Cell cytoplasm composition. Specific features of the structure of the cytoplasm of plant cells

Cytoplasm - the contents of a cell outside the nucleus, enclosed in a plasma membrane. It has a transparent color and a gel-like consistency. The cytoplasm consists mainly of water, and also contains enzymes, salts, and various organic molecules.

Cytoplasmic function

The cytoplasm functions to support and suspend organelles and cellular molecules. Many cellular processes also take place in the cytoplasm.

Some of these processes involve protein synthesis, the first stage known as glycolysis, and. In addition, the cytoplasm helps move substances such as hormones around the cell and also dissolves cellular waste.

Components of the cytoplasm

Organelles

Organelles are tiny cellular structures that perform specific functions within the cell. Examples of organelles include:, and.

Also within the cytoplasm is a network of fibers that help the cell maintain its shape and provide support for the organelles.

Cytoplasmic inclusions

Cytoplasmic inclusions are particles temporarily suspended in the cytoplasm. Inclusions are composed of macromolecules and granules.

The three types of inclusions found in the cytoplasm are secretory and nutrient inclusions, as well as pigment granules. Examples of secretory inclusions are proteins, enzymes and acids. Glycogen (storage of glucose molecules) and lipids are examples of nutrient inclusions. Melanin present in skin cells is an example of the inclusion of pigment granules.

Cytoplasmic divisions

The cytoplasm can be divided into two main parts: endoplasm and ectoplasm. The endoplasm is the central region of the cytoplasm that contains organelles. Ectoplasm is a more gel-like peripheral part of the cell cytoplasm.

Cell membrane

The cell or plasma membrane is a structure that prevents the shedding of cytoplasm from the cell. This membrane consists of phospholipids that form a lipid bilayer that separates the contents of the cell from the extracellular fluid. The lipid bilayer is semipermeable, which means that only a few molecules are able to diffuse across the membrane to enter or exit the cell. Extracellular fluid, proteins, lipids and other molecules can be added to the cytoplasm of the cell using. In this process, molecules and extracellular fluid are internalized when the membrane forms a vesicle.

The vesicle separates fluid, molecules and kidneys from the cell membrane, forming an endosome. The endosome moves within the cell to deliver its contents to their respective destinations. Substances are removed from the cytoplasm by. In this process, vesicles budded from the Golgi bodies merge with the cell membrane, displacing their contents from the cell. The plasma membrane also provides structural support for the cell, acting as a stable platform for the attachment of the cytoskeleton and.

The cytoplasm is perhaps the most important part of any cellular structure, which is a kind of "connective tissue" between all the constituents of the cell.

The functions and properties of the cytoplasm are diverse, its role in ensuring the vital activity of the cell can hardly be overestimated.

This article describes most of the processes occurring in the smallest living structure at the macrolevel, where the main role is assigned to a gel-like mass that fills the internal volume of the cell and gives the latter its appearance and shape.

In contact with

The cytoplasm is a viscous (jelly-like) transparent substance that fills every cell and is limited by the cell membrane. It contains water, salts, proteins and other organic molecules.

All eukaryotic organelles, such as the nucleus, endoplasmic reticulum, and mitochondria, are located in the cytoplasm. The part of it that is not contained in the organelles is called cytosol. Although it may seem that the cytoplasm has neither shape nor structure, in fact it is a highly organized substance, which is provided by the so-called cytoskeleton (protein structure). The cytoplasm was discovered in 1835 by Robert Brown and other scientists.

Chemical composition

Mainly the cytoplasm is the substance that fills the cell. This viscous, gel-like substance is 80% water and is usually clear and colorless.

Cytoplasm is the substance of life, which is also called molecular soup, in which cellular organelles are suspended and connected to each other by a bilayer lipid membrane. The cytoskeleton in the cytoplasm gives it its shape. The process of cytoplasmic flow ensures the movement of nutrients between organelles and the removal of waste products. This substance contains many salts and is a good conductor of electricity.

As it was said, the substance consists of 70-90% water and is colorless... Most of the cellular processes occur in it, for example, glycose, metabolism, cell division processes. The outer transparent glassy layer is called ectoplasm or cell cortex, the inner part of the substance is called endoplasm. In plant cells, the process of cytoplasmic flow takes place, which is the flow of the cytoplasm around the vacuole.

Main characteristics

The following properties of the cytoplasm should be listed:

Structure and components

In prokaryotes (such as bacteria), which do not have a nucleus attached to a membrane, the cytoplasm represents the entire contents of the cell within the plasma membrane. In eukaryotes (for example, plant and animal cells), the cytoplasm is formed by three distinct components: cytosol, organelles, various particles and granules, called cytoplasmic inclusions.

