1. Glycocalyx 2. Microvilli 3. Intercellular contact in the form of a "castle" 4. Desmosome 5. Tight contact

Microvilli are an integral part of thin and thick epithelial cells.

intestines, kidney tubules. In these organs, microvilli provide absorption

necessary substances. The number of microvilli (2) in one cell can reach 3000. A large number of microvilli in a cell creates narrow gaps between them. In these

spaces, capillary forces act, contributing to the suction of the liquid. In the small intestine, on the microvilli of the surface epithelium, in the glycocalyx (1) and in the plasmolemma, enzymes are concentrated that provide parietal digestion and absorption of substances.

In the kidneys, microvilli absorb water and electrolytes, which later pass into the blood. In some pathological conditions, the microvilli separate from the cell and close the lumen of the renal tubule (protein cylinder syndrome)

Name the structures indicated by numbers, explain the functions of these structures.

Special cell surface structures: microcilia in epitheliocytes

1. Microcilium 2. Axoneme 3. Basal body 4. Desmosome 5. Basement membrane

6. Plasma membrane

Microcilia are classified as specialized cell organelles. They always

present in the epithelium of the airways, in the oviduct and have mobility.

A microcilium is an outgrowth of a cell with a diameter of 300 nm. Outside, it is covered by a plasmolemma (6), and inside there is an axoneme (2), which consists of complexes of microtubules. Microtubules are assembled into complexes in the form of doublets: 9 pairs on the periphery and one pair in the center. Microcilia are built from the protein tubulin, which is incapable of contraction. The movement of microcilia is provided by the protein dynein, which is localized in the “handles” of microtubule doublets.

The axoneme (2) is connected to the basal body (3), which consists of triplets of microtubules without a central doublet.

The development of microcilia is associated with the formation of a cell center. During this period, multiple reduplication of centrioles occurs. New centrioles migrate in pairs to the apical surface of the cell. Here they are modified into microcilia.

Give a name to the process and its phases. Describe the changes that occur in each of the above diagrams.

Mitosis.

1. Cell in interphase 2. Prophase. Chromosomes spiralize. The shell of the nucleus disintegrates. Centrioles diverge to the poles of the cell 3. Early anaphase. Comes after metaphase. In this case, the chromosomes move to the poles at a speed of 0.2-5.0 microns per minute. 4. Telophase. Organization of nuclei in daughter cells occurs.

In the premitotic phase (1), the number of chromosomes doubles in the cell.

Schemes 2,3,4 show the main phases of mitosis. Transcription stops in prophase. Then the spiralization of chromosomes begins. By the end of prophase, chromosomes are visible, each of which consists of two chromatids. The chromatids are intertwined and are not seen separately. characteristic feature prophase is the formation of the fission spindle. Two centrioles depart from each pole and microtubules form from them. The formation of microtubules is provided by the polymerization of tubulin proteins. Chromosomes bind to microtubules.

Metaphase takes 20-30 minutes. During this period, the formation of the fission spindle is completed and the chromosomes occupy the equatorial plane. At the end of metaphase, sister chromatids separate.

In anaphase (2), sister chromatids become independent chromosomes and diverge towards the poles. Telophase is divided into early and late (3,4). Early telophase is the completion of chromosome segregation. In the late telophase, the formation of new nuclei begins, the isolation genetic material(3). The late telephase ends with the division of the original cell into two daughter cells (cytokinesis or cytotomy).

Chromosomes begin to transcribe RNA. By the end of telophase, the nucleolus is fully developed.

And in collar-flagellated cells of sponges and other multicellular animals. In humans, microvilli have epithelial cells of the small intestine, on which microvilli form a brush border, as well as mechanoreceptors of the inner ear - hair cells.

Microvilli are often confused with cilia, but they are very different in structure and function. Cilia have a basal body and a microtubule cytoskeleton, are capable of rapid movements (except for modified immobile cilia) and in large metazoans usually serve to create fluid currents or perceive stimuli, and in unicellular and small metazoans also for locomotion. Microvilli do not contain microtubules and are only capable of slow bending (in the intestine) or immobile.

Auxiliary proteins that interact with actin are responsible for ordering the actin cytoskeleton of microvilli - fimbrin, spectrin, villin, etc. Microvilli also contain several varieties of cytoplasmic myosin.

Intestinal microvilli (not to be confused with multicellular villi) greatly increase the surface area of ​​absorption. In addition, in vertebrates, digestive enzymes are fixed on their plasmalemma, which provide parietal digestion.

