What is the cytoplasm briefly. Specific features of the structure of the cytoplasm of plant cells

Separated from the environment by the plasmalemma, it includes the main substance (matrix and hyaloplasm), the obligatory cellular components in it - organelles, as well as various non-permanent structures - inclusions.

In an electron microscope, the cytoplasmic matrix looks like a homogeneous or fine-grained substance with a low electron density. The main substance of the cytoplasm fills the space between the plasmalemma, the nuclear membrane and other intracellular structures. Hyaloplasm is a complex colloidal system that includes various biopolymers. The main substance of the cytoplasm forms the true internal environment of the cell, which unites all intracellular structures and ensures their interaction with each other.

In an electron microscope, the cytoplasmic matrix looks like a homogeneous or fine-grained substance with a low electron density. It includes a microtrabecular network formed by thin fibrils 2-3 nm thick and penetrating the entire cytoplasm. The main substance of the cytoplasm should be considered in the same way as a complex colloidal system capable of moving from a liquid state to a gel-like one.

Functions:

It unites all cellular structures and ensures their interaction with each other.

It is a reservoir for enzymes and ATP.

Spare products are put aside.

Various reactions (protein synthesis) take place.

The constancy of the environment.

It is a framework.

Inclusions are called non-permanent components of the cytoplasm, which serve as reserve nutrients, products to be removed from the cell, and ballast substances.

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

Non-membrane organelles:

1) Ribosomes- small mushroom-shaped bodies in which protein synthesis takes place. They consist of ribosomal RNA and a protein that forms a large and small subunit.

2) cytoskeleton- the musculoskeletal system of the cell, including non-membrane formations that perform both frame and motor functions in the cell. These filamentous or fibrillar-nye can quickly appear and just as quickly disappear. This system includes fibrillar structures (5-7nm) and microtubules (they consist of 13 subunits).

3) The cell center consists of centrioles (150 nm long, 300-500 nm in diameter) surrounded by centrospheres.

Centrioles are made up of 9 triplets of microtubules. Functions:

The formation of mitotic spindle filaments.

Ensuring the separation of sister chromatids in the anaphase of mitosis.

4) Cilia (A cilia is a thin cylindrical outgrowth of the cytoplasm with a constant diameter of 300 nm. This outgrowth is covered with a plasma membrane from the base to its very top) and flagella (150 microns long) are special movement organelles found in some cells of various organisms .

What is cytoplasm? What is its structure and composition? What functions does it perform? In this article, we will answer all these questions in detail. In addition, we will consider the structural features of the cytoplasm and its properties, as well as talk about the division of the structure of cell membranes and the most important cell organelles.

Structural units of all tissues and organs of the cell. Two types of their structural organization

Cells are known to form the tissues of all plants and animals. These structural units of all living things can vary in shape, size, and even internal structure. But at the same time, they have similar principles in the processes of life, including metabolism, growth and development, irritability and variability. The simplest forms of life consist of a single cell and reproduce by division.
Scientists have identified two types of organization of the cellular structure:

• prokaryotic;
• eukaryotic.

They have many differences in their structure. There is no structurally designed core. Its only chromosome is located directly in the cytoplasm, that is, it does not separate from other elements in any way. This structure is characteristic of bacteria. Their cytoplasm is poor in composition of structures, but it contains small ribosomes. The eukaryotic cell is much more complex than the prokaryotic cell. Its DNA, associated with a protein, is located in chromosomes located in a separate cell organoid - the nucleus. It is separated from other cell organelles by a porous membrane and consists of such elements as: chromatin, nuclear juice and nucleolus. Nevertheless, there is something in common between the two types of cellular organization. Both prokaryotes and eukaryotes have a shell. And their internal contents are represented by a special colloidal solution, in which there are various organelles and temporary inclusions.