Cytosol, organelles, inclusions

Cytosalt is a semi-liquid component located externally in relation to the nucleus and inside the plasma membrane. Cytosalt makes up approximately 70% of the cell volume and consists of water, cytoskeleton fibers, salts, and organic and inorganic molecules dissolved in water. Also contains proteins and soluble structures such as ribosomes and proteasomes. The inner part of the cytosol, the most fluid and granular, is called the endoplasm.

The fiber network and high concentrations of dissolved macromolecules, such as proteins, lead to the formation of macromolecular clusters, which strongly affect the transport of substances between cytoplasmic components.

Organoid means "small organ" that is associated with a membrane. Organoids are found within the cell and perform specific functions necessary to sustain this smallest building block of life. Organoids are small cellular structures with specialized functions. Examples include:

• mitochondria;
• ribosomes;
• core;
• lysosomes;
• chloroplasts (in plants);
• endoplasmic reticulum;
• Golgi apparatus.

The cell also contains the cytoskeleton, a network of fibers that help it maintain its shape.

Cytoplasmic inclusions are particles that are temporarily suspended in a jelly-like substance and consist of macromolecules and granules. You can find three types of such inclusions: secretory, nutritive, pigmented. Examples of secretory inclusions include proteins, enzymes, and acids. Glycogen (a molecule for storing glucose) and lipids are prime examples of nutrient inclusions, melanin found in skin cells is an example of pigment inclusions.

Cytoplasmic inclusions, being small particles suspended in the cytosol, represent a diverse range of inclusions present in different types of cells. These can be either crystals of calcium oxalate or silicon dioxide in plants, or granules of starch and glycogen. A wide range of inclusions are spherical lipids, present in both prokaryotes and eukaryotes, and serving to accumulate fats and fatty acids. For example, such inclusions occupy most of the volume of adiposites - specialized storage cells.

Functions of the cytoplasm in the cell

The most important functions can be summarized in the following table:

• ensuring the shape of the cell;
• habitat of organelles;
• transport of substances;
• stock of nutrients.

The cytoplasm serves to support organelles and cell molecules. Many cellular processes take place in the cytoplasm. Some of these processes include protein synthesis, the first stage of cellular respiration which bears the name glycolysis, processes of mitosis and meiosis... In addition, the cytoplasm helps hormones move through the cell, and waste products are also removed through it.

Most of the different actions and events take place in this gelatin-like liquid, which contains enzymes that contribute to the decomposition of waste products, and many metabolic processes take place here. The cytoplasm provides the cell with a form, filling it, helps to maintain the organelles in their places. Without it, the cell would look "deflated", and various substances could not easily move from one organoid to another.

Transport of substances

The liquid substance of the contents of the cell is very important for the maintenance of its vital functions, since allows for easy exchange of nutrients between organelles... This exchange is due to the process of cytoplasmic flow, which is the flow of cytosol (the most mobile and fluid part of the cytoplasm), which carry nutrients, genetic information and other substances from one organoid to another.

Some of the processes that take place in the cytosol also include metabolite transport... The organoid can produce amino acids, fatty acids and other substances, which are transported through the cytosalt to the organoid that needs these substances.

Cytoplasmic flows lead to the fact that the cell itself can move... Some of the smallest vital structures have cilia (small, hair-like formations on the outside of the cell that allow the cell to move through space). For other cells, for example, amoeba, the only way to move is the movement of fluid in the cytosol.

Supply of nutrients

In addition to transporting various materials, the liquid space between organelles acts as a kind of storage chamber for these materials until the moment when they are really needed by one or another organelle. Proteins, oxygen and various building blocks are suspended inside the cytosol. In addition to useful substances, the cytoplasm also contains metabolic products that wait in turn until the removal process removes them from the cell.

Plasma membrane

Cellular, or plasma, membrane is a formation that prevents the flow of cytoplasm from the cell. This membrane consists of phospholepids, which form a double lipid layer, which is semipermeable: only certain molecules can penetrate this layer. Proteins, lipids and other molecules can penetrate the cell membrane through the process of endocytosis, in which a vesicle of these substances is formed.

The bubble, which includes fluid and molecules, breaks off from the membrane, forming an endosome. The latter moves inside the cell to its addressees. Waste products are excreted through the process of exocytosis. In this process, the bubbles formed in the Golgi apparatus are combined with a membrane, which pushes their contents into the environment. Also, the membrane provides the cell's shape and serves as a supporting platform for the cytoskeleton and cell wall (in plants).