The microvilli of the inner ear (stereocilia) are interesting in that they form rows with different, but strictly defined lengths in each row. The tops of the microvilli of the shorter row are connected to the longer microvilli of the neighboring row with the help of proteins - protocadherins. Their absence or destruction can lead to deafness, since they are necessary for opening sodium channels on the hair cell membrane and, therefore, for converting the mechanical energy of sound into a nerve impulse.

Although microvilli persist on hair cells throughout life, each of them is constantly renewed by treadmilling of actin filaments.

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An excerpt characterizing the microvilli

It was already late in the evening when they went up to the Olmutsky Palace, occupied by the emperors and their entourage.
On that very day there was a council of war, in which all the members of the Hofkriegsrat and both emperors participated. At the council, contrary to the opinion of the old people - Kutuzov and Prince Schwarzernberg, it was decided to immediately advance and give a general battle to Bonaparte. The military council had just ended when Prince Andrei, accompanied by Boris, came to the palace in search of Prince Dolgorukov. Still all the faces of the main apartment were under the charm of today's military council, victorious for the party of the young. The voices of the procrastinators, advising to expect something else without attacking, were so unanimously muffled and their arguments refuted by undeniable evidence of the benefits of the offensive, that what was being discussed in the council, the future battle and, no doubt, victory, seemed no longer the future, but the past. All benefits were on our side. Huge forces, no doubt superior to those of Napoleon, were drawn into one place; the troops were animated by the presence of the emperors and rushed into action; the strategic point at which they had to act was known to the smallest detail to the Austrian general Weyrother, who led the troops (as if by a lucky chance, the Austrian troops were on maneuvers last year on precisely those fields in which they now had to fight the French); the present terrain was known to the smallest detail and shown on maps, and Bonaparte, apparently weakened, did nothing.
Dolgorukov, one of the most ardent supporters of the offensive, had just returned from the council, tired and exhausted, but animated and proud of the victory he had won. Prince Andrei introduced the officer he patronized, but Prince Dolgorukov, after shaking his hand politely and firmly, said nothing to Boris and, apparently unable to refrain from expressing those thoughts that most occupied him at that moment, turned in French to Prince Andrei.
- Well, my dear, what a battle we fought! God only grant that that which will be the result of it would be just as victorious. However, my dear,” he said in fragmentary and animated terms, “I must confess my guilt before the Austrians and especially before Weyrother. What precision, what detail, what knowledge of the terrain, what foresight of all possibilities, all conditions, all the smallest details! No, my dear, it is impossible to invent anything more advantageous than the conditions in which we find ourselves. The combination of Austrian distinctness with Russian courage - what else do you want?
“So the offensive is finally decided?” Bolkonsky said.

Microtubules also play a structural role in cells: these long, tubular, rather rigid structures form the supporting system of the cell, being part of cytoskeleton. They help determine the shape of cells in the process of differentiation and maintain the shape of differentiated cells; often they are located in the zone directly adjacent to the plasma membrane. Animal cells in which the microtubule system is damaged take on a spherical shape. In plant cells, the arrangement of microtubules exactly corresponds to the arrangement of cellulose fibers deposited during the construction of the cell wall; thus microtubules indirectly determine the shape of the cell.

microvilli

microvilli called finger-like outgrowths plasma membrane some animal cells. Sometimes microvilli increase the surface area of ​​the cell by 25 times, so they are especially numerous on the surface of cells of the suction type, namely in the epithelium of the small intestine and convoluted tubules of nephrons. This increase in absorptive surface area also contributes to better digestion of food in the intestines, because some digestive enzymes are located on the surface of the cells and are associated with it.

Fringe of microvilli on epithelial cells is clearly visible in a light microscope; this is the so-called brush border of the epithelium.

In every microvillus contains bundles of actin and myosin filaments. Actin and myosin are muscle proteins involved in muscle contraction. At the base of the microvilli, actin and myosin filaments bind to the filaments of neighboring microvilli to form a complex network. This whole system as a whole maintains the microvilli in a straightened state and allows them to maintain their shape, while at the same time ensuring the sliding of actin filaments along myosin filaments (similar to what happens during muscle contraction).

An electron micrograph showing cellulose fibers in individual ayus of the cell wall of the green seaweed Chaetomorpha melagonium. The thickness of cellulose microfibrils is 20 nm. To obtain a contrast image, the alloy of platinum and gold was drunk.

