Organelles of a living cell containing DNA. Cell structure. The structure of a plant cell

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The presence of plastids main feature plant cell.

plasma membrane- a thin film, consists of interacting lipid and protein molecules, delimits the internal contents from the external environment, provides transport of water, mineral and organic substances into the cell by osmosis and active transfer, and also removes waste products.

Cytoplasm- the internal semi-liquid environment of the cell, in which the nucleus and organelles are located, provides connections between them, participates in the main processes of life.

Endoplasmic reticulum- a network of branching channels in the cytoplasm. It is involved in the synthesis of proteins, lipids and carbohydrates, in the transport of substances. Ribosomes - bodies located on the EPS or in the cytoplasm, consist of RNA and protein, are involved in protein synthesis. EPS and ribosomes are a single apparatus for the synthesis and transport of proteins.

Mitochondria-organelles separated from the cytoplasm by two membranes. Organic substances are oxidized in them and ATP molecules are synthesized with the participation of enzymes. An increase in the surface of the inner membrane on which enzymes are located due to cristae. ATP is an energy-rich organic substance.

plastids(chloroplasts, leukoplasts, chromoplasts), their content in the cell is the main feature of the plant organism. Chloroplasts are plastids containing the green pigment chlorophyll, which absorbs light energy and uses it to synthesize organic substances from carbon dioxide and water. Delimitation of chloroplasts from the cytoplasm by two membranes, numerous outgrowths - grana on the inner membrane, in which chlorophyll molecules and enzymes are located.

Golgi complex- a system of cavities delimited from the cytoplasm by a membrane. The accumulation of proteins, fats and carbohydrates in them. Implementation of the synthesis of fats and carbohydrates on membranes.

Lysosomes- bodies separated from the cytoplasm by a single membrane. The enzymes contained in them accelerate the reaction of splitting complex molecules to simple ones: proteins to amino acids, complex carbohydrates to simple ones, lipids to glycerol and fatty acids, and also destroy dead parts of the cell, whole cells.

Vacuoles- cavities in the cytoplasm filled with cell sap, a place of accumulation of spare nutrients, harmful substances; they regulate the water content in the cell.

Core - main part cell, covered on the outside with a two-membrane, permeated with pores of the nuclear envelope. Substances enter the core and are removed from it through the pores. Chromosomes are carriers of hereditary information about the characteristics of an organism, the main structures of the nucleus, each of which consists of one DNA molecule in combination with proteins. The nucleus is the site of the synthesis of DNA, i-RNA, r-RNA.

Outer or plasma membrane- separates the contents of the cell from environment(other cells, intercellular substance), consists of lipid and protein molecules, provides communication between cells, transport of substances into the cell (pinocytosis, phagocytosis) and out of the cell.

Cytoplasm- the internal semi-liquid environment of the cell, which provides communication between the nucleus and organelles located in it. The main processes of vital activity take place in the cytoplasm.

Cell organelles:

1) endoplasmic reticulum (ER)- a system of branching tubules, involved in the synthesis of proteins, lipids and carbohydrates, in the transport of substances in the cell;

2) ribosomes- bodies containing rRNA are located on the ER and in the cytoplasm, and are involved in protein synthesis. EPS and ribosomes are a single apparatus for protein synthesis and transport;

3) mitochondria- "power stations" of the cell, delimited from the cytoplasm by two membranes. The inner one forms cristae (folds) that increase its surface. Enzymes on cristae accelerate the reactions of oxidation of organic substances and the synthesis of energy-rich ATP molecules;

4) golgi complex- a group of cavities delimited by a membrane from the cytoplasm, filled with proteins, fats and carbohydrates, which are either used in life processes or removed from the cell. The membranes of the complex carry out the synthesis of fats and carbohydrates;

5) lysosomes- bodies filled with enzymes accelerate the reactions of splitting proteins to amino acids, lipids to glycerol and fatty acids, polysaccharides to monosaccharides. In lysosomes, dead parts of the cell, whole cells and cells are destroyed.

Cell inclusions- Accumulations of spare nutrients: proteins, fats and carbohydrates.

Core- the most important part of the cell. It is covered with a double-membrane membrane with pores through which some substances penetrate into the nucleus, while others enter the cytoplasm. Chromosomes are the main structures of the nucleus, carriers of hereditary information about the characteristics of an organism. It is transmitted in the process of division of the mother cell to daughter cells, and with germ cells - to daughter organisms. The nucleus is the site of DNA, mRNA, rRNA synthesis.

Exercise:

Explain why organelles are called specialized structures of the cell?

Answer: organelles are called specialized cell structures, since they perform strictly defined functions, they are stored in the nucleus hereditary information, ATP is synthesized in mitochondria, photosynthesis proceeds in chloroplasts, etc.

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Organelles - constantly present in the cytoplasm, specialized to perform certain functions of the structure. According to the principle of organization, membrane and non-membrane cell organelles are distinguished.

Membrane cell organelles

1. Endoplasmic reticulum (EPS) - a system of internal membranes of the cytoplasm, forming large cavities - tanks and numerous tubules; occupies a central position in the cell, around the nucleus. EPS makes up to 50% of the volume of the cytoplasm. EPS channels connect all cytoplasmic organelles and open into the perinuclear space of the nuclear envelope. Thus, EPS is an intracellular circulatory system. There are two types of membranes of the endoplasmic reticulum - smooth and rough (granular). However, it must be understood that they are part of one continuous endoplasmic reticulum. Ribosomes are located on granular membranes, where protein synthesis takes place. Enzyme systems involved in the synthesis of fats and carbohydrates are ordered on smooth membranes.

2. The Golgi apparatus is a system of tanks, tubules and vesicles formed by smooth membranes. This structure is located on the cell periphery with respect to the EPS. On the membranes of the Golgi apparatus, the enzyme systems involved in the formation of more complex organic compounds from proteins, fats and carbohydrates synthesized in EPS. This is where membranes are assembled and lysosomes are formed. The membranes of the Golgi apparatus provide for the accumulation, concentration and packaging of the secret released from the cell.