cytoplasm. Its composition and functions

So let's get to the heart of our research. What is cytoplasm? Let's take a closer look at this cellular formation. The cytoplasm is an archival component of the cell, located between the nucleus and the plasma membrane. Semi-liquid, it is permeated with tubules, microtubules, microfilaments and filaments. Also, cytoplasm can be understood as a colloidal solution, which is characterized by the movement of colloidal particles and other components. In this semi-liquid medium, consisting of water, various organic and inorganic compounds, there are cellular structures-organelles, as well as temporary inclusions. The most important functions of the cytoplasm are as follows. It carries out the design of all cellular components into a single system. Due to the presence of tubules and microtubules, the cytoplasm performs the function of the cell skeleton and provides an environment for the implementation of physiological and biochemical processes. In addition, it enables the functioning of all cellular organelles and provides movement. These functions of the cytoplasmic cell are extremely important, as they allow the structural unit of all living things to carry out their normal vital activity. Now you know what cytoplasm is. They are also aware of what position it occupies in the cell and what “work” it performs. Next, we consider the composition and structure of the colloidal solution in more detail.

Are there differences in the cytoplasm of plant and animal cells?

Membrane organelles in a colloidal solution are considered to be the endoplasmic reticulum, mitochondria, lysosomes, plastids, and the outer cytoplasmic membrane. In the cells of animals and plants, the composition of the semi-liquid medium is different. The cytoplasm has special organelles - plastids. They are specific protein bodies that differ in function, shape and are stained with pigments in different colors. Plastids are located in the cytoplasm and are able to move with it. They grow, multiply and produce organic compounds containing enzymes. The cytoplasm in a plant cell has three types of plastids. Yellowish or orange ones are called chromoplasts, green ones are called chloroplasts, and colorless ones are called leucoplasts. There is another characteristic feature - the Golgi complex is represented by dictyosomes scattered throughout the cytoplasm. Animal cells, unlike plant cells, have two layers of cytoplasm. The outer one is called ectoplasm, and the inner one is called endoplasm. The first layer is adjacent to the cell membrane, and the second is located between it and the porous nuclear membrane. Ectoplasm contains a large amount of microfilament - filaments from the molecules of the globular actin protein. Endoplasm contains various organelles, granules and is characterized by lower viscosity.

Hyaloplasm in a eukaryotic cell

The basis of the cytoplasm of eukaryotes is the so-called hyaloplasm. It is a slimy, colorless, heterogeneous solution in which metabolic processes are constantly taking place. Hyaloplasm (in other words, the matrix) is with a complex structure. It includes soluble RNA and proteins, lipids and polysaccharides. The hyaloplasm also contains a significant amount of nucleotides, amino acids, as well as ions of inorganic compounds such as Na - or Ca 2+.

The matrix does not have a homogeneous structure. It comes in two forms called gel (solid) and sol (liquid). There are transitions between them. In the liquid phase there is a system of the thinnest protein filaments, which are called microtrabeculae. They bind all structures within the cell. And in the places of their intersection there are groups of ribosomes. Microtrabeculae together with microtubules and microfilaments form the cytoplasmic skeleton. It determines and arranges the location of all cell organelles.

Organic and inorganic substances in the colloidal solution of the cell

Let's consider what is the chemical composition of the cytoplasm? Substances contained in the cell can be classified into two groups - organic and inorganic. The first is represented by proteins, carbohydrates, fats and nucleic acids. Carbohydrates in the cytoplasm are represented by mono-, di- and polysaccharides. Monosaccharides, colorless crystalline substances, usually sweet in taste, include fructose, glucose, ribose, etc. Large polysaccharide molecules are composed of monosaccharides. In the cell, they are represented by starch, glycogen and cellulose. Lipids, that is, fat molecules, are formed by residues of glycerol and fatty acids. The structure of the cytoplasm: inorganic substances are represented primarily by water, which, as a rule, is up to 90% of the mass. It performs important functions in the cytoplasm.

