The unity of the structure of cells.
The content of any cell is separated from the external environment by a special structure - plasma membrane (plasmalemma). This isolation allows you to create a very special environment inside the cell, unlike what surrounds it. Therefore, processes that do not occur anywhere can occur in the cell, they are called vital processes.
The internal environment of a living cell, limited by the plasma membrane, is called cytoplasm. It includes hyaloplasm(basic transparent substance) and cell organelles, as well as various non-permanent structures - inclusion. Organelles that are in any cell also include ribosomes, on which there is protein synthesis.
The structure of eukaryotic cells.
Eukaryotes are organisms whose cells have a nucleus. Core- this is the very organelle of the eukaryotic cell, in which the hereditary information recorded in the chromosomes is stored and from which it is rewritten. Chromosome is a DNA molecule integrated with proteins. The core contains nucleolus- a place where other important organelles involved in protein synthesis are formed - ribosomes. But ribosomes are only formed in the nucleus, and they work (i.e., synthesize protein) in the cytoplasm. Some of them are freely located in the cytoplasm, and some attach to membranes, form a mesh, which is called endoplasmic.
Ribosomes- non-membrane organelles.
Endoplasmic reticulum is a network of tubules bounded by membranes. There are two types: smooth and granular. Ribosomes are located on the membranes of the granular endoplasmic reticulum, so proteins are synthesized and transported in it. And the smooth endoplasmic reticulum is the place for the synthesis and transport of carbohydrates and lipids. There are no ribosomes on it.
For the synthesis of proteins, carbohydrates and fats, energy is needed, which is produced in the eukaryotic cell by the "energy stations" of the cell - mitochondria.
Mitochondria- two-membrane organelles in which the process of cellular respiration is carried out. Organic compounds are oxidized on mitochondrial membranes and chemical energy accumulates in the form of special energy molecules (ATP).
There is also a place in the cell where organic compounds can accumulate and from where they can be transported - this is Golgi apparatus, system of flat membrane bags. It is involved in the transport of proteins, lipids, carbohydrates. In the Golgi apparatus, organelles of intracellular digestion are also formed - lysosomes.
Lysosomes- one-membrane organelles, characteristic of animal cells, contain enzymes that can break down proteins, carbohydrates, nucleic acids, lipids.
A cell may contain organelles that do not have a membrane structure, for example, ribosomes and cytoskeleton.
Cytoskeleton- This is the musculoskeletal system of the cell, includes microfilaments, cilia, flagella, a cell center that produces microtubules and centrioles.
There are organelles that are characteristic only of plant cells - plastids. There are: chloroplasts, chromoplasts and leukoplasts. The process of photosynthesis takes place in chloroplasts.
In plant cells also vacuoles- Cell waste products, which are reservoirs of water and compounds dissolved in it. The eukaryotic organisms include plants, animals, and fungi.
The structure of prokaryotic cells.
Prokaryotes- unicellular organisms, in the cells of which there is no nucleus.
Prokaryotic cells are small in size and retain genetic material in the form of a circular DNA molecule (nucleoid). Prokaryotic organisms include bacteria and cyanobacteria, formerly called blue-green algae.
If the process of aerobic respiration occurs in prokaryotes, then special protrusions of the plasma membrane are used for this - mesosomes. If the bacteria are photosynthetic, then the process of photosynthesis occurs on photosynthetic membranes - thylakoids.
Protein synthesis in prokaryotes occurs on ribosomes. There are few organelles in prokaryotic cells.
Hypotheses of the origin of eukaryotic cell organelles.
Prokaryotic cells appeared on Earth earlier than eukaryotic ones.
1) symbiotic hypothesis explains the mechanism of the emergence of some organelles of the eukaryotic cell - mitochondria and photosynthetic plastids.
2) The invaginating hypothesis- claims that the origin of the eukaryotic cell comes from the fact that the ancestral form was an aerobic prokaryote. Organelles in it arose as a result of invagination and detachment of parts of the membrane with subsequent functional specialization in the nucleus, mitochondria, chloroplasts of other organelles.