3. Lysosomes are membrane organelles containing up to 40 proteolytic enzymes capable of breaking down organic molecules. Lysosomes are involved in the processes of intracellular digestion and apoptosis (programmed cell death).

4. Mitochondria - energy stations of the cell. Two-membrane organelles with a smooth outer and inner membrane, forming cristae - ridges. Enzyme systems involved in the synthesis of ATP are ordered on the inner surface of the inner membrane. Mitochondria contain a circular DNA molecule similar in structure to the chromosome of prokaryotes. There are many small ribosomes on which protein synthesis is partially independent of the nucleus. However, the genes contained in the circular DNA molecule are not enough to ensure all aspects of the life of mitochondria, and they are semi-autonomous structures of the cytoplasm. An increase in their number occurs due to division, which is preceded by the doubling of the circular DNA molecule.

5. Plastids - organelles characteristic of plant cells. There are leukoplasts - colorless plastids, chromoplasts with a red-orange color, and chloroplasts. - green plastids. All of them have a single structural plan and are formed by two membranes: the outer (smooth) and the inner, forming partitions - the thylakoids of the stroma. On the thylakoids of the stroma there are grana, consisting of flattened membrane vesicles - thylakoid grana, stacked one on top of the other like coin columns. Inside the thylakoids of the grana is chlorophyll. The light phase of photosynthesis takes place here - in the grains, and the reactions of the dark phase - in the stroma. Plastids have a ring-shaped DNA molecule, similar in structure to the prokaryotic chromosome, and many small ribosomes, on which protein synthesis is partially independent of the nucleus. Plastids can pass from one species to another (chloroplasts to chromoplasts and leukoplasts), they are semi-autonomous cell organelles. The increase in the number of plastids occurs due to their division in two and budding, which is preceded by the reduplication of the circular DNA molecule.

non-membrane cell organelles

1. Ribosomes - rounded formations of two subunits, consisting of 50% RNA and 50% proteins. Subunits are formed in the nucleus, in the nucleolus, and in the cytoplasm in the presence of Ca 2+ ions they combine into integral structures. In the cytoplasm, ribosomes are located on the membranes of the endoplasmic reticulum (granular ER) or freely. In the active center of ribosomes, the process of translation occurs (selection of tRNA anticodons to mRNA codons). Ribosomes, moving along the mRNA molecule from one end to the other, sequentially make mRNA codons available for contact with tRNA anticodons.

2. Centrioles (cell center) are cylindrical bodies, the walls of which are 9 triads of protein microtubules. In the cell center, the centrioles are located at right angles to each other. They are capable of self-reproduction on the principle of self-assembly. Self-assembly - the formation of structures similar to existing ones with the help of enzymes. Centrioles take part in the formation of spindle fibers. Provide the process of divergence of chromosomes during cell division.

3. Flagella and cilia - organelles of movement; they have a single structural plan - the outer part of the flagellum faces the environment and is covered with a section of the cytoplasmic membrane. They are a cylinder: its wall is 9 pairs of protein microtubules, and in the center there are two axial microtubules. At the base of the flagellum, located in the ectoplasm - the cytoplasm that lies directly under the cell membrane, another short microtubule is added to each pair of microtubules. As a result, a basal body is formed, consisting of nine triads of microtubules.

4. The cytoskeleton is represented by a system of protein fibers and microtubules. Provides maintenance and change in the shape of the cell body, the formation of pseudopodia. Responsible for amoeboid movement, forms the inner frame of the cell, ensures the movement of cellular structures through the cytoplasm.

At the dawn of the development of life on Earth, all cellular forms were represented by bacteria. They sucked organic matter dissolved in the primordial ocean through the surface of the body.

Over time, some bacteria adapted to produce organic substances from inorganic ones. To do this, they used the energy sunlight. The first ecological system emerged in which these organisms were producers. As a result, oxygen released by these organisms appeared in the Earth's atmosphere. With it, you can get much more energy from the same food, and use the additional energy to complicate the structure of the body: dividing the body into parts.

One of the important achievements of life is the separation of the nucleus and cytoplasm. The nucleus contains hereditary information. A special membrane around the core made it possible to protect against accidental damage. As necessary, the cytoplasm receives commands from the nucleus that direct the vital activity and development of the cell.

Organisms in which the nucleus is separated from the cytoplasm formed the super-kingdom of the nuclear (these include plants, fungi, animals).

Thus, the cell - the basis of the organization of plants and animals - arose and developed in the course of biological evolution.

Even with the naked eye, and even better under a magnifying glass, you can see that the pulp of a ripe watermelon consists of very small grains, or grains. These are cells - the smallest "bricks" that make up the bodies of all living organisms, including plants.

The life of a plant is carried out by the combined activity of its cells, creating a single whole. With the multicellularity of plant parts, there is a physiological differentiation of their functions, specialization of various cells depending on their location in the plant body.

A plant cell differs from an animal cell in that it has a dense shell that covers the inner contents from all sides. The cell is not flat (as it is usually portrayed), it most likely looks like a very small vial filled with slimy contents.

The structure and functions of a plant cell

Consider a cell as a structural and functional unit of an organism. Outside, the cell is covered with a dense cell wall, in which there are thinner sections - pores. Under it is a very thin film - a membrane that covers the contents of the cell - the cytoplasm. In the cytoplasm there are cavities - vacuoles filled with cell sap. In the center of the cell or near the cell wall is a dense body - the nucleus with the nucleolus. The nucleus is separated from the cytoplasm by the nuclear envelope. Small bodies, plastids, are distributed throughout the cytoplasm.