Water is a universal solvent, gives elasticity, is directly involved in the movement of substances both inside and between cells. As for the macroelements that form the basis of biopolymers, more than 98% of the entire composition of the cytoplasm is occupied by oxygen, hydrogen, carbon and nitrogen. In addition to them, the cell contains sodium, calcium, sulfur, magnesium, chlorine, etc. Mineral salts are in the form of anions and cations, while their ratio determines the acidity of the environment.

Properties of a colloidal solution in a cell

Consider further what are the main properties of the cytoplasm. First, it is a constant cyclosis. It represents the intracellular movement of the cytoplasm. It was first recorded and described in the 18th century by the Italian scientist Corti. Cyclosis occurs throughout the protoplasm, including the strands that connect the cytoplasm with the nucleus. If the movement stops for any reason, the eukaryotic cell dies. The cytoplasm is necessarily in constant cyclosis, which is detected by the movement of organelles. The speed of matrix movement depends on various factors, including light and temperature. For example, in the epidermis of onion scales, the cyclosis rate is about 6 m/s. The movement of the cytoplasm in a plant organism has a huge impact on its growth and development, facilitating the transport of substances between cells. The second important property is the viscosity of the colloidal solution. It varies greatly depending on the type of organism. In some living beings, the viscosity of the cytoplasm can be very slightly higher than in others, on the contrary, it can reach the viscosity of glycerol. It is believed that it depends on the metabolism. The more intense the exchange, the lower the viscosity of the colloidal solution becomes.

Another important property is semipermeability. The cytoplasm in its composition has boundary membranes. They, due to their special structure, have the ability to selectively pass molecules of some substances and not pass others. The cytoplasm plays an essential role in the life process. It is not constant throughout life, changes with age and increases in plant organisms with increasing light intensity and temperature. It is difficult to overestimate the importance of the cytoplasm. It is involved in energy metabolism, nutrient transport, and the elimination of exotoxins. Also, the matrix is ​​considered an osmotic barrier and is involved in the regulation of the processes of development, growth and cell division. The cytoplasm plays an important role in DNA replication.

Features of cell reproduction

All plant and animal cells reproduce by division. Three types are known - indirect, direct and reduction. The first is otherwise called amitosis. Indirect reproduction occurs as follows. Initially, the nucleus is “laced up”, and then the division of the cytoplasm occurs. As a result, two cells are formed, which gradually grow to the size of the mother. This type of division in animals is extremely rare. As a rule, they have an indirect division, that is, mitosis. It is much more complicated than amitosis and is characterized by the fact that there is an increase in synthesis in the nucleus and a doubling of the amount of DNA. Mitosis has four phases called prophase, metaphase, anaphase, and telophase.

• The first phase is characterized by the formation of a ball of chromatin threads in place of the nucleus, and subsequently chromosomes in the form of "hairpins". During this period, the centrioles diverge to the poles and the formation of the achromatin spindle of division occurs.
• The second stage of mitosis is characterized by the fact that the chromosomes, reaching maximum spiralization, begin to settle down on the equator of the cell in an orderly manner.
• In the third phase, the chromosome splits into two chromatids. In this case, the spindle threads contract and pull the daughter chromosomes to opposite poles.
• In the fourth phase of mitosis, disspiralization of chromosomes occurs, as well as the formation of a nuclear membrane around them. At the same time, the division of the cytoplasm occurs. Daughter cells have a diploid set of chromosomes.

Reduction division is characteristic exclusively of germ cells. With this type of cell reproduction, the formation of paired formations from chromosomes occurs. The exception is one unpaired chromosome. As a result of reduction division in two daughter cells, a half chromosome set is obtained. Unpaired is located in only one child cell. Sex cells that have a half set of chromosomes, mature and capable of fertilization, are called female and male gametes.

The concept of the cytoplasmic membrane

All animal cells, plants and even the simplest bacteria have a special surface apparatus that limits and protects the matrix from the external environment. The cytoplasmic membrane (plasmalemma, cell membrane, plasma membrane) is a selectively permeable layer of molecules (proteins, phospholipids) that encloses the cytoplasm. It includes three subsystems:

• plasma membrane;
• supramembrane complex;
• submembrane musculoskeletal apparatus of hyaloplasm.