Cell walls

Plant cells, like the cells of prokaryotes and fungi, are enclosed in a relatively rigid cell wall, the material for the construction of which is secreted by the cell wall itself. living cell(protoplast). In terms of their chemical composition, plant cell walls differ from those of prokaryotes and fungi.

cell wall deposited during plant cell division is called the primary cell wall. Later, as a result of thickening, it can turn into a secondary cell wall. The figure reproduces an electron micrograph, which shows one of the early stages of this process.

The structure of the cell wall

primary cell wall consists of cellulose fibrils embedded in a matrix, which includes other polysaccharides. Cellulose is also a polysaccharide. It has a high tensile strength comparable to that of steel. The matrix consists of polysaccharides, which, for convenience of description, are usually divided into pectins and hemicelluloses. Pectins are acidic polysaccharides with relatively high solubility. The median plate, which holds the walls of neighboring cells together, consists of sticky gelatinous pectates (pectin salts) of magnesium and calcium.

Hemicelluloses are a mixed group of alkali-soluble polysaccharides. Hemicelluloses, like cellulose, have chain-like molecules, but their chains are shorter, less ordered, and more branched.

Cell walls hydrated: 60-70% of their mass is usually water. In the free space of the cell wall, water moves freely.

In some cells, for example, in cells of the mesophyll of a leaf, throughout their life there is only a primary cell wall. However, in most cells, additional layers of cellulose are deposited on the inner surface of the primary cell wall (outside the plasma membrane), i.e., a secondary cell wall appears. In any layer of secondary thickening, cellulose fibers are located at the same angle, but this angle is different in different layers, which ensures even greater strength of the structure. This arrangement of cellulose fibers is shown in the figure.

Some cells, such as tracheal xylem elements and sclerenchyma cells, undergo intense lignification (lignification). In this case, all layers of cellulose are impregnated with lignin - a complex polymeric substance that is not related to polysaccharides. Protoxylem cells are only partially lignified. In other cases, lignification is continuous, except for the so-called pore fields, i.e., those areas in the primary cell wall through which contact is made between neighboring cells using the plasmolema group.

lignin binds cellulose fibers together and holds them in place. It acts as a very hard and rigid matrix that enhances the tensile strength of the cell walls and especially the compressive strength (prevents deflection). This is the main supporting material of the tree. It also protects cells from damage caused by physical and chemical factors. Together with the cellulose remaining in the cell walls, lignin gives the wood its special properties which make it an indispensable building material.

A microvillus is a finger-shaped outgrowth of a eukaryotic (usually animal) cell containing a cytoskeleton of actin microfilaments inside. The collar of choanoflagellate cells and collar-flagellar cells of sponges and other multicellular animals consists of microvilli. In the human body, microvilli have epithelial cells of the small intestine, on which microvilli form a brush border, as well as mechanoreceptors of the inner ear - hair cells. Auxiliary proteins that interact with actin, fimbrin, spectrin, villin, etc., are responsible for ordering the actin cytoskeleton of microvilli. Microvilli also contain cytoplasmic myosin of several varieties.

Organoids: concept, meaning, classification of organelles by prevalence.

Organelles: concept, meaning, classification of organelles by structure.

Organelles: concept, meaning, classification of organelles by function.

Organelles or organelles are the permanent structures of cells in cytology. Each organelle performs certain functions vital for the cell. The term "Organoids" is explained by the comparison of these cell components with the organs of a multicellular organism. Organelles contrast with the temporary inclusions of the cell, which appear and disappear in the process of metabolism.

Classification of organelles by prevalence:

Subdivided into are common characteristic of various cells (ER, ribosomes, lysosomes, mitochondria), and special(supporting threads of tono-fibrils of epithelial cells), found exclusively in cellular elements of one type.

Classification of organelles by structure:

They are subdivided into membrane ones, the structure of which is based on a biological membrane, and non-membrane ones (ribosomes, cell center, microtubules).

Classification of organelles by function:

Synthetic apparatus (ribosomes, ER, Golgi apparatus)

Intracellular digestion apparatus (lysosome and peroxisome)

Energy apparatus (mitochondria)

Cytoskeletal apparatus

Organelles of energy production: concept, location, structure, meaning. (See answer 30)

Mitochondria: concept, location in the cell, structure with light and electron microscopy.

Mitochondria are two-membrane granular or filamentous organelles about 0.5 µm thick.

The process of energy production in mitochondria can be divided into four main stages, the first two of which occur in the matrix, and the last two - on the mitochondrial cristae:

1. The transformation of pyruvate and fatty acids in acetyl-CoA;

2. Oxidation of acetyl-CoA in the Krebs cycle, leading to the formation of NADH;

3. Electron transfer from NADH to oxygen via respiratory chain;

4. Formation of ATP as a result of the activity of the membrane ATP-synthetase complex.

Organelles of intracellular digestion: concept, location, structure, meaning (see answers in 32 and 33)

Lysosomes: concept, structure, location, meaning.