The structure of a plant cell

The structure and functions of plant cell organelles

Organoid	Drawing	Description	Function	Peculiarities
Cell wall or plasma membrane		Colourless, transparent and very durable	Passes into the cell and releases substances from the cell.	The cell membrane is semi-permeable
Cytoplasm		Thick viscous substance	It contains all other parts of the cell.	Is in constant motion
Nucleus (important part of the cell)		round or oval	Ensures the transfer of hereditary properties to daughter cells during division	Central part of the cell
		Spherical or irregular shape	Takes part in protein synthesis
		A reservoir separated from the cytoplasm by a membrane. Contains cell sap	Spare nutrients and waste products that are unnecessary to the cell accumulate.	As the cell grows, small vacuoles merge into one large (central) vacuole
plastids		Chloroplasts	Use the light energy of the sun and create organic from inorganic	The shape of discs separated from the cytoplasm by a double membrane
		Chromoplasts	Formed as a result of the accumulation of carotenoids	Yellow, orange or brown
		Leucoplasts	Colorless plastids
nuclear envelope		Consists of two membranes (outer and inner) with pores	Separates the nucleus from the cytoplasm	Enables exchange between nucleus and cytoplasm

The living part of the cell is a membrane-limited, ordered, structured system of biopolymers and internal membrane structures involved in the totality of metabolic and energy processes that maintain and reproduce the entire system as a whole.

An important feature is that there are no open membranes with free ends in the cell. Cell membranes always limit cavities or areas, closing them from all sides.

Modern generalized diagram of a plant cell

plasmalemma(outer cell membrane) - an ultramicroscopic film 7.5 nm thick., Consisting of proteins, phospholipids and water. This is a very elastic film that is well wetted by water and quickly restores integrity after damage. It has a universal structure, i.e. typical for all biological membranes. Plant cells outside the cell membrane have a strong cell wall that creates an external support and maintains the shape of the cell. It is made up of fiber (cellulose), a water-insoluble polysaccharide.

Plasmodesmata of a plant cell, are submicroscopic tubules penetrating the membranes and lined with a plasma membrane, which thus passes from one cell to another without interruption. With their help, intercellular circulation of solutions containing organic nutrients occurs. They also transmit biopotentials and other information.

Poromy called holes in the secondary membrane, where the cells are separated only by the primary membrane and the middle plate. The areas of the primary membrane and the middle plate that separate the adjacent pores of adjacent cells are called the pore membrane or the closing film of the pore. The closing film of the pore is pierced by plasmodesmenal tubules, but a through hole is usually not formed in the pores. Pores facilitate the transport of water and solutes from cell to cell. In the walls of neighboring cells, as a rule, one against the other, pores are formed.

Cell wall has a well-defined, relatively thick shell of a polysaccharide nature. The plant cell wall is a product of the cytoplasm. The Golgi apparatus and the endoplasmic reticulum take an active part in its formation.

The structure of the cell membrane

The basis of the cytoplasm is its matrix, or hyaloplasm, a complex colorless, optically transparent colloidal system capable of reversible transitions from sol to gel. The most important role of hyaloplasm is to unite all cellular structures into a single system and ensure interaction between them in the processes of cellular metabolism.

Hyaloplasm(or cytoplasmic matrix) is internal environment cells. It consists of water and various biopolymers (proteins, nucleic acids, polysaccharides, lipids), of which the main part is proteins of various chemical and functional specificities. The hyaloplasm also contains amino acids, monosugars, nucleotides and other low molecular weight substances.

Biopolymers form a colloidal medium with water, which, depending on the conditions, can be dense (in the form of a gel) or more liquid (in the form of a sol), both in the entire cytoplasm and in its individual sections. In the hyaloplasm, various organelles and inclusions are localized and interact with each other and with the environment of the hyaloplasm. Moreover, their location is most often specific to certain cell types. Through the bilipid membrane, the hyaloplasm interacts with the extracellular environment. Consequently, hyaloplasm is a dynamic environment and plays an important role in the functioning of individual organelles and the vital activity of cells as a whole.

Cytoplasmic formations - organelles

Organelles (organelles) - structural components cytoplasm. They have a certain shape and size, are mandatory cytoplasmic structures of the cell. In their absence or damage, the cell usually loses the ability to continue to exist. Many of the organelles are capable of division and self-reproduction. They are so small that they can only be seen with an electron microscope.

Core

The nucleus is the most visible and usually the largest organelle of the cell. It was first studied in detail by Robert Brown in 1831. The nucleus provides the most important metabolic and genetic functions of the cell. It is quite variable in shape: it can be spherical, oval, lobed, lenticular.

The nucleus plays a significant role in the life of the cell. A cell from which the nucleus has been removed no longer secretes a shell, stops growing and synthesizing substances. The products of decay and destruction intensify in it, as a result of which it quickly dies. The formation of a new nucleus from the cytoplasm does not occur. New nuclei are formed only by fission or crushing of the old one.

The internal content of the nucleus is karyolymph (nuclear juice), which fills the space between the structures of the nucleus. It contains one or more nucleoli, as well as a significant number of DNA molecules connected to specific proteins - histones.

The structure of the nucleus

nucleolus

The nucleolus, like the cytoplasm, contains mainly RNA and specific proteins. Its most important function is that the formation of ribosomes takes place in it, which carry out the synthesis of proteins in the cell.

golgi apparatus

The Golgi apparatus is an organoid that has a universal distribution in all types of eukaryotic cells. It is a multi-tiered system of flat membrane sacs, which thicken along the periphery and form vesicular processes. It is most often located near the nucleus.

golgi apparatus

The Golgi apparatus necessarily includes a system of small vesicles (vesicles), which are laced from thickened cisterns (discs) and are located along the periphery of this structure. These vesicles play the role of an intracellular transport system of specific sectoral granules and can serve as a source of cellular lysosomes.

The functions of the Golgi apparatus also consist in the accumulation, separation and release of intracellular synthesis products, decay products, and toxic substances outside the cell with the help of bubbles. The products of the synthetic activity of the cell, as well as various substances that enter the cell from the environment through the channels of the endoplasmic reticulum, are transported to the Golgi apparatus, accumulate in this organoid, and then enter the cytoplasm in the form of droplets or grains and are either used by the cell itself or excreted. . In plant cells, the Golgi apparatus contains enzymes for the synthesis of polysaccharides and the polysaccharide material itself, which is used to build the cell wall. It is believed that it is involved in the formation of vacuoles. The Golgi apparatus was named after the Italian scientist Camillo Golgi, who first discovered it in 1897.