Eukaryotic cells from the simplest organisms to the cells of higher plants and mammals, differ in the complexity and diversity of the structure. Typical eukaryotic cell does not exist, but common features can be distinguished from thousands of cell types. Each eukaryotic cell consists of cytoplasm and nucleus.
Structure eukaryotic cell.
Plasmalemma(cell membrane) of animal cells is formed by a membrane covered from the outside with a layer of glycocalyx 10-20 nm thick. Plasmalemma performs delimiting, barrier, transport and receptor functions. Due to the property of selective permeability, the plasmalemma regulates the chemical composition of the internal environment of the cell. The plasmalemma contains receptor molecules that selectively recognize certain biologically active substances (hormones). In layers and layers, adjacent cells are retained due to the presence of different types of contacts, which are represented by sections of the plasmalemma that have a special structure. From the inside, the cortical (cortical) layer is adjacent to the membrane cytoplasm with a thickness of 0.1-0.5 microns.
Cytoplasm. In the cytoplasm, there is a number of formed structures that have regular structural and behavioral features at different periods of the cell's life. Each of these structures has a specific function. Hence, they were compared with the organs of the whole organism, in connection with which they received the name organelles, or organelles... Various substances are deposited in the cytoplasm - inclusions (glycogen, fat drops, pigments). The cytoplasm is permeated with membranes endoplasmic reticulum.
Endoplasmic reticulum (EMF)... The endoplasmic reticulum is a branched network of channels and cavities in the cytoplasm of a cell, formed by membranes. On the membranes of the channels there are numerous enzymes that ensure the vital activity of the cell. There are 2 types of EMF membranes - smooth and rough. On membranes smooth endoplasmic reticulum there are enzyme systems involved in fat and carbohydrate metabolism. Main function rough endoplasmic reticulum- protein synthesis, which is carried out in ribosomes attached to membranes. Endoplasmic reticulum- This is a general intracellular circulation system, through the channels of which substances are transported inside the cell and from cell to cell.
Ribosomes carry out the function of protein synthesis. Ribosomes are spherical particles with a diameter of 15-35 nm, consisting of 2 subunits of unequal sizes and containing approximately equal amounts of proteins and RNA. Ribosomes in the cytoplasm are located or attached to the outer surface of the membranes of the endoplasmic reticulum. Depending on the type of synthesized protein, ribosomes can combine into complexes - polyribosomes... Ribosomes are present in all types of cells.
Golgi complex. The main structural element Golgi complex is a smooth membrane that forms packets of flattened cisterns, or large vacuoles, or small vesicles. The cisterns of the Golgi complex are connected to the channels of the endoplasmic reticulum. Proteins, polysaccharides, and fats synthesized on the membranes of the endoplasmic reticulum are transported to the complex, condense inside its structures and "packaged" in the form of a secretion ready for release, or are used in the cell itself during its life.
Mitochondria. The general distribution of mitochondria in the animal and plant world indicates the important role that mitochondria play in the cage. Mitochondria have the form of spherical, oval and cylindrical bodies, can be filiform. The size of mitochondria is 0.2-1 microns in diameter, up to 5-7 microns in length. The length of filamentary forms reaches 15-20 microns. The number of mitochondria in the cells of different tissues is not the same, there are more of them where synthetic processes are intense (liver) or energy expenditure is high. The mitochondrial wall consists of 2 membranes - outer and inner. The outer membrane is smooth, and partitions - ridges, or cristae - extend from the inner to the inside of the organoid. Numerous enzymes involved in energy metabolism are located on the membranes of the cristae. The main function of mitochondria - synthesis of ATP.
Lysosomes- small oval bodies with a diameter of about 0.4 microns, surrounded by one three-layer membrane. Lysosomes contain about 30 enzymes capable of cleaving proteins, nucleic acids, polysaccharides, lipids, and other substances. The breakdown of substances using enzymes is called lysis, therefore the organoid is named lysosome... It is believed that lysosomes are formed from the structures of the Golgi complex or directly from the endoplasmic reticulum. Functions of lysosomes : intracellular digestion of nutrients, destruction of the structure of the cell itself during its death during embryonic development, when embryonic tissues are replaced with permanent ones, and in a number of other cases.