Lysosome is a cellular organoid with a size of 0.2 - 0.4 microns, one of the types of vesicles. These single-membrane organelles are part of the vacuum (endomembrane system of the cell)

Lysosomes are formed from vesicles (vesicles) that are separated from the Golgi apparatus, and vesicles (endosomes), into which substances enter during endocytosis. The membranes of the endoplasmic reticulum take part in the formation of autolysosomes (autophagosomes). All proteins of lysosomes are synthesized on "sessile" ribosomes on the outer side of the membranes of the endoplasmic reticulum and then pass through its cavity and through the Golgi apparatus.

The functions of lysosomes are:

1. digestion of substances or particles captured by the cell during endocytosis (bacteria, other cells)

2. autophagy - the destruction of structures unnecessary to the cell, for example, during the replacement of old organelles with new ones, or the digestion of proteins and other substances produced inside the cell itself

3. autolysis - self-digestion of a cell, leading to its death (sometimes this process is not pathological, but accompanies the development of the organism or the differentiation of some specialized cells). Example: When a tadpole turns into a frog, the lysosomes in the cells of the tail digest it: the tail disappears, and the substances formed during this process are absorbed and used by other cells of the body.

Peroxisomes: concept, structure, location, meaning.

Peroxisome is an essential organelle of a eukaryotic cell, limited by a membrane, containing a large number of enzymes that catalyze redox reactions (D-amino acid oxidases, urate oxidases and catalase). It has a size of 0.2 to 1.5 microns, separated from the cytoplasm by a single membrane.

The set of peroxisome functions differs in different cell types. Among them: the oxidation of fatty acids, photorespiration, the destruction of toxic compounds, the synthesis of bile acids, cholesterol, and ester-containing lipids, the construction of the myelin sheath nerve fibers, phytanic acid metabolism, etc. Along with mitochondria, peroxisomes are the main consumers of O2 in the cell.

Synthesis organelles: concept, varieties, location, structure, meaning. (See answer in 35.36 and 37)

Ribosomes: concept, structure, varieties, meaning.

The ribosome is the most important non-membrane organelle of a living cell, spherical or slightly ellipsoidal in shape, 100-200 angstroms in diameter, consisting of large and small subunits. Ribosomes are used for protein biosynthesis from amino acids according to a given matrix based on genetic information provided by messenger RNA, or mRNA. This process is called translation.

In eukaryotic cells, ribosomes are located on the membranes of the endoplasmic reticulum, although they can also be localized in an unattached form in the cytoplasm. Often several ribosomes are associated with one mRNA molecule, such a structure is called a polyribosome. Synthesis of ribosomes in eukaryotes occurs in a special intranuclear structure - the nucleolus.

Endoplasmic reticulum: concept, structure, varieties, meaning.

The endoplasmic reticulum (EPR) or endoplasmic reticulum (EPS) is an intracellular organelle of a eukaryotic cell, which is a branched system of flattened cavities, vesicles and tubules surrounded by a membrane.

There are two types of EPS:

Granular endoplasmic reticulum;

Agranular (smooth) endoplasmic reticulum.

Golgi apparatus: concept, structure with light and electron microscopy, location.

The Golgi apparatus (Golgi complex) is a membrane structure of a eukaryotic cell, an organelle mainly intended for the excretion of substances synthesized in the endoplasmic reticulum.

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

Organelles of the cytoskeleton: concept, varieties, structure, meaning.

The cytoskeleton is the cell frame or skeleton located in the cytoplasm of a living cell. It is present in all cells in both eukaryotes and prokaryotes. This is a dynamic, changing structure, the function of which is to maintain and adapt the shape of the cell to external influences, exo- and endocytosis, ensuring the movement of the cell as a whole, active intracellular transport and cell division. The cytoskeleton is formed by proteins.

In the cytoskeleton, several main systems are distinguished, called either by the main structural elements, noticeable in electron microscopic studies (microfilaments, intermediate filaments, microtubules), or by the main proteins that make up their composition (actin-myosin system, keratins, tubulin-dynein system).

Special organelles. destination are permanent and obligatory for individual microstructure cells, which perform special functions that provide tissue and organ specialization. These include: cilia, flagella, microvilli, myofibrils.