Lysosomes

Lysosomes are small vesicles, limited by a membrane, the main function of which is the implementation of intracellular digestion. The use of the lysosomal apparatus occurs during the germination of the plant seed (hydrolysis of reserve nutrients).

The structure of the lysosome

microtubules

Microtubules are membrane, supramolecular structures consisting of protein globules arranged in spiral or straight rows. Microtubules perform a predominantly mechanical (motor) function, providing mobility and contractility of cell organelles. Located in the cytoplasm, they give the cell a certain shape and ensure the stability of the spatial arrangement of organelles. Microtubules facilitate the movement of organelles to locations determined by physiological needs cells. A significant number of these structures are located in the plasmalemma, near the cell membrane, where they are involved in the formation and orientation of cellulose microfibrils of plant cell membranes.

Microtubule structure

Vacuole

The vacuole is the most important component of plant cells. It is a kind of cavity (reservoir) in the mass of the cytoplasm, filled with an aqueous solution of mineral salts, amino acids, organic acids, pigments, carbohydrates and separated from the cytoplasm by a vacuolar membrane - the tonoplast.

The cytoplasm fills the entire internal cavity only in the youngest plant cells. With the growth of the cell, the spatial arrangement of the initially continuous mass of the cytoplasm changes significantly: small vacuoles filled with cell sap appear in it, and the entire mass becomes spongy. With further cell growth, individual vacuoles merge, pushing the cytoplasmic layers to the periphery, as a result of which there is usually one large vacuole in the formed cell, and the cytoplasm with all organelles are located near the membrane.

water soluble organic and mineral compounds vacuoles determine the corresponding osmotic properties of living cells. This solution of a certain concentration is a kind of osmotic pump for controlled penetration into the cell and the release of water, ions and metabolite molecules from it.

In combination with the cytoplasm layer and its membranes, which are characterized by semipermeability properties, the vacuole forms an effective osmotic system. Osmotically determined are such indicators of living plant cells as osmotic potential, suction force and turgor pressure.

The structure of the vacuole

plastids

Plastids are the largest (after the nucleus) cytoplasmic organelles, inherent only in plant cells. They are not found only in fungi. Plastids play an important role in metabolism. They are separated from the cytoplasm by a double membrane membrane, and some of their types have a well-developed and ordered system of internal membranes. All plastids are of the same origin.

Chloroplasts- the most common and most functionally important plastids of photoautotrophic organisms that carry out photosynthetic processes that ultimately lead to the formation of organic substances and the release of free oxygen. Chloroplasts of higher plants have a complex internal structure.

The structure of the chloroplast

The sizes of chloroplasts in different plants are not the same, but on average their diameter is 4-6 microns. Chloroplasts are able to move under the influence of the movement of the cytoplasm. In addition, under the influence of illumination, an active movement of amoeboid-type chloroplasts to the light source is observed.

Chlorophyll is the main substance of chloroplasts. Thanks to chlorophyll, green plants are able to use light energy.

Leucoplasts(colorless plastids) are clearly marked bodies of the cytoplasm. Their sizes are somewhat smaller than the sizes of chloroplasts. More uniform and their shape, approaching the spherical.

The structure of the leucoplast

They are found in the cells of the epidermis, tubers, rhizomes. When illuminated, they very quickly turn into chloroplasts with a corresponding change in the internal structure. Leucoplasts contain enzymes, with the help of which starch is synthesized from excess glucose formed during photosynthesis, the bulk of which is deposited in storage tissues or organs (tubers, rhizomes, seeds) in the form of starch grains. In some plants, fats are deposited in leukoplasts. The reserve function of leukoplasts occasionally manifests itself in the formation of storage proteins in the form of crystals or amorphous inclusions.

Chromoplasts in most cases they are derivatives of chloroplasts, occasionally - leukoplasts.

The structure of the chromoplast

Ripening of rose hips, peppers, tomatoes is accompanied by the transformation of chloro- or leukoplasts of pulp cells into carotenoids. The latter contain predominantly yellow plastid pigments - carotenoids, which, upon maturation, are intensively synthesized in them, forming colored lipid drops, solid globules or crystals. Chlorophyll is destroyed.

Mitochondria

Mitochondria are organelles found in most plant cells. They have a variable shape of sticks, grains, threads. They were discovered in 1894 by R. Altman using a light microscope, and the internal structure was later studied using an electronic one.

The structure of the mitochondria

Mitochondria have a two-membrane structure. The outer membrane is smooth, the inner one forms outgrowths of various shapes - tubules in plant cells. The space inside the mitochondria is filled with semi-liquid content (matrix), which includes enzymes, proteins, lipids, calcium and magnesium salts, vitamins, as well as RNA, DNA and ribosomes. The mitochondrial enzyme complex accelerates the work of a complex and interconnected mechanism of biochemical reactions, as a result of which ATP is formed. In these organelles, cells are provided with energy - energy conversion chemical bonds nutrients into macroergic bonds of ATP during cellular respiration. It is in the mitochondria that the enzymatic breakdown of carbohydrates, fatty acids, amino acids occurs with the release of energy and its subsequent conversion into ATP energy. The accumulated energy is spent on growth processes, on new syntheses, etc. Mitochondria reproduce by division and live for about 10 days, after which they are destroyed.

Endoplasmic reticulum

Endoplasmic reticulum - a network of channels, tubules, vesicles, cisterns located inside the cytoplasm. Opened in 1945 by the English scientist K. Porter, it is a system of membranes with an ultramicroscopic structure.

The structure of the endoplasmic reticulum

The entire network is integrated into a single whole with the outer cell membrane of the nuclear envelope. Distinguish ER smooth and rough, carrying ribosomes. On the membranes of the smooth EPS there are enzyme systems involved in fat and carbohydrate metabolism. This type of membrane prevails in seed cells rich in reserve substances (proteins, carbohydrates, oils), ribosomes are attached to the membrane of the granular ER, and during the synthesis of a protein molecule, the polypeptide chain with ribosomes is immersed in the ER channel. The functions of the endoplasmic reticulum are very diverse: the transport of substances both inside the cell and between neighboring cells; division of a cell into separate sections in which various physiological processes and chemical reactions take place simultaneously.