Centrioles. The cell center consists of 2 very small cylindrical bodies located at right angles to each other. These little bodies are called centrioles... The centriole wall consists of 9 pairs of microtubules. Centrioles are capable of self-assembly and belong to the self-reproducing organelles of the cytoplasm. Centrioles play an important role in cell division: they start the growth of microtubules that form the spindle of division.
Core. The nucleus is the most important component of the cell. It contains DNA molecules and therefore performs two main functions: 1) storage and reproduction of genetic information, 2) regulation of metabolic processes in the cell. Lost cell core, cannot exist. The nucleus is also incapable of independent existence. Most cells have one nucleus, but 2-3 nuclei can be observed in one cell, for example, in liver cells. There are known multinucleated cells with several tens of nuclei. The shapes of the nuclei depend on the shape of the cell. The nuclei are spherical, multi-bladed. The core is surrounded by a shell consisting of two membranes with the usual three-layer structure. The outer nuclear membrane is covered with ribosomes, the inner membrane is smooth. The main role in the vital activity of the nucleus is played by the metabolism between the nucleus and the cytoplasm. The contents of the nucleus include nuclear juice, or karyoplasm, chromatin and nucleolus. The composition of nuclear juice includes various proteins, including most of the enzymes of the nucleus, free nucleotides, amino acids, products of the activity of the nucleolus and chromatin, moving from the nucleus to the cytoplasm. Chromatin contains DNA, proteins and is a coiled and compacted sections of chromosomes. Nucleolus is a dense rounded body located in the nuclear juice. The number of nucleoli ranges from 1 to 5-7 or more. Nucleoli are present only in non-dividing nuclei; during mitosis, they disappear, and after the completion of division, they are formed again. The nucleolus is not an independent cell organoid; it lacks a membrane and forms around the chromosome region in which the rRNA structure is encoded. Ribosomes are formed in the nucleolus, which then move into the cytoplasm. Chromatin lumps, granules and reticular structures of the nucleus are called, which are intensely stained with some dyes and are different in shape from the nucleolus.
A cell is an elementary unit of the structure and vital activity of all alive organisms(except viruses, which are often spoken of as non-cellular forms of life), which has its own metabolism, is capable of independent existence, self-reproduction and development. All living organisms either, as multicellular animals, plants and mushrooms, consist of many cells, or, as many protozoa and bacteria are unicellular organisms... The section of biology dealing with the study of the structure and vital activity of cells was named cytology... Recently, it is also customary to talk about cell biology, or cell biology.
Distinctive features of plant and animal cells
|
Signs |
Plant cell |
Animal cage |
|
Plastids |
Chloroplasts, chromoplasts, leukoplasts |
Absent |
|
Food method |
Autotrophic (phototrophic, chemotrophic) | |
|
ATP synthesis |
In chloroplasts, mitochondria |
In mitochondria |
|
Cleavage of ATP |
In chloroplasts and all parts of the cell where energy is needed |
In all parts of the cell where energy is needed |
|
Cell center |
In lower plants |
In all cells |
|
Cellulose cell wall |
Located outside of the cell membrane |
Absent |
|
Inclusions |
Reserve nutrients in the form of starch grains, protein, oil drops; vacuoles with cell sap; salt crystals |
Reserve nutrients in the form of grains and drops (proteins, fats, carbohydrates, glycogen); metabolic end products, salt crystals, pigments |
|
Large cavities filled with cell sap - an aqueous solution of various substances (spare or final products). Osmotic reservoirs of the cell. |
Contractile, digestive, excretory vacuoles. Usually small. |
General signs 1. The unity of structural systems - cytoplasm and nucleus. 2. The similarity of the processes of metabolism and energy. 3. Unity of the principle of the hereditary code. 4. Universal membrane structure. 5. The unity of the chemical composition. 6. The similarity of the process of cell division.