The structure of the cytoplasmic membrane is as follows: it contains two layers of lipid molecules (bilayer), while each such molecule has a tail and a head. The tails are facing each other. They are hydrophobic. The heads are hydrophilic and face in and out of the cell. Protein molecules are included in the bilayer. Moreover, it is asymmetric, and different lipids are located in the monolayers. For example, in a eukaryotic cell, cholesterol molecules are located in the inner half of the membrane adjacent to the cytoplasm. Glycolipids are located exclusively in the outer layer, and their carbohydrate chains are always directed outward. The cytoplasmic membrane performs the most important functions, including limiting the internal contents of the cell from the external environment, allowing certain substances (glucose, amino acids) to penetrate into the cell. The plasmalemma carries out the transfer of substances into the cell, as well as their output to the outside, that is, excretion. Water, ions and small molecules of substances penetrate through the pores, and large solid particles are transported into the cell by phagocytosis. On the surface, the membrane forms microvilli, protrusions and protrusions, which allows not only to effectively absorb and release substances, but also to connect with other cells. The membrane provides the ability to attach a "unit of all living things" to various surfaces and promotes movement.

Organelles in the cytoplasm. Endoplasmic reticulum and ribosomes

In addition to hyaloplasm, the cytoplasm also contains many microscopic organelles that differ in structure. Their presence in plant and animal cells indicates that they all perform the most important functions and are vital. To some extent, these morphological formations are comparable to the organs of the human or animal body, which made it possible to call them organelles. In the cytoplasm, organelles visible under a light microscope are distinguished - a lamellar complex, mitochondria and a centrosome. Using an electron microscope, microtubules, lysosomes, ribosomes and the plasma reticulum are found in the matrix. The cytoplasm of the cell is permeated with various channels, which are called the "endoplasmic network". Their membrane walls are in contact with all other organelles and form a single system that carries out energy metabolism, as well as the movement of substances inside the cell. In the walls of these channels are ribosomes that look like tiny granules. They can be located singly or in groups. Ribosomes are composed of almost equal amounts of ribonucleic acid and proteins. Magnesium is also included in their composition. Ribosomes can not only be located in the EPS channels, but also lie freely in the cytoplasm, and also occur in the nucleus, where they are formed. The collection of channels containing ribosomes is called the granular endoplasmic reticulum. In addition to ribosomes, they contain enzymes that promote the synthesis of carbohydrates and fats. In the internal cavities of the channels are the waste products of the cell. Sometimes vacuoles are formed in the extensions of the EPS - and limited by the membrane. These organelles maintain turgor pressure. Lysosomes are small, oval-shaped formations. They are scattered throughout the cytoplasm. Lysosomes are formed in the EPS or the Golgi complex, where they are filled with hydrolytic enzymes. Lysosomes are designed to digest particles that have entered the cell due to phagocytosis.

Cytoplasm: structure and functions of its organelles. Golgi lamellar complex, mitochondria and centrosome

The Golgi complex is represented in plant cells by separate bodies, decorated with membranes, and in animals - by tubules, vesicles and cisterns. This organoid is intended for chemical change, compaction and subsequent release of cellular secretion products into the cytoplasm. It also carries out the synthesis of polysaccharides and the formation of glycoproteins. Mitochondria are rod-shaped, filamentous, or granular bodies. They are limited to two membranes, which consist of double layers of phospholipids and proteins. Cristae extend from the inner membranes of these organelles, on the walls of which there are enzymes. With their help, adenosine triphosphate (ATP) is synthesized. Mitochondria are sometimes referred to as the "cellular powerhouses" since they supply a significant proportion of adenosine triphosphate. It is used by the cell as a source of chemical energy. In addition, mitochondria perform other functions, including: signaling, cell necrosis, cell differentiation. The centrosome (cell center) consists of two centrioles, which are located at an angle to each other. This organoid is present in all animals and plants (except for protozoa and lower fungi) and is responsible for determining the poles during mitosis. In a dividing cell, the centrosome divides first. In this case, an achromatin spindle is formed, which sets the landmarks for chromosomes diverging towards the poles. In addition to the designated organelles, the cell may also contain special-purpose organelles, for example, cilia and flagella. Also, at certain stages of life, it may contain inclusions, that is, temporary elements. For example, nutrients such as fat droplets, proteins, starch, glycogen, etc.