Ribosomes

Ribosomes are non-membrane cellular organelles. Each ribosome consists of two unequal-sized particles and can be divided into two fragments that continue to retain the ability to synthesize protein after combining into a whole ribosome.

The structure of the ribosome

Ribosomes are synthesized in the nucleus, then leave it, passing into the cytoplasm, where they are attached to the outer surface of the membranes of the endoplasmic reticulum or are located freely. Depending on the type of protein synthesized, ribosomes can function alone or combine into complexes - polyribosomes.

A cell is a single living system consisting of two inextricably linked parts - the cytoplasm and the nucleus (color table XII).

Cytoplasm- this is an internal semi-liquid environment in which the nucleus and all organelles of the cell are located. It has a fine-grained structure, penetrated by numerous thin threads. It contains water, dissolved salts and organic matter. The main function of the cytoplasm is to unite and ensure the interaction of the nucleus and all organelles of the cell.

outer membrane surrounds the cell with a thin film consisting of two layers of protein, between which there is a fatty layer. It is permeated with numerous small pores through which ions and molecules are exchanged between the cell and the environment. The membrane thickness is 7.5-10 nm, the pore diameter is 0.8-1 nm. In plants, a fiber sheath forms on top of it. The main functions of the outer membrane are to limit the internal environment of the cell, protect it from damage, regulate the flow of ions and molecules, remove metabolic products and synthesized substances (secrets), connect cells and tissues (due to outgrowths and folds). The outer membrane ensures the penetration of large particles into the cell by phagocytosis (see sections in "Zoology" - "Protozoa", in "Anatomy" - "Blood"). In a similar way, the cell absorbs liquid drops - pinocytosis (from the Greek "pino" - I drink).

Endoplasmic reticulum(EPS) is composed of membranes a complex system channels and cavities penetrating the entire cytoplasm. EPS is of two types - granular (rough) and smooth. On the membranes of the granular network there are many tiny bodies - ribosomes; they do not exist in a smooth network. The main function of EPS is participation in the synthesis, accumulation and transportation of the main organic substances produced by the cell. Protein is synthesized in granular ER, while carbohydrates and fats are synthesized in smooth ER.

Ribosomes- small bodies, 15-20 nm in diameter, consisting of two particles. There are hundreds of thousands of them in every cell. Most ribosomes are located on the membranes of the granular ER, and some are located in the cytoplasm. They are composed of proteins and rRNA. The main function of ribosomes is protein synthesis.

Mitochondria- these are small bodies, 0.2-0.7 microns in size. Their number in a cell reaches several thousand. They often change shape, size and location in the cytoplasm, moving to their most active part. The outer cover of the mitochondria consists of two three-layer membranes. The outer membrane is smooth, the inner one forms numerous outgrowths on which respiratory enzymes are located. The internal cavity of mitochondria is filled with fluid, which houses ribosomes, DNA and RNA. New mitochondria are formed when old ones divide. The main function of mitochondria is the synthesis of ATP. They synthesize a small amount of proteins, DNA and RNA.

plastids unique to plant cells. There are three types of plastids - chloroplasts, chromoplasts and leukoplasts. They are capable of mutual transition into each other. Plastids reproduce by division.

Chloroplasts(60) have green color, oval shape. Their size is 4-6 microns. From the surface, each chloroplast is bounded by two three-layer membranes - outer and inner. Inside it is filled with a liquid, in which there are several dozens of special, interconnected cylindrical structures - gran, as well as ribosomes, DNA and RNA. Each grana consists of several tens of flat membrane sacs superimposed on each other. On the transverse section, it has a rounded shape, its diameter is 1 µm. All the chlorophyll is concentrated in the grains, and the process of photosynthesis takes place in them. The resulting carbohydrates first accumulate in the chloroplast, then enter the cytoplasm, and from it to other parts of the plant.

Chromoplasts determine the red, orange and yellow color of flowers, fruits and autumn leaves. They have the form of polyhedral crystals located in the cytoplasm of the cell.

Leucoplasts colorless. They are found in unpainted parts of plants (stems, tubers, roots), have a round or rod-shaped shape (5-6 microns in size). They store reserves.

Cell Center found in animal and lower plant cells. It consists of two small cylinders - centrioles (about 1 micron in diameter) located perpendicular to each other. Their walls consist of short tubes, the cavity is filled with a semi-liquid substance. Their main role is the formation of the division spindle and the uniform distribution of chromosomes among daughter cells.

Golgi complex was named after the Italian scientist who first discovered it in nerve cells. It has a diverse shape and consists of cavities limited by membranes, tubules extending from them and bubbles located at their ends. The main function is the accumulation and excretion of organic substances synthesized in the endoplasmic reticulum, the formation of lysosomes.

Lysosomes- rounded little bodies with a diameter of about 1 micron. From the surface, the lysosome is limited by a three-layer membrane, inside it there is a complex of enzymes that can break down carbohydrates, fats and proteins. There are several dozen lysosomes in a cell. New lysosomes are formed in the Golgi complex. Their main function is to digest food that has entered the cell by phagocytosis and remove dead organelles.

Organelles of movement- flagella and cilia - are cell outgrowths and have the same structure in animals and plants (their common origin). The movement of multicellular animals is provided by muscle contractions. The main structural unit of a muscle cell is myofibrils - thin threads more than 1 cm long, 1 micron in diameter, arranged in bundles along the muscle fiber.

Cell inclusions- Carbohydrates, fats and proteins - are non-permanent components of the cell. They are periodically synthesized, accumulated in the cytoplasm as reserve substances and used in the course of the life of the organism.

Carbohydrates are concentrated in grains of starch (in plants) and glycogen (in animals). There are many of them in liver cells, potato tubers and other organs. Fats accumulate in the form of droplets in plant seeds, subcutaneous tissue, connective tissue, etc. Proteins are deposited in the form of grains in animal eggs, plant seeds, and other organs.