Cell structure
All cellular life forms on Earth can be divided into two kingdoms based on the structure of their constituent cells:
prokaryotes (prenuclear) are simpler in structure and arose earlier in the process of evolution;
eukaryotes (nuclear) - more complex, arose later. The cells that make up the human body are eukaryotic.
Despite the variety of forms, the organization of cells of all living organisms is subordinated to uniform structural principles.
The contents of the cell are separated from the environment by the plasma membrane, or plasma membrane. Inside the cell is filled with cytoplasm, in which various organoids and cellular inclusions are located, as well as genetic material in the form of a DNA molecule. Each of the organoids of the cell performs its own special function, and in aggregate they all determine the vital activity of the cell as a whole.
Prokaryotic cell
The structure of a typical prokaryotic cell: capsule, cell wall, plasmolemma, cytoplasm,ribosomes, plasmid, drank, flagellum,nucleoid.
Prokaryotes (from lat. pro- before, before and Greek κάρῠον - core, nut) - organisms that do not possess, unlike eukaryotes, a formed cell nucleus and other internal membrane organelles (with the exception of flat cisterns in photosynthetic species, for example, in cyanobacteria). The only large circular (in some species - linear) double-stranded molecule DNA, which contains the bulk of the genetic material of the cell (the so-called nucleoid) does not form a complex with proteins histones(so called chromatin). Prokaryotes include bacteria, including cyanobacteria(blue-green algae), and archaea... The descendants of prokaryotic cells are organelles eukaryotic cells - mitochondria and plastids... The main content of the cell, which fills its entire volume, is a viscous granular cytoplasm.
Eukaryotic cell
Eukaryotes are organisms that, in contrast to prokaryotes, have a formalized cellular core separated from the cytoplasm by the nuclear envelope. The genetic material is enclosed in several linear double-stranded DNA molecules (depending on the type of organisms, their number per nucleus can vary from two to several hundred), attached from the inside to the membrane of the cell nucleus and forming in the vast majority (except dinoflagellates) a complex with proteins histones called chromatin... In eukaryotic cells there is a system of internal membranes, which, in addition to the nucleus, form a number of other organoids (endoplasmic reticulum, Golgi apparatus and etc.). In addition, the vast majority have permanent intracellular symbionts- prokaryotes - mitochondria, and in algae and plants - also plastids.
The structure of the eukaryotic cell
A schematic representation of an animal cell. (When you click on any of the names of the component parts of the cell, you will go to the corresponding article.)
Surface complex of an animal cell
Consists of glycocalyx, plasmalemma and the cortical layer located under it cytoplasm... The plasma membrane is also called the plasmalemma, the outer cell membrane. It is a biological membrane, about 10 nanometers thick. First of all, it provides a delimiting function in relation to the environment external to the cell. In addition, she performs transport function... The cell does not spend energy to maintain the integrity of its membrane: the molecules are retained according to the same principle by which fat molecules are held together - hydrophobic it is thermodynamically more favorable for parts of molecules to be located in close proximity to each other. Glycocalyx is a molecule of oligosaccharides, polysaccharides, glycoproteins and glycolipids "anchored" in the plasma membrane. Glycocalyx performs receptor and marker functions. Plasma membrane animals cells mainly consists of phospholipids and lipoproteins with embedded molecules of proteins, in particular, surface antigens and receptors. In the cortical (adjacent to the plasma membrane) layer of the cytoplasm, there are specific elements of the cytoskeleton - actin microfilaments ordered in a certain way. The main and most important function of the cortical layer (cortex) is pseudopodial reactions: ejection, attachment and contraction of pseudopodia. In this case, the microfilaments are rearranged, lengthened or shortened. The shape of the cell also depends on the structure of the cytoskeleton of the cortical layer (for example, the presence of microvilli).
The cells that form the tissues of animals and plants vary significantly in shape, size and internal structure. However, they all show similarities in the main features of vital processes, metabolism, irritability, growth, development, and the ability to change.