Lymphocytes are the most important cells of the immune system

Lymphocytes are important cells belonging to the group of human and animal blood leukocytes and are involved in immunological reactions. They are divided by size and structural features into three subgroups:

• small - less than 8 microns in diameter;
• medium - with a diameter of 8 to 11 microns;
• large - with a diameter of over 11 microns.

Small lymphocytes predominate in the blood of animals. They have a large rounded nucleus, which prevails over the volume of the cytoplasm. The cytoplasm of lymphocytes of this subgroup looks like a nuclear rim or sickle adjacent to either side of the nucleus. Often the matrix contains some small azurophilic granules. Mitochondria, elements of the lamellar complex, and ER tubules are not numerous and are located near the nuclear depression. Medium and large lymphocytes are arranged somewhat differently. Their nuclei are bean-shaped, contain a smaller amount of condensed chromatin. It is easy to distinguish the nucleolus in them. The cytoplasm of lymphocytes of the second and third groups has a wider rim. There are two classes of lymphocytes, the so-called B- and T-lymphocytes. The first are formed in animals in the myeloid tissue of the bone marrow. These cells have the ability to form immunoglobulins. With their help, B-lymphocytes interact with antigens, recognizing the latter. T-lymphocytes are formed from bone marrow cells in the thymus (in its cortical part of the lobules). In their cytoplasmic membrane there are surface histocompatibility antigens, as well as numerous receptors, with the help of which foreign particles are recognized. Small lymphocytes are mainly represented by T-lymphocytes (more than 70%), among which there are a large number of long-lived cells. The vast majority of B-lymphocytes do not live long - from one week to a month.

We hope our article was useful, and now you know what cytoplasm, hyaloplasm and plasmalemma are. They are also aware of the functions, structure and significance of these cell formations for the life of the organism.

The structure of the cytoplasm

The interior of the cell is divided into cytoplasm and nucleus. The cytoplasm is the bulk of the cell.

Definition 1

Cytoplasm- this is the internal semi-liquid colloidal environment of the cell, separated from the external environment by the cell membrane, in which the nucleus, all organelles of the membrane and non-membrane structure are located.

The entire space between the organelles in the cell is filled with the soluble contents of the cytoplasm ( cytosol). The aggregate state of the cytoplasm can be different: rare - sol and viscous gel. The chemical composition of the cytoplasm is quite complex. This is a semi-liquid mucous colorless mass of a complex physico-chemical structure (biological colloid).

Animal cells and very young plant cells are completely filled with cytoplasm. In plant cells, during differentiation, small vacuoles are formed, in the process of merging of which a central vacuole is formed, and the cytoplasm moves to the membrane and lines it with a continuous layer.

The cytoplasm contains:

• salt (1%),
• sugar (4-6%),
• amino acids and proteins (10-12%),
• fats and lipids (2-3%) enzymes,
• up to 80% water.

All these substances form a colloidal solution that does not mix with water or vacuolar content.

The cytoplasm contains:

• matrix (hyaloplasm),
• cytoskeleton,
• organelles,
• inclusions.

Hyaloplasm- colloidal colorless structure of the cell. It consists of soluble proteins, RNA, polysaccharides, lipids and cellular structures arranged in a certain way: membranes, organelles, inclusions.

cytoskeleton, or intracellular skeleton, - a system of protein formations, - microtubules and microfilaments - performs a supporting function in the cell, participates in changing the shape of the cell and its movement, provides a certain arrangement of enzymes in the cell.

Organelles- these are stable cellular structures that perform certain functions that ensure all the processes of the cell's vital activity (movement, respiration, nutrition, synthesis of organic compounds, their transport, preservation and transmission of hereditary information).

Eukaryotic organelles are divided into:

1. two-membrane (mitochondria, plastids);
2. single-membrane (endoplasmic reticulum, Golgi apparatus (complex), lysosomes, vacuoles);
3. non-membrane (flagella, cilia, pseudopodia, myofibrils).

Inclusions- temporary structures of the cell. These include reserve compounds and metabolic end products: grains of starch and glycogen, fat drops, salt crystals.

Functions and properties of the cytoplasm

The cytoplasmic content of the cell is able to move, which favors the optimal placement of organelles and, as a result, biochemical reactions proceed better, the release of metabolic products, etc.

In protozoa (amoeba), due to the movement of the cytoplasm, the main movement of cells in space is carried out.

Cytoplasm formed various external formations of the cell - flagella, cilia, surface outgrowths, which play an important role in the movement of cells and contribute to the connection of cells in tissues.

The cytoplasm is the matrix for all cellular elements, ensuring the interaction of all cellular structures, various chemical reactions take place in it, substances move through the cytoplasm in the cell, as well as from cell to cell.

Cytoplasm - the contents of the cell outside the nucleus, enclosed in the 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.

Function of the cytoplasm

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

Some of these processes include protein synthesis, the first step 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 inside 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 consist of macromolecules and granules.

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

Cytoplasmic divisions

Cytoplasm can be divided into two main parts: endoplasm and ectoplasm. Endoplasm is the central region of the cytoplasm that contains organelles. Ectoplasm is the more gel-like peripheral portion of the cell's cytoplasm.

cell membrane

The cell or plasma membrane is a structure that prevents the cytoplasm from spilling out of the cell. This membrane is composed of phospholipids that form a lipid bilayer that separates the contents of the cell from the extracellular fluid. The lipid bilayer is semi-permeable, meaning that only some 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 with the help of. In this process, molecules and extracellular fluid are internalized as 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 the appropriate destinations. Substances are removed from the cytoplasm by. In this process, vesicles budded from the Golgi bodies fuse with the cell membrane, forcing their contents out of the cell. The plasma membrane also provides structural support to the cell, acting as a stable platform for the attachment of the cytoskeleton and .

Cytoplasm (from the Greek kytos - cell and plasma - formed) is the contents of a plant or animal cell, with the exception of the nucleus (karyoplasm). Cytoplasm and karyoplasm are called protoplasm. In a conventional microscope, it looks like a semi-liquid substance (ground substance, or hyaloplasm), in which a variety of 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 the inorganic compounds in the cytoplasm, there is water, as well as various minerals.

Outside, each cell is surrounded by the thinnest plasma membrane (i.e., shell), which plays an important role in regulating the composition of cellular contents and is a derivative of the cytoplasm. The membrane is a three-layer structure (the outer and inner layers are composed of protein, between them is a layer of phospholipid molecules) with a total thickness of about 120 Å (angstrom). The cell wall is permeated with the smallest 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 certain functions in the life of cells. Among them, mitochondria play the most important role in metabolism; in a conventional microscope, they are visible in the form of small sticks or grains. The data points to their complex structure. Each mitochondrion has a shell 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. In the cytoplasm there is 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 are numerous granules, which include ribonucleic acid, in accordance with which they were called ribosomes. With the participation of ribosomes in the endoplasmic reticulum, protein synthesis occurs.

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

Cytoplasm (from the Greek kytos - cell and plasma - something fashioned, formed) - the contents of the cell, with the exception of the nucleus (karyoplasm). Cytoplasm and karyoplasm are called protoplasm. Sometimes the term "protoplasm" is incorrectly used in the narrow sense of the word to refer to the extranuclear part of the cell, but in this sense it is more appropriate to leave the term "cytoplasm". In physicochemical 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 approximately 1.04, often strongly refracting light, as a result of which it can be seen 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 quickly replace each other in states of gelatinization and liquefaction. This circumstance explains the variety of pictures of the structure of the cytoplasm (granular, filamentous, reticulate, 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. Of great importance is also the nature of the pre-treatment (especially the histological fixation) used in obtaining the drug. 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).

Enzymes of carbohydrate and protein metabolism and others regulating the energy of the cell are localized in the cytoplasm. In an optical microscope, the cytoplasm most often appears as a homogeneous or weakly structured colloidal mass, in which, in addition to the nucleus, organelles (organelles) and inclusions are located. Organelles are obligatory (or, at least, constantly found in certain categories of cells) components of the cytoplasm that perform a specific function and have a specific structure that is most appropriate for 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 inclusions of neutral fats and glycogen are the most widespread. The cytoplasm is stained with acidic dyes, and then two zones are clearly visible in it - the central one, which has a low viscosity and contains a significant number of inclusions (endoplasm), and the peripheral one with a 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 pancreatic glands, 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 the electron microscope. It turned out that the cytoplasm consists of the main substance (matrix, hyaloplasm), which contains two other important components - the endoplasmic reticulum and ribosomes, and in addition, organelles and inclusions. Hyaloplasm is a liquid or semi-liquid continuous phase between the denser components of the cytoplasm. The hyaloplasm is homogeneous or fine-grained, but sometimes fibrillar components (the so-called structural proteins) are found in it, creating some stability of this part of the cytoplasm and explaining its properties such as elasticity, contractility, stability (rigidity), etc. The viscosity of the cytoplasm, even of the same type of cells, is different: in sea urchin eggs it is 3 cps, and in paramecium 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 expanded cavities - cisterns. The endoplasmic reticulum, which forms the so-called vacuolar system of the cell, links the surface membrane of the cell, the cytoplasm, mitochondria and the nuclear envelope into one whole. Due to the existence of such a connection, a continuous metabolic exchange between all parts of the cell is possible.

Numerous ribosomes (granular type of endoplasmic reticulum) are located on the outer surface of the endoplasmic membranes of basophilic territories (ergastoplasm); the smooth type of this organoid is characteristic of the sites in which the synthesis of fats and carbohydrates occurs. The endoplasmic reticulum is found in all cells (with the exception of mature mammalian erythrocytes), but it is poorly developed in undifferentiated (eg, embryonic) cells and develops most strongly in actively metabolizing cells. Ribosomes are granules with a diameter of 150-350 Å. is 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 section 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 membrane 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 crucial for the active penetration of these substances into the cell or the protective capture of pathogenic microorganisms (bacteria, protozoa). In the cytoplasm, in some cases, the process of their neutralization occurs, while in others (for example, during a viral infection), on the contrary, their reproduction occurs.

The cytoplasm is the carrier of hereditary units that determine the properties of the organism that can be transmitted to offspring (cytoplasmic heredity). Korrens (S. Correns) first showed that variegation and defects in chlorophyll formation in plants depend on the presence and distribution of colorless and colored organelles - plastids, which are in charge of 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 later discovered in a variety of organisms. So, Ephrussi (V. Ephrussi) showed that, by acting with acridine compounds, it is possible to obtain a small hereditary yeast race. Its appearance is obviously associated with changes in mitochondria. In Drosophila, different sensitivity to the action of CO 2 is associated with cytoplasmic heredity transmitted through the egg. Finally, the antigenic properties of animal and human cells, transmitted from one generation to another, are also apparently determined 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 other components 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 cell life. So, in the process of division, the nuclear substance and the cytoplasm are mixed, and the mitotic apparatus is formed from the resulting myxoplasm (see Mitosis).

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