Cilia and flagella- These are special organelles of movement found in some cells of various organisms. The cilium is a cylindrical outgrowth of the cytoplasm. Inside the outgrowth there is an axoneme (axial thread), the proximal part of the cilium (basal body) is immersed in the cytoplasm. The system of microtubules of the cilia is described by the formula - (9x2) + 2. The main protein of the cilia is tubulin.

Tonofibrils- thin protein fibers that ensure the preservation of shape in some epithelial cells. Tonofibrils provide mechanical strength to cells.

myofibrils- These are organelles of striated muscle cells that ensure their contraction. They serve to contract muscle fibers. Myofibril is a filamentous structure made up of sarcomeres. Each sarcomere is about 2 µm long and contains two types of protein filaments: thin actin microfilaments and thick myosin filaments. The boundaries between filaments (Z-discs) consist of special proteins to which the ± ends of actin filaments are attached. Myosin filaments are also attached to the borders of the sarcomere by filaments of the protein titin (titin). Auxiliary proteins, nebulin and proteins of the troponin-tropomyosin complex, are associated with actin filaments.

In humans, the thickness of myofibrils is 1-2 microns, and their length can reach the length of the entire cell (up to several centimeters). One cell usually contains several tens of myofibrils, they account for up to 2/3 of the dry mass of muscle cells.

Inclusions. Their classification and morpho-functional characteristics.

Inclusions- these are optional and non-permanent components of the cell, arising and disappearing depending on the metabolic state of the cells. Distinguish: trophic, secretory, excretory, pigment inclusions.

To trophic carry droplets of fats., glycogen.

Secretory on.- these are rounded formations of various solutions containing biologically active substances.

Excretory incl..- do not contain any enzymes. These are usually metabolic products to be removed from cells.

Pigmented incl.- can be exogenous (carotene, dust particles, dyes) and endogenous (hemoglobin, bilirubin, melanin, lipofuscin).

The nucleus, its significance in the life of class. The main components of the kernel. Their structural and functional characteristics. Nuclear-cytoplasmic relations as an indicator of the functional state of class.

Core class - is a structure that provides genetic determination, regulation of protein synthesis and the performance of other cellular functions.

Structural elements of the core:1) chromatin; 2) nucleolus; 3) karyoplasm; 4) karyolemma.

Chromatin is a substance that perceives the dye well and consists of chromatin fibrils, 20-25 nm thick, which can be loosely or compactly located in the nucleus. As the cell prepares for division, chromatin fibrils are fused in the nucleus and chromatin is converted into chromosomes. After making in the Nuclei of daughter cells, despiralization of chromatin fibrils occurs. Chromatin is distinguished: EUCHROMATIN – zones of complete decondensation of chromosomes and their regions. Active regions of chromosomes. HETEROCHROMATIN – areas of condensed chromatin. Inactive regions or whole chromosomes. SEX CHROMATIN - the second inactive X chromosome in the cells of the female body.

According to the chemical structure, chromatin consists of:

1) deoxy ribonucleic acid(DNA);

2) proteins;

3) ribonucleic acid (RNA).

The nucleolus is a spherical formation (1-5 microns in diameter), which perceives basic dyes well and is located among the chromatin. The nucleolus is not an independent structure. It is formed only in the interphase. One nucleus contains several nucleoli.

Microscopically, in the nucleolus, the following are distinguished: 1) the fibrillar component (located in the central part of the nucleolus and is a thread of ribonucleoprotein); 2) granular component (located in the peripheral part of the nucleolus and is an accumulation of ribosome subunits). Kiriolemma - the nuclear membrane of the cat., separates the contents of the nucleus from the cytoplasm, provides a regulated metabolism m / d by the nucleus and cytoplasm. The nuclear envelope is involved in the fixation of chromatin.

Functions of somatic cell nuclei:

1) storage of genetic information encoded in DNA molecules;

2) repair (restoration) of DNA damage molecules with the help of special reparative enzymes;

3) reduplication (doubling) of DNA in the synthetic period of interphase.

4) transfer of genetic information to daughter cells during mitosis;

5) implementation of the genetic information encoded in DNA for the synthesis of protein and non-protein molecules: the formation of a protein synthesis apparatus (messenger, ribosomal and transfer RNA).

Functions of germ cell nuclei:

1) storage of genetic information;

2) the transfer of genetic information during the merger of female and male sexual cells.

In the body of mammals and humans, the following types of cells are distinguished:

1) frequently dividing cells of the intestinal epithelium;

2) rarely dividing cells (liver cells); .

3) non-dividing cells ( nerve cells). Life cycle these cell types are different. The cell cycle is divided into two main

1) mitosis, or division period;

2) interphase - the period of cell life between two divisions.