Cells of all types contain two main components that are closely related to each other - the cytoplasm and the nucleus. The nucleus is separated from the cytoplasm by a porous membrane and contains nuclear juice, chromatin and nucleolus. The semi-liquid cytoplasm fills the entire cell and is permeated with numerous tubules. Outside, it is covered with a cytoplasmic membrane. It has specialized organelle structures, permanently present in the cell, and temporary formations - inclusion.Membrane organelles : outer cytoplasmic membrane (HCM), endoplasmic reticulum (EPS), Golgi apparatus, lysosomes, mitochondria and plastids. The structure of all membrane organelles is based on a biological membrane. All membranes have a fundamentally unified structural plan and consist of a double layer of phospholipids, into which protein molecules are immersed from different sides of willow of different depths. Organoid membranes differ from each other only by the sets of proteins included in them.
Diagram of the structure of a eukaryotic cell. A - a cell of animal origin; B - plant cell: 1 - nucleus with chromatin and nucleolus, 2 - cytoplasmic membrane, 3- cell wall, 4 - pores in the cell wall through which the cytoplasm of neighboring cells communicates, 5 - rough endoplasmic reticulum, b - smooth endoplasmic reticulum, 7 - pinocytic vacuole, 8 - Golgi apparatus (complex), 9 - lysosome, 10 - fatty inclusions in the channels of the smooth endoplasmic reticulum, 11 - cell center, 12 - mitochondria, 13 - free ribosomes and polyribosomes, 14 - vacuole, 15 - chloroplast
Cytoplasmic membrane. In all plant cells, multicellular animals, protozoa and bacteria, the cell membrane is three-layered: the outer and inner layers consist of protein molecules, and the middle layer consists of lipid molecules. It limits the cytoplasm from the external environment, surrounds all cell organelles and represents a universal biological structure. In some cells, the outer membrane is formed by several membranes that fit tightly to each other. In such cases, the cell membrane becomes dense and elastic and allows you to maintain the shape of the cell, as, for example, in euglena and ciliate shoes. Most plant cells, in addition to the membrane, also have a thick cellulose shell outside - cell wall... It is clearly visible in a conventional light microscope and performs a supporting function due to the rigid outer layer, which gives the cells a clear shape.
On the cell surface, the membrane forms elongated outgrowths - microvilli, folds, protrusions and protrusions, which greatly increases the absorbing or excretory surface. With the help of membrane outgrowths, cells are connected to each other in the tissues and organs of multicellular organisms; various enzymes involved in metabolism are located on the folds of the membranes. By delimiting the cell from the environment, the membrane regulates the direction of diffusion of substances and at the same time actively transfers them into the cell (accumulation) or outward (release). Due to these properties of the membrane, the concentration of potassium, calcium, magnesium, phosphorus ions in the cytoplasm is higher, and the concentration of sodium and chlorine is lower than in the environment. Through the pores of the outer membrane from the external environment, ions, water and small molecules of other substances penetrate into the cell. Penetration of relatively large solid particles into the cell is carried out by phagocytosis(from the Greek "phago" - I devour, "pitoe" - a cell). In this case, the outer membrane at the point of contact with the particle bends into the cell, dragging the particle into the depths of the cytoplasm, where it undergoes enzymatic cleavage. Drops of liquid substances enter the cell in a similar way; their absorption is called pinocytosis(from the Greek "pino" - I drink, "cytos" - a cell). The outer cell membrane also has other important biological functions.
Cytoplasm 85% consists of water, 10% - of proteins, the rest is the share of lipids, carbohydrates, nucleic acids and mineral compounds; all these substances form a colloidal solution similar in consistency to glycerin. The colloidal substance of a cell, depending on its physiological state and the nature of the impact of the external environment, has the properties of both a liquid and an elastic, denser body. The cytoplasm is permeated with channels of various shapes and sizes, which are called endoplasmic reticulum. Their walls are membranes that are in close contact with all organelles of the cell and together with them constitute a single functional and structural system for the metabolism and energy and movement of substances inside the cell.
In the walls of the tubules are the smallest grains-granules, called ribosomes. This network of tubules is called granular. Ribosomes can be scattered on the surface of the tubules or form complexes of five to seven or more ribosomes, called polysomes. Other tubules do not contain granules; they constitute a smooth endoplasmic reticulum. The walls contain enzymes involved in the synthesis of fats and carbohydrates.