Plant and animal cells

The similarity of the internal contents of the cells of plants and animals indicates their identical origin. The cytoplasm provides mechanical support to the internal structures of the cell, which are suspended in it.

The cytoplasm maintains the shape and consistency of the cell, and also contains many chemicals that are key to maintaining life and metabolism.

Metabolic reactions such as glycose and protein synthesis occur in the jelly-like content. In plant cells, unlike animals, there is a movement of the cytoplasm around the vacuole, which is known as the cytoplasmic flow.

The cytoplasm of animal cells is a substance similar to a gel dissolved in water, it fills the entire volume of the cell and contains proteins and other important molecules necessary for life. The gel-like mass contains proteins, hydrocarbons, salts, sugars, amino acids and nucleotides, all cellular organelles and the cytoskeleton.

Cytoplasm (from the Greek kytos - cell and plasma - formed) is the content of a plant or animal cell, with the exception of the nucleus (karyoplasm). The cytoplasm and karyoplasm are called protoplasm. In an ordinary microscope, it looks like a semi-liquid substance (basic substance, or hyaloplasm), in which various droplets, vacuoles, granules, rod-shaped or filamentous structures are suspended. Under an electron microscope, the cytoplasm has an even more complex appearance (a whole labyrinth of membranes with protoplasm enclosed between them). The cytoplasm is a complex mixture of colloidal proteins, fats, and other organic compounds. Of inorganic compounds, water is present in the cytoplasm, as well as various mineral substances.

Outside, each cell is surrounded by the thinnest plasma membrane (i.e., envelope), which plays an important role in regulating the composition of the cellular content and is a derivative of the cytoplasm. The membrane is a three-layer structure (the outer and inner layers consist of protein, between them there is a layer of phospholipid molecules) with a total thickness of about 120 Å (angstroms). The cell wall is permeated with tiny holes - pores through which the protoplasm of one cell can exchange with the protoplasm of other, neighboring cells.

Various organelles are located in the cytoplasm - specialized structures that perform specific functions in the life of cells. Among them, mitochondria play the most important role in metabolism; in an ordinary microscope, they are visible in the form of small rods or grains. The data indicate their complex structure. Each mitochondrion has a membrane consisting of three layers and an internal cavity. Numerous partitions protrude from the shell into this cavity filled with liquid contents, which do not reach the opposite wall, called cristae. Respiratory processes are associated with mitochondria. The cytoplasm contains the so-called endoplasmic reticulum (reticulum) - a branched system of submicroscopic tubules, tubules and cisterns bounded by membranes. The membranes of the endoplasmic reticulum are double. On the side facing the main substance of the cytoplasm, on each membrane there are numerous granules, which include ribonucleic acid, in accordance with which they became known as ribosomes. With the participation of ribosomes in the endoplasmic reticulum, protein synthesis occurs.

One of the components of the cytoplasm is the mesh apparatus or "Golgi complex", which is closely associated with the endoplasmic reticulum and is involved in the processes of secretion. There is data showing that the membranes of the cell nucleus (see) without interruption pass into the membranes of the endoplasmic reticulum and the Golgi complex. In the cytoplasm of some animal cells, fibrils - thin filamentous formations and tubules, which are contractile elements, may be present. Often, grains of glycogen (in plants - starch), fatty substances in the form of small drops and other structures are visible in the cytoplasm. See also Cage.

Cytoplasm (from the Greek kytos - cell and plasma - something molded, formed) - the contents of the cell, with the exception of the nucleus (karyoplasm). The cytoplasm and karyoplasm are called protoplasm. Sometimes the term "protoplasm" is incorrectly used in the narrow sense of the word to designate the extra-nuclear part of the cell, but in this sense it is more expedient to leave the term "cytoplasm". In physical and chemical terms, the cytoplasm is a multiphase colloidal system. The dispersion medium of the cytoplasm is water (up to 80%). The dispersed phase contains protein and fatty substances that form aggregates of molecules - micelles. Cytoplasm is a viscous liquid, almost colorless, with a specific gravity of about 1.04, often strongly refracting light, as a result of which it is visible under a microscope even in unstained cells.

A characteristic feature of the cytoplasm, which determines its biological properties, is the instability of colloids, the ability to rapidly alternate states of gelatinization and liquefaction. This circumstance explains the variety of pictures of the structure of the cytoplasm (granular, filamentous, reticular, etc.) described by different researchers. Depending on the age of the cell, its physiological state, function, etc., a different structure of the cytoplasm can be observed. The nature of the pretreatment (especially histological fixation) used to obtain the preparation is also of great importance. The morphology of the cytoplasm depends on the state of its colloids.