Core one of the most important organelles in the cell. It is separated from the cytoplasm by the nuclear membrane, consisting of two three-layer membranes, between which there is a narrow strip of semi-liquid substance. Through the pores of the nuclear envelope, the exchange of substances between the nucleus and the cytoplasm takes place. The cavity of the nucleus is filled with nuclear juice. It contains the nucleolus (one or more), chromosomes, DNA, RNA, proteins and carbohydrates. The nucleolus is a rounded body ranging in size from 1 to 10 microns or more; it synthesizes RNA. Chromosomes are only visible in dividing cells. In the interphase (non-dividing) nucleus, they are present in the form of thin long filaments of chromatin (DNA-to-protein connections). They contain hereditary information. The number and shape of chromosomes in each species of animals and plants are strictly defined. Somatic cells that make up all organs and tissues contain a diploid (double) set of chromosomes (2 n); germ cells (gametes) - haploid (single) set of chromosomes (n). The diploid set of chromosomes in the nucleus of a somatic cell is created from paired (identical), homologous chromosomes. Chromosomes of different pairs (non-homologous) differ from each other in shape, location centromeres And secondary stretches.

prokaryotes- These are organisms with small, primitively arranged cells, without a clearly defined nucleus. These include blue-green algae, bacteria, phages and viruses. Viruses are DNA or RNA molecules covered with a protein coat. They are so small that they can only be seen with an electron microscope. They lack cytoplasm, mitochondria and ribosomes, so they are not able to synthesize the protein and energy necessary for their life. Once in a living cell and using other people's organic matter and energy, they develop normally.

eukaryotes- organisms with larger typical cells containing all the main organelles: nucleus, endoplasmic reticulum, mitochondria, ribosomes, Golgi complex, lysosomes and others. Eukaryotes include all other plant and animal organisms. Their cells have a similar type of structure, which convincingly proves the unity of their origin.

Organelles – permanent and mandatory components of cells; specialized sections of the cytoplasm of a cell that have a specific structure and perform specific functions in the cell. Distinguish between organelles of general and special purpose.

Organelles general purpose are present in most cells (endoplasmic reticulum, mitochondria, plastids, Golgi complex, lysosomes, vacuoles, cell center, ribosomes). Special purpose organelles are characteristic only of specialized cells (myofibrils, flagella, cilia, contractile and digestive vacuoles). Organelles (with the exception of ribosomes and the cell center) have a membrane structure.

Endoplasmic reticulum(EPR) – this is a branched system of interconnected cavities, tubules and channels formed by elementary membranes and penetrating the entire thickness of the cell. Opened in 1943 by Porter. There are especially many channels of the endoplasmic reticulum in cells with intensive metabolism. On average, the volume of EPS is from 30% to 50% of the total cell volume. EPS is labile. Form of internal lacunae and cana

catches, their size, location in the cell and number change in the process of life. The cell is more developed in animals. EPS is morphologically and functionally related to boundary layer cytoplasm, nuclear membrane, ribosomes, the Golgi complex, vacuoles, forming together with them a single functional and structural system for the exchange of substances and energy and the movement of substances inside the cell. Mitochondria and plastids accumulate near the endoplasmic reticulum.

There are two types of EPS: rough and smooth. On the membranes of the smooth (agranular) ER, enzymes of the fat and carbohydrate synthesis systems are localized: carbohydrates and almost all cellular lipids are synthesized here. Membranes of a smooth variety of the endoplasmic reticulum predominate in the cells of the sebaceous glands, liver (glycogen synthesis), and in cells with a high content of nutrients (plant seeds). Ribosomes are located on the membrane of the rough (granular) EPS, where protein biosynthesis takes place. Some of the proteins synthesized by them are included in the membrane of the endoplasmic reticulum, the rest enter the lumen of its channels, where they are converted and transported to the Golgi complex. Especially a lot of rough membranes in the cells of the glands and nerve cells.

Rice. Rough and smooth endoplasmic reticulum.

Rice. Transport of substances through the system nucleus - endoplasmic reticulum (EPR) - Golgi complex.

Functions of the endoplasmic reticulum:

1) synthesis of proteins (rough ER), carbohydrates and lipids (smooth ER);

2) transport of substances, both entering the cell and newly synthesized;

3) division of the cytoplasm into compartments (compartments), which ensures the spatial separation of enzyme systems necessary for their sequential entry into biochemical reactions.

Mitochondria - are present in almost all cell types of unicellular and multicellular organisms (with the exception of mammalian erythrocytes). Their number in different cells varies and depends on the level of functional activity of the cell. There are about 2500 of them in the rat liver cell, and 20-22 in the male reproductive cell of some mollusks. There are more of them in the pectoral muscle of flying birds than in the pectoral muscle of non-flying birds.

Mitochondria are shaped like spherical, oval and cylindrical bodies. The sizes are 0.2 - 1.0 microns in diameter and up to 5 - 7 microns in length.

Rice. Mitochondria.

The length of filamentous forms reaches 15-20 microns. Outside, mitochondria are bounded by a smooth outer membrane, similar in composition to the plasmalemma. The inner membrane forms numerous outgrowths - cristae - and contains numerous enzymes, ATP-somes (mushroom bodies), involved in the transformation of nutrient energy into ATP energy. The number of cristae depends on the function of the cell. There are a lot of cristae in mitochondria; they occupy the entire internal cavity of the organoid. In mitochondria of embryonic cells, cristae are single. In plants, outgrowths of the inner membrane are more often tubular. The mitochondrial cavity is filled with a matrix that contains water, mineral salts, enzyme proteins, and amino acids. Mitochondria have an autonomous protein-synthesizing system: a circular DNA molecule, various types of RNA, and smaller ribosomes than in the cytoplasm.

Mitochondria are closely connected by membranes of the endoplasmic reticulum, whose channels often open directly into the mitochondria. With an increase in the load on the organ and intensification of synthetic processes that require energy expenditure, the contacts between EPS and mitochondria become especially numerous. The number of mitochondria can rapidly increase by fission. The ability of mitochondria to reproduce is due to the presence of a DNA molecule in them, resembling the circular chromosome of bacteria.