The inner cavity of the tubules is filled with waste products of the cell. Intracellular tubules, forming a complex branching system, regulate the movement and concentration of substances, separate various molecules of organic substances and the stages of their synthesis. On the inner and outer surfaces of the enzyme-rich membranes, proteins, fats and carbohydrates are synthesized, which are either used in metabolism, or accumulate in the cytoplasm as inclusions, or are excreted.
Ribosomes found in all types of cells - from bacteria to cells of multicellular organisms. These are rounded bodies made up of ribonucleic acid (RNA) and proteins in almost equal proportions. They certainly include magnesium, the presence of which supports the structure of the ribosomes. Ribosomes can be associated with the membranes of the endoplasmic reticulum, with the outer cell membrane, or lie freely in the cytoplasm. Protein synthesis is carried out in them. Ribosomes, in addition to the cytoplasm, are found in the cell nucleus. They are formed in the nucleolus and then enter the cytoplasm.
Golgi complex in plant cells it looks like separate bodies surrounded by membranes. In animal cells, this organoid is represented by cisterns, tubules and vesicles. The products of cell secretion enter the membrane tubes of the Golgi complex from the tubules of the endoplasmic reticulum, where they are chemically rearranged, compacted, and then transferred into the cytoplasm and either used by the cell itself or excreted from it. In the cisterns of the Golgi complex, polysaccharides are synthesized and combined with proteins, resulting in the formation of glycoproteins.
Mitochondria- small rod-shaped bodies, limited by two membranes. Numerous folds - cristae - extend from the inner membrane of the mitochondria; various enzymes are located on their walls, with the help of which a high-energy substance, adenosine triphosphoric acid (ATP), is synthesized. Depending on the activity of the cell and external influences, mitochondria can move, change their size and shape. Ribosomes, phospholipids, RNA and DNA are found in mitochondria. The presence of DNA in mitochondria is associated with the ability of these organelles to reproduce by forming a constriction or budding during cell division, as well as the synthesis of a part of mitochondrial proteins.
Lysosomes- small oval formations, limited by a membrane and scattered throughout the cytoplasm. Found in all cells of animals and plants. They arise in the extensions of the endoplasmic reticulum and in the Golgi complex, here they are filled with hydrolytic enzymes, and then they separate and enter the cytoplasm. Under normal "conditions, lysosomes digest particles that enter the cell by phagocytosis, and organelles of dying cells. Lysis products are excreted through the lysosome membrane into the cytoplasm, where they are incorporated into new molecules. When the lysosome membrane breaks, enzymes enter the cytoplasm and digest its contents, causing cell death.
Plastids is found only in plant cells and is found in most green plants. Organic substances are synthesized and accumulated in plastids. There are three types of plastids: chloroplasts, chromoplasts and leukoplasts.
Chloroplasts - green plastids containing the green pigment chlorophyll. They are found in leaves, young stems, unripe fruits. Chloroplasts are surrounded by a double membrane. In higher plants, the inner part of chloroplasts is filled with a semi-liquid substance, in which plates are laid parallel to each other. Paired membranes of the plates, merging, form stacks containing chlorophyll (Fig. 6). In each stack of chloroplasts of higher plants, layers of protein molecules and lipid molecules alternate, and chlorophyll molecules are located between them. This layered structure maximizes free surfaces and facilitates energy capture and transfer during photosynthesis.
Chromoplasts - plastids, which contain plant pigments (red or brown, yellow, orange). They are concentrated in the cytoplasm of cells of flowers, stems, fruits, leaves of plants and give them the appropriate color. Chromoplasts are formed from leukoplasts or chloroplasts as a result of the accumulation of pigments carotenoids.
Leukoplasts-colorless plastids located in uncolored parts of plants: in stems, roots, bulbs, etc. In the leukoplasts of some cells, starch grains accumulate, in the leukoplasts of other cells - oils and proteins.
All plastids arise from their predecessors - proplastids. They contain DNA that controls the reproduction of these organelles.