About 60 biogenic elements are found in the cytoplasm; its most important chemical components are proteins, carbohydrates, lipoids and a number of salts. The defining difference between the cytoplasm and the nucleus is the presence of a significant amount of ribonucleic acid (RNA).

The cytoplasm contains enzymes of carbohydrate and protein metabolism and others that regulate the energy of the cell. In an optical microscope, the cytoplasm is most often represented as a homogeneous or poorly structured colloidal mass, in which, in addition to the nucleus, organelles (organelles) and inclusions are located. Organoids are obligatory (or, at least, constantly occurring in certain categories of cells) components of the cytoplasm that perform a specific function and have a specific structure that best suits the performance of this function. Organoids include mitochondria, the Golgi apparatus, the cell center, plastids of plant cells, etc. Inclusions are temporary formations associated with one or another stage of cellular metabolism (secretion, deposition of waste substances, plastic and energy reserve substances, etc.). The most widespread are the inclusions of neutral fats and glycogen. The cytoplasm is stained with acidic dyes, and then two zones are clearly detected in it - the central one, which has a low viscosity and contains a significant number of inclusions (endoplasm), and the peripheral one with high density and the absence of inclusions (ectoplasm). The most peripheral layer of ectoplasm (surface, or cortical) has a number of important properties that ensure the processes of chemical and physical interaction between the cell and the environment. In the cytoplasm of some cells (secretory, salivary and pancreas, hematopoietic), sharply basophilic areas are found - ergastoplasm.

A significant change in views on the structure of the cytoplasm occurred in connection with the use of an electron microscope. It turned out that the cytoplasm consists of a basic substance (matrix, hyaloplasm), which contains two other important components - the endoplasmic reticulum and ribosomes, as well as organelles and inclusions. Hyaloplasm is a liquid or semi-liquid continuous phase between the denser components of the cytoplasm. Hyaloplasm is homogeneous or fine-grained, but sometimes fibrillar components (so-called structural proteins) are found in it, which create some stability of this part of the cytoplasm and explain its properties such as elasticity, contractility, stability (rigidity), etc. The viscosity of the cytoplasm of even cells of the same type is different: in the eggs of the sea urchin, it is equal to 3 cps, and in the Paramecia ciliates, it is 8000 cps.

The endoplasmic reticulum (so named because it was first described in the inner parts of the cell) is a system of double membranes, between which there are spaces that form tubules, vesicles and dilated cavities - cisterns. The endoplasmic reticulum, which forms the so-called vacuolar system of the cell, connects the surface membrane of the cell, the cytoplasm, mitochondria and the nuclear membrane into one whole. Due to the existence of such a connection, continuous metabolic exchange is possible between all parts of the cell.

On the outer surface of the endoplasmic membranes of basophilic territories (ergastoplasm), there are numerous ribosomes (granular type of the endoplasmic reticulum); the smooth type of this organelle is characteristic of areas in which the synthesis of fats and carbohydrates occurs. The endoplasmic reticulum is found in all cells (except for mature erythrocytes of mammals), but it is poorly developed in undifferentiated (for example, embryonic) cells and is most strongly developed in actively metabolizing cells. Ribosomes are granules with a diameter of 150-350 Å. - an essential component of the cytoplasm. In the most primitively constructed cells, they are located freely in the hyaloplasm, in more highly organized cells, as a rule, they are associated with the endoplasmic reticulum. Ribosomes contain amino acids and RNA. The thread of the latter connects them into active complexes called polyribosomes. The main function of these organelles is the synthesis of a specific protein, a process in which the so-called messenger RNA plays a decisive role.

The cell membrane - the surface area of ​​the cytoplasm - has a thickness of 70-120 Å and consists of one lipoid and two protein layers; it is the existence of this shell that determines the selective permeability of the cell for a number of substances. The surface area of ​​the cytoplasm carries out the initial stages of the processes of phagocytosis (see), i.e., the capture of solids, and pinocytosis (cm), the ingestion of liquids, which is of decisive importance with the active penetration of these substances into the cell or the protective capture of pathogens (bacteria, protozoa). In the cytoplasm, in some cases, the process of their neutralization occurs, and in others (for example, with a viral infection), on the contrary, their reproduction.