Mitochondrial Functions:

1) synthesis of a universal energy source - ATP;

2) synthesis of steroid hormones;

3) biosynthesis of specific proteins.

plastids - organelles of a membrane structure, characteristic only for plant cells. They are involved in the synthesis of carbohydrates, proteins and fats. According to the content of pigments, they are divided into three groups: chloroplasts, chromoplasts and leukoplasts.

Chloroplasts have a relatively constant elliptical or lenticular shape. The size of the largest diameter is 4 - 10 microns. The number in a cell ranges from a few units to several tens. Their size, color intensity, number and location in the cell depend on the lighting conditions, the type and physiological state of the plants.

Rice. Chloroplast, structure.

These are protein-lipoid bodies, consisting of 35-55% protein, 20-30% lipids, 9% chlorophyll, 4-5% carotenoids, 2-4% nucleic acids. The amount of carbohydrates varies; a certain amount of mineral substances Chlorophyll was found - an ester of an organic dibasic acid - chlorophyllin and organic alcohols - methyl (CH 3 OH) and phytol (C 20 H 39 OH). In higher plants, chlorophyll a is constantly present in chloroplasts - has a blue-green color, and chlorophyll b - yellow-green; and the content of chlorophyll, and several times more.

In addition to chlorophyll, chloroplasts contain pigments - carotene C 40 H 56 and xanthophyll C 40 H 56 O 2 and some other pigments (carotenoids). In a green leaf, the yellow satellites of chlorophyll are masked by a brighter green color. However, in autumn, during leaf fall, in most plants, chlorophyll is destroyed and then the presence of carotenoids in the leaf is detected - the leaf turns yellow.

The chloroplast is surrounded by a double membrane consisting of an outer and an inner membrane. The internal contents - the stroma - has a lamellar (lamellar) structure. In the colorless stroma, grana are isolated - green-colored bodies, 0.3 - 1.7 microns. They are a collection of thylakoids - closed bodies in the form of flat vesicles or discs of membrane origin. Chlorophyll in the form of a monomolecular layer is located between the protein and lipid layers in close connection with them. Spatial arrangement pigment molecules in the membrane structures of chloroplasts is very appropriate and creates optimal conditions for the most efficient absorption, transmission and use of radiant energy. Lipids form anhydrous dielectric layers of chloroplast membranes necessary for the functioning of the electron transport chain. The role of links in the electron transport chain is performed by proteins (cytochromes, plastoquinones, ferredoxin, plastocyanin) and individual chemical elements - iron, manganese, etc. The number of grains in the chloroplast is from 20 to 200. Stroma lamellae are located between the grains, connecting them with each other. The gran lamellae and stroma lamellae have a membranous structure.

The internal structure of the chloroplast makes possible the spatial dissociation of numerous and varied reactions, which in their totality constitute the content of photosynthesis.

Chloroplasts, like mitochondria, contain specific RNA and DNA, as well as smaller ribosomes and the entire molecular arsenal necessary for protein biosynthesis. These organelles have a sufficient amount of i-RNA to ensure the maximum activity of the protein-synthesizing system. However, they also contain enough DNA to encode certain proteins. They reproduce by division, by simple constriction.

It has been established that chloroplasts can change their shape, size and position in the cell, that is, they are able to move independently (chloroplast taxis). They found two types of contractile proteins, due to which, obviously, the active movement of these organelles in the cytoplasm is carried out.

Chromoplasts are widely distributed in the generative organs of plants. They color the petals of flowers (buttercup, dahlia, sunflower), fruits (tomatoes, mountain ash, wild rose) in yellow, orange, red. In vegetative organs, chromoplasts are much less common.

The color of chromoplasts is due to the presence of carotenoids - carotene, xanthophyll and lycopene, which are in plastids in a different state: in the form of crystals, a lipoid solution, or in combination with proteins.

Chromoplasts, in comparison with chloroplasts, have a simpler structure - they lack a lamellar structure. The chemical composition is also different: pigments - 20-50%, lipids up to 50%, proteins - about 20%, RNA - 2-3%. This indicates a lower physiological activity of chloroplasts.

Leucoplasts do not contain pigments, they are colorless. These smallest plastids are round, ovoid or rod-shaped. In the cell, they often cluster around the nucleus.

Internally, the structure is even less differentiated compared to chloroplasts. They synthesize starch, fats, proteins. In accordance with this, three types of leukoplasts are distinguished - amyloplasts (starch), oleoplasts ( vegetable oils) and proteoplasts (proteins).

Leukoplasts arise from proplastids, with which they are similar in shape and structure, but differ only in size.

All plastids are genetically related to each other. They are formed from proplastids - the smallest colorless cytoplasmic formations similar in appearance with mitochondria. Proplastids are found in spores, eggs, in embryonic cells of growth points. Chloroplasts (in the light) and leukoplasts (in the dark) are formed directly from proplastids, and chromoplasts develop from them, which are the end product in the evolution of plastids in the cell.

Golgi complex - was first discovered in 1898 by the Italian scientist Golgi in animal cells. This is a system of internal cavities, cisterns (5-20), located close and parallel to each other, and large and small vacuoles. All these formations have a membrane structure and are specialized sections of the endoplasmic reticulum. In animal cells, the Golgi complex is better developed than in plant cells; in the latter it is called dictyosomes.

Rice. The structure of the Golgi complex.

Proteins and lipids that enter the lamellar complex undergo various transformations, accumulate, sort, pack into secretory vesicles and are transported according to their destination: to various structures inside the cell or outside the cell. The membranes of the Golgi complex also synthesize polysaccharides and form lysosomes. In the cells of the mammary glands, the Golgi complex is involved in the formation of milk, and in the cells of the liver - bile.

Functions of the Golgi complex:

1) concentration, dehydration and compaction of proteins synthesized in the cell, fats, polysaccharides and substances that came from outside;

2) the assembly of complex complexes of organic substances and their preparation for removal from the cell (cellulose and hemicellulose in plants, glycoproteins and glycolipids in animals);

3) synthesis of polysaccharides;

4) formation of primary lysosomes.