Cell center, or centrosome, plays an important role in cell division and consists of two centrioles . It is found in all cells of animals and plants, except for flowering, lower fungi and some of the simplest. Centrioles in dividing cells take part in the formation of the fission spindle and are located at its poles. In a dividing cell, the cell center is the first to divide, at the same time an achromatin spindle is formed, which orientates the chromosomes when they diverge to the poles. One centriole goes into the daughter cells.
Many plant and animal cells have organelles for special purposes: cilia, performing the function of movement (ciliates, cells of the respiratory tract), flagella(the simplest unicellular, male reproductive cells in animals and plants, etc.). Inclusions - temporary elements arising in a cell at a certain stage of its life as a result of a synthetic function. They are either used or taken out of the cell. Inclusions are also reserve nutrients: in plant cells - starch, fat droplets, blobs, essential oils, many organic acids, salts of organic and inorganic acids; in animal cells - glycogen (in liver cells and muscles), fat drops (in subcutaneous tissue); Some inclusions accumulate in cells as waste - in the form of crystals, pigments, etc.
Vacuoles - these are cavities bounded by a membrane; well expressed in plant cells and are found in protozoa. They arise in different areas of the endoplasmic reticulum extensions. And gradually separate from it. Vacuoles maintain turgor pressure, they contain cellular or vacuolar juice, the molecules of which determine its osmotic concentration. It is believed that the initial products of synthesis - soluble carbohydrates, proteins, pectins, etc. - accumulate in the cisterns of the endoplasmic reticulum. These clusters represent the rudiments of future vacuoles.
Cytoskeleton . One of the distinctive features of a eukaryotic cell is the development of skeletal formations in its cytoplasm in the form of microtubules and bundles of protein fibers. The elements of the cytoskeleton are closely related to the outer cytoplasmic membrane and the nuclear envelope, and form complex weaves in the cytoplasm. The supporting elements of the cytoplasm determine the shape of the cell, provide the movement of intracellular structures and the movement of the entire cell.
Core the cell plays a major role in its life, with its removal, the cell stops its functions and dies. Most animal cells have one nucleus, but there are also multinucleated cells (human liver and muscles, mushrooms, ciliates, green algae). Mammalian red blood cells develop from progenitor cells containing a nucleus, but mature red blood cells lose it and do not live long.
The nucleus is surrounded by a double membrane permeated with pores, through which it is closely connected with the channels of the endoplasmic reticulum and the cytoplasm. Inside the core is chromatin- spiralized sections of chromosomes. During the period of cell division, they turn into rod-shaped structures that are clearly distinguishable under a light microscope. Chromosomes are a complex complex of proteins with DNA called nucleoprotein.
The functions of the nucleus are to regulate all vital functions of the cell, which it carries out with the help of DNA and RNA material carriers of hereditary information. In preparation for cell division, DNA doubles; in the process of mitosis, chromosomes diverge and are transmitted to daughter cells, ensuring the continuity of hereditary information in each type of organism.
Karyoplasm - the liquid phase of the nucleus, in which the waste products of nuclear structures are in dissolved form
Nucleolus- the isolated, most dense part of the nucleus. The nucleolus contains complex proteins and RNA, free or bound phosphates of potassium, magnesium, calcium, iron, zinc, and ribosomes. The nucleolus disappears before the start of cell division and re-forms in the last phase of division.
Thus, the cell has a delicate and highly complex organization. An extensive network of cytoplasmic membranes and the membrane principle of the structure of organelles make it possible to distinguish between many chemical reactions simultaneously occurring in the cell. Each of the intracellular formations has its own structure and specific function, but only with their interaction is the harmonious vital activity of the cell possible. On the basis of this interaction, substances from the environment enter the cell, and waste products are removed from it into the external environment - this is how metabolism takes place. The perfection of the structural organization of the cell could arise only as a result of prolonged biological evolution, in the process of which the functions performed by it gradually became more complicated.
The simplest unicellular forms are both a cell and an organism with all its vital manifestations. In multicellular organisms, cells form homogeneous groups - tissues. In turn, tissues form organs, systems, and their functions are determined by the general vital activity of the whole organism.
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