Cytoplasm is a carrier of hereditary units that determine the properties of an organism that can be transmitted to offspring (cytoplasmic heredity). Correns (S. Correns) was the first to show that variegation and defects of chlorophyll formation in plants depend on the presence and distribution of colorless and colored organelles - plastids, responsible for the formation of organic substances in the plant cell from water and carbon dioxide with the help of sunlight. Thus, certain hereditary traits are transmitted through the cytoplasm. The phenomena of cytoplasmic heredity, first described in plants, were then discovered in a variety of organisms. So, V. Ephrussi showed that, acting with acridine compounds, you can get a small hereditary yeast race. Its appearance is obviously associated with a change in mitochondria. Drosophila with cytoplasmic inheritance transmitted through the ovum is associated with different sensitivity to the action of CO 2. Finally, the antigenic properties of animal and human cells, transmitted from one generation to another, are also determined, apparently, by cytoplasmic heredity. However, it should not be assumed that the properties of the cytoplasm, including its participation in the inheritance of traits, are isolated from the properties of the rest of the constituent parts of the cell, primarily the nucleus. Due to the existence of a single vacuolar-membrane system, there is a continuous connection that ensures the exchange of various materials between all components of the cell. It is especially enhanced during certain periods of the cell's life. So, in the process of division, nuclear matter and cytoplasm are mixed and the mitotic apparatus is formed from the resulting mixoplasm (see Mitosis).

The processes of protein synthesis in the cytoplasm begin with the exit from the nucleus of messenger RNA (see. Nucleic acids).

Lesson objectives:

• To deepen the general understanding of the structure of the eukaryotic cell.
• Formulate knowledge about the properties and functions of the cytoplasm.
• In practical work, make sure that the cytoplasm of a living cell is elastic and semi-permeable.

During the classes

• We write down the topic of the lesson.
• We repeat the passed material, we work with tests.
• We read and comment on test questions. (Cm. Annex 1).
• We write down homework: p.5.2., Entries in notebooks.
• Learning new material.

This is the main substance of the cytoplasm.

It is a complex colloidal system.

Consists of water, proteins, carbohydrates, nucleic acids, lipids, inorganic substances.

There is a cytoskeleton.

The cytoplasm moves all the time.

Cytoplasmic functions.

• The internal environment of the cell.
• It unites all cellular structures.
• Determines the location of the organelles.
• Provides intracellular transport.

Cytoplasm properties:

• Elasticity.
• Semi-permeability.

Thanks to these properties, the cell undergoes temporary dehydration and maintains the constancy of its composition.

It is necessary to remember such concepts as turgor, osmosis, diffusion.

In order to get acquainted with the properties of the cytoplasm, students are invited to perform practical work: "Study of plasmolysis and deplasmolysis in a plant cell. (See Appendix 2).

In the process, you need to draw a cell of the skin of the onion (Point 1. The cell in points 2 and 3).

Make a conclusion about the processes taking place in the cell (orally)

The guys are trying to explain what is observed in point 2 plasmolysis separation of the parietal layer of the cytoplasm, in point 3 there is deplasmolysis- return of the cytoplasm to a normal state.

It is necessary to explain the reasons for these phenomena. To relieve difficulties before lessons, I give three students teaching aids: "Biological Encyclopedic Dictionary", Volume 2 of Biology N. Green, "Experiment on Plant Physiology" E.M. Vasiliev, where they independently find material about the causes plasmolysis and deplasmolysis.

It turns out that the cytoplasm is elastic and semi-permeable. If it were permeable, then the concentration of cell juice and hypertonic solution would be equalized by diffuse movement of water and solutes from the cell to the solution and back. However, the cytoplasm, possessing the property of semi-permeability, does not allow substances dissolved in water to enter the cell.

On the contrary, only water, according to the laws of osmosis, will be sucked out of the cell by the hypertonic solution, i.e. move through the semipermeable cytoplasm. The volume of the vacuole will decrease. The cytoplasm, due to its elasticity, follows the contracting vacuole and lags behind the cell membrane. This is how it goes plasmolysis.

When a plasmolyzed cell is immersed in water, deplasmolysis is observed.

Generalization of the knowledge gained in the lesson.

1. What functions are inherent in the cytoplasm?
2. Properties of the cytoplasm.
3. The importance of plasmolysis and deplasmolysis.
4. Cytoplasm is
   a) an aqueous solution of salts and organic substances together with the organelles of the cell, but without the nucleus;
   b) a solution of organic substances, including the cell nucleus;
   c) an aqueous solution of mineral substances, including all organelles of the cell with a nucleus.
5. What is the name of the main substance of the cytoplasm?

During practical work, the teacher checks the correctness of its implementation. Those who succeed can give marks. Grades are given for correct conclusions.