Lysosomes - small oval bodies with a diameter of 0.2-2.0 microns. The central position is occupied by a vacuole containing 40 (according to various sources, 30-60) hydrolytic enzymes capable of breaking down proteins, nucleic acids, polysaccharides, lipids and other substances in an acidic environment (pH 4.5-5).

Around this cavity is a stroma, dressed on the outside with an elementary membrane. The breakdown of substances with the help of enzymes is called lysis, so the organelle is called a lysosome. Lysosomes are formed in the Golgi complex. Primary lysosomes approach directly pinocytic or phagocytic vacuoles (endosomes) and pour their contents into their cavity, forming secondary lysosomes (phagosomes), inside which digestion of substances occurs. The products of lysis through the membrane of lysosomes enter the cytoplasm and are included in further metabolism. Secondary lysosomes with remnants of undigested substances are called residual bodies. An example of secondary lysosomes are the digestive vacuoles of protozoa.

Functions of lysosomes:

1) intracellular digestion of food macromolecules and foreign components entering the cell during pino- and phagocytosis, providing the cell with additional raw materials for biochemical and energy processes;

2) during starvation, lysosomes digest some organelles and replenish the supply of nutrients for a while;

3) destruction of temporary organs of embryos and larvae (tail and gills in a frog) in the process of postembryonic development;

Rice. Lysosome formation

Vacuoles – fluid-filled cavities in the cytoplasm of plant cells and protists. They have the form of bubbles, thin tubules and another. Vacuoles are formed from extensions of the endoplasmic reticulum and vesicles of the Golgi complex as the thinnest cavities, then, as the cell grows and the accumulation of metabolic products, their volume increases and the number decreases. A developed, formed cell usually has one large vacuole, which occupies a central position.

The vacuoles of plant cells are filled with cell sap, which is water solution organic (malic, oxalic, citric acids, sugars, inulin, amino acids, proteins, tannins, alkaloids, glucosides) and mineral (nitrates, chlorides, phosphates) substances.

Protists have digestive and contractile vacuoles.

Functions of vacuoles:

1) storage of reserve nutrients and receptacles for excretions (in plants);

2) determine and maintain osmotic pressure in cells;

3) provide intracellular digestion in protists.

Rice. Cell center.

Cell Center usually located near the nucleus and consists of two centrioles located perpendicular to each other and surrounded by a radiant sphere. Each centriole is a hollow cylindrical body 0.3-0.5 µm long and 0.15 µm long, the wall of which is formed by 9 triplets of microtubules. If the centriole lies at the base of the cilium or flagellum, then it is called basal body.

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

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

The centrosome is characteristic of animal cells, some fungi, algae, mosses, and ferns.

Functions of the cell center:

1) the formation of fission poles and the formation of fission spindle microtubules.

Ribosomes - small spherical organelles, from 15 to 35 nm. Consist of two subunits large (60S) and small (40S). They contain about 60% protein and 40% ribosomal RNA. rRNA molecules form its structural framework. Most proteins are specifically associated with certain regions of rRNA. Some proteins are only incorporated into ribosomes during protein synthesis. Ribosome subunits are formed in the nucleolus. and through the pores in the nuclear membrane enter the cytoplasm, where they are located either on the EPA membrane, or on the outer side of the nuclear membrane, or freely in the cytoplasm. First, rRNAs are synthesized on nucleolar DNA, which are then covered with ribosomal proteins coming from the cytoplasm, cleaved to the right sizes and form ribosome subunits. There are no fully formed ribosomes in the nucleus. The association of subunits into a whole ribosome occurs in the cytoplasm, as a rule, during protein biosynthesis. Compared with mitochondria, plastids, prokaryotic cells, ribosomes in the cytoplasm of eukaryotic cells are larger. They can combine 5-70 units into polysomes.

Ribosome functions:

1) participation in protein biosynthesis.

Rice. 287. Ribosome: 1 - small subunit; 2 - large subunit.

Cilia, flagella – outgrowths of the cytoplasm covered with an elementary membrane, under which there are 20 microtubules, forming 9 pairs along the periphery and two single ones in the center. At the base of the cilia and flagella are the basal bodies. The flagella are up to 100 µm long. Cilia are short - 10-20 microns - flagella. The movement of the flagella is helical, and that of the cilia is paddle-like. Thanks to cilia and flagella, bacteria, protists, ciliates move, particles or liquids move (cilia of the ciliated epithelium of the respiratory tract, oviducts), germ cells (spermatozoa).

Rice. The structure of flagella and cilia in eukaryotes

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

In functional terms, inclusions are either compounds temporarily removed from the metabolism of cells (reserve substances - starch grains, lipid drops and protein deposits), or end products of metabolism (crystals of certain substances).

starch grains. These are the most common plant cell inclusions. Starch is stored in plants exclusively in the form of starch grains. They are formed only in the plastid stroma of living cells. During photosynthesis, green leaves produce assimilation, or primary starch. Assimilation starch does not accumulate in the leaves and, rapidly hydrolyzing to sugars, flows into the parts of the plant in which it accumulates. There it turns back into starch, which is called secondary. Secondary starch is also formed directly in tubers, rhizomes, seeds, that is, where it is deposited in stock. Then they call him spare. Leukoplasts that store starch are called amyloplasts. Especially rich in starch are seeds, underground shoots (tubers, bulbs, rhizomes), parenchyma of conductive tissues of roots and stems of woody plants.

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

Lipid drops, as a rule, accumulate directly in the hyaloplasm. They are spherical bodies usually of submicroscopic size. Lipid droplets can also accumulate in leukoplasts, which are called elaioplasts.

Protein inclusions are formed in various cell organelles in the form of amorphous or crystalline deposits various forms and buildings. Most often, crystals can be found in the nucleus - in the nucleoplasm, sometimes in the perinuclear space, less often in the hyaloplasm, plastid stroma, in the extensions of the EPR tanks, the matrix of peroxisomes and mitochondria. Vacuoles contain both crystalline and amorphous protein inclusions. IN most protein crystals are found in the storage cells of dry seeds in the form of so-called aleuronic 3 grains or protein bodies.

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