broken down by cell enzymes and released into the extracellular environment in the form of metabolic products (glucose, glycerol, fatty acids); melanin is secreted by a pigment cell, then it is captured and destroyed by a Langerhans cell.

Thus, the inclusions are structures of different origin, functional purpose and morphology. Their number and type can be indicators of the characteristics of differentiation and functional state of cells.

In contrast, inclusions are obligatory and permanent structural elements of the cytoplasm, having a certain structure, performing specific functions aimed at maintaining the vital activity of the entire system as a whole. Inclusions are mobile inclusions.

Classification of organelles

• 1. By prevalence
• A) general (mitochondria, EPS, Golgi complex, etc.)
• B) special (inherent in cells only of a certain type and caused by the performance of specific functions (tonofibrils - in the epithelium, contractile fibrils - in muscle fibers, neurofibrils - in the processes of nerve cells.
• 2. By structure
• A) Membrane organelles (lysosomes, peroxisomes, EPS, Golgi complex and mitochondria)
• B) Non-membrane organelles (Ribosomes, cell center, microtubules, intermediate filaments and microfilaments)
• 3. By function.
• A) Intracellular digestion apparatus (lysosomes and peroxisomes)
• B) Synthetic apparatus of the cell (ribosomes, EPS, Golgi complex)
• B) The energy apparatus of the cell (mitochondria)
• D) Cytoskeleton (microtubules, intermediate filaments and microfiloments)

Non-membrane organelles.

Ribosomes are a non-membrane organelle belonging to the synthetic apparatus of the cell, and have the appearance of small particles of 10-30 Nm.

Each ribosome consists of two subunits. Big and small. Having different molecular weights and in the non-catative state they are in a dissociated form. During the process of biosynthesis, subunits combine complementarily and carry out the biosynthesis of protein molecules. Ribosomes are made up of ribosomal RNA

Ribosomes can be found either in free or bound form. Ribosomes can group and form polysomes, bound or attached to the surface of the biological membrane, the granular endoplasmic reticulum.

Ribosomal subunits are formed in the nucleus in the region of nucleolar organizers; these are sections of chromosomes where secondary constrictions are located (chromosomes 13-14,15,21,22). After formation, the subunits leave the nucleus into the cytoplasm, complex and interact with messenger and transfer RNA. Messenger RNA indicates in which sequence the amino acids should be placed, based on the sequence of nucleotides in the chain of the DNA molecule. Messenger RNA is an exact copy of one of the strands. Transfer RNA performs a transport function, and ribosomal RNA arranges amino acids into the pilipeptide chain, and RNA synthesis occurs on free ribosomes.

Microtubules are key organelles of the cell skeleton and are part of the cytoskeleton. A lot of tubes are located in the cortical layer of the cytoplasm. The microtubule looks like a hollow cylinder about 20-25 nanometers in diameter. The inner part is filled with a substance with low electron density. It consists of the globular protein tubulin alpha and beta fractions, located in a checkerboard pattern and forming 13 spirally twisted protfeloments in the wall, located parallel to each other. Tubulin does not have AT-Phase activity, that is, it is not able to hydrolyze the ATP molecule and that is why microtubules are not capable of contraction. Tubulin has the ability to polymerize and depolymerize. Various physical and chemical factors can polymerize or depolymerize tubulin.

There are many substances that depolymerize tubulin. Since tubulin is part of the spindle filaments, and by influencing it with various factors, it is possible to either stop or enhance cell division. This is the basis of the action of antitumor drugs, which cause the breakdown of spindle microtubules and stop tumor growth. Functions of microtubules:

• 1. Support,
• 2. Promote changes in the shape and size of the cell,
• 3. Participate in transport processes and participate in the processes of intracellular movement of various organelles. It has been established that with the help of dynein proteins, organelles can be fixed to the tubes. And by changing the concentration of dynein, they can slide along them.

Intermediate Felments. Microfibrils (Microthreads) are an important element of the cytoskeleton, called because they are smaller in size compared to microtubules 8-10 Nm. Intermediate filaments can be located in bundles, most of them in a cell are found around the nucleus, as well as in the area of ​​such intercellular contacts as dismosomes and semi-dismosomes, as well as in the processes of nerve cells in the form of neurofibrils, intermediate filaments consist of proteins and for each type of cell there is its specific protein. For example, epithelial cells consist of cytokerotene. In fibroblasts, the neurocytes are called vimentin. In muscle cells this protein is mesnin, and in nerve cells the protein is a neurofiloment enzyme. Nuclear Lamin forms one of the plates of the nuclear envelope.