What is the cytoplasm? Structure, composition and properties of the cytoplasm

What is the 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 a colloidal solution, the structure of cell membranes and the most important cellular organelles.

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

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

• Prokaryotic;
• Eukaryotic.

They have many differences in their structure. In the prokaryotic cell, the structurally formed nucleus is absent. Its single chromosome is located directly in the cytoplasm, that is, it does not separate from other elements. This structure is characteristic of bacteria. Their cytoplasm is poor in structure of structures, but in it there are small ribosomes. Eukaryotic is much more complicated than a prokaryotic cell. Its DNA, associated with a protein, is located in chromosomes, located in a separate cellular 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 with the two types of cellular organization. Both prokaryotes and eukaryotes have a membrane. And their internal contents are represented by a special colloidal solution, in which there are various organoids and temporary inclusions.

Eukaryotic cell: cytoplasm. Its composition and functions

So, we pass to the essence of our research. What is the cytoplasm? Let's take a closer look at this cellular education. The cytoplasm is the 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, the cytoplasm can be understood as a colloidal solution, which is characterized by the movement of colloidal particles and other components. In this semiliquid medium consisting of water, various organic and inorganic compounds, there are cellular structures-organoids, as well as temporal inclusions. The most important functions of the cytoplasm are as follows. It performs the design of all cellular components in a single system. Due to the presence of tubules and microtubules, the cytoplasm acts as a cellular skeleton and provides the environment for physiological and biochemical processes. In addition, it provides an opportunity for the functioning of all cellular organelles and provides movement. These functions of the cytoplasmic cell are extremely important, since they allow the structural unit of all living things to carry out their normal vital activity. Now you know what cytoplasm is. And also aware of what position in the cell it takes and what "work" it performs. Next, we will consider the composition and structure of the colloidal solution in more detail.

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

Membrane organoids in a colloidal solution are the Golgi apparatus, endoplasmic reticulum, mitochondria, lysosomes, plastids and external cytoplasmic membrane. In the cells of animals and plants, the composition of the semiliquid medium differs. The cytoplasm in the plant cell has special organoids - plastids. They are specific protein bodies that differ in function, shape and color pigments in different colors. Plastids are located in the cytoplasm and are able to move along with it. They grow, multiply and produce organic compounds containing enzymes. The cytoplasm in the plant cell has three kinds of plastids. Yellowish or orange are called chromoplasts, green ones are called chloroplasts, and colorless ones are called leukoplasts. There is one more characteristic feature - the Golgi complex is represented by dictyosomes scattered throughout the cytoplasm. In animal cells, in contrast to plant cells, there are 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 layer is located between it and the porous nuclear membrane. The ectoplasm has in its composition a large number of microfilaments - filaments from globular protein actin molecules. Endoplasma 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 mucous, colorless, heterogeneous solution in which the metabolic processes are constantly occurring. Hyaloplasma (in other words, matrix) is a colloidal system with a complex structure. Its composition includes soluble RNA and proteins, lipids and polysaccharides. Even in the hyaloplasm contains a significant number of nucleotides, amino acids, as well as ions of inorganic compounds such as Na ^- or Ca ²⁺ . The matrix has no homogeneous structure. It is presented in two forms, which are called gel (solid) and sol (liquid). Between them there are mutual transitions. In the liquid phase, there is a system of the thinnest protein filaments, which are called microtubulets. They bind all the structures inside the cell. And in the places of their intersection there are groups of ribosomes. Microtradericles together with microtubules and microfilaments form a cytoplasmic skeleton. It determines and organizes the location of all cellular organelles.

Organic and inorganic substances in a colloidal solution of a cell

Let's consider, what is the chemical composition of the cytoplasm? The 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 molecules of polysaccharides consist of monosaccharides. In the cell they are represented by starch, glycogen and cellulose. Lipids, that is, fat molecules, are formed by residues of glycerin and fatty acids. Structure of the cytoplasm: Inorganic substances are primarily water, which, as a rule, amounts to 90% of the mass. It performs important functions in the cytoplasm. Water is a universal solvent, gives elasticity, takes a direct part in the movement of substances both inside and between cells. As for macroelements forming the basis of biopolymers, more than 98% of the total cytoplasm composition occupy oxygen, hydrogen, carbon and nitrogen. Besides 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 medium.

Properties of a colloidal solution in a cell

Let us further consider what are the main properties of the cytoplasm. First, it is a constant cyclosis. It is the intracellular movement of the cytoplasm. It was first recorded and described in the 18th century by the Italian scientist Corti. Cyclosis is carried out in the entire protoplasm, including in the strands that bind the cytoplasm to the nucleus. If the movement ceases for some reason, the eukaryotic cell dies. The cytoplasm is necessarily in a constant cyclosis, which is detected by the movement of organelles. The rate of motion of the matrix depends on various factors, including light and temperature. For example, in the epidermis of onion scales, the rate of cyclosis is about 6 m / s. The movement of the cytoplasm in the plant organism has a huge impact on its growth and development, facilitating the transport of substances between the cells. The second important property is the viscosity of the colloidal solution. It varies greatly depending on the type of organism. In some living creatures, the viscosity of the cytoplasm can be quite insignificantly higher than the viscosity of water, in others, on the contrary, it can reach the viscosity of glycerin. It is believed that it depends on the metabolism. The more intensive 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, thanks to their special structure, have the ability to selectively pass molecules of certain substances and not let others pass. The selective permeability of the cytoplasm plays an important role in the process of vital activity. 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 participates in energy metabolism, transport of nutrients, excretion of exotoxins. Also, the matrix is considered an osmotic barrier and participates in the regulation of development, growth and cell division. Including cytoplasm plays an important role in the replication of DNA.

Features of cell reproduction

All plant and animal cells multiply by division. Three types are known: indirect, direct and reduction. The first one is called amitosis. Indirect multiplication occurs as follows. Initially, the nucleus is "ligated," and then the cytoplasm divides. As a result, two cells are formed, which gradually grow to the size of the maternal. This kind of division in animals is extremely rare. As a rule, they have an indirect division, i.e. 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 doubling the amount of DNA. Mitosis has four phases, called prophase, metaphase, anaphase and telophase.

• The first phase is characterized by the formation of a tangle of chromatin filaments at the site of the nucleus, and subsequently chromosomes in the form of "hairpins". During this period, the centrioles diverged toward the poles and the formation of an achromatic spindle of division.
• The second stage of mitosis is characterized by the fact that chromosomes, reaching maximum spiralization, begin to settle on the equator of the cell in an orderly manner.
• In the third phase, the chromosome is split into two chromatids. In this case, the spindle threads contract and pull the daughter chromosomes to opposite poles.
• In the fourth phase of mitosis, chromolysis disparilization occurs, as well as the formation of a nuclear envelope around them. At the same time, the cytoplasm is divided. The daughter cells have a diploid set of chromosomes.

Reduction division is peculiar only to sex cells. With this type of cell reproduction, formation of chromosomes from paired formations takes place. An exception is one unpaired chromosome. As a result of reduction division in two daughter cells, a half chromosome set is obtained. Unpaired is in only one daughter cell. Sex cells that have a half set of chromosomes, ripe and capable of fertilization, are called female and male gametes.

The concept of the cytoplasmic membrane

All cells of animals, 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 covers the cytoplasm. It includes three subsystems:

• A plasma membrane;
• Supramembrane complex;
• Submembrane support and contraction apparatus of the hyaloplasm.

The structure of the membrane of the cytoplasm is as follows: it contains two layers of lipid molecules (bilayer), each such molecule having a tail and a head. The tails are facing each other. They are hydrophobic. The heads are hydrophilic and inward and outwardly facing the cells. The protein molecules are included in the bilayer. And it is asymmetric, and in the monolayers are located different lipids. 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, with their carbohydrate chains always directed outwards. 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. Plasmalemma carries the transfer of substances inside the cell, as well as their release to the outside, that is, isolation. Through the pores penetrate water, ions and small molecules of substances, and large solid particles are transported to the cell with the help of phagocytosis. On the surface of the membrane forms microvilli, invagination and protrusion, 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" to different surfaces and facilitates movement.

Organoids in the cytoplasm. Endoplasmic reticulum and ribosomes

In addition to hyaloplasm, the cytoplasm also contains many microscopic organoids, which 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 body or animals, which made it possible to call them organoids. In the cytoplasm, the organelles visible in the light microscope are distinguished: a platelet complex, mitochondria, and a centrosome. Using an electron microscope, microtubules, lysosomes, ribosomes and a plasma network are detected in the matrix. The cytoplasm of the cell is penetrated by various channels, which have been termed 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, which look like tiny granules. They can be located singly or in groups. Ribosomes consist of almost equal amounts of ribonucleic acid and proteins. Also included in their composition is magnesium. Ribosomes can not only be in the channels of EPS, but also freely lie in the cytoplasm, and also occur in the nucleus, where they are formed. The aggregate of channels having ribosomes is called a granular endoplasmic reticulum. On them, except ribosomes, are enzymes that promote the synthesis of carbohydrates and fats. In the internal cavities of the channels are the products of the vital activity of the cell. Sometimes in the expansion of EPS, vacuoles are formed-cavities filled with cell juice and bounded by a membrane. These organelles support the turgor pressure. Lysosomes are small formations of the oval form. They are scattered through the cytoplasm. Lysosomes are formed in EPS or Golgi complex, where they are filled with hydrolytic enzymes. Lysosomes are designed to digest particles trapped inside the cell due to phagocytosis.

Cytoplasm: structure and function of its organoids. The Golgi plate complex, mitochondria and centrosome

The Golgi complex is represented in plant cells by separate bodies, decorated with membranes, and in animals by tubules, bubbles and cisterns. This organoid is intended for chemical alteration, compaction and subsequent release into the cytoplasm of products of cellular secretion. It also synthesizes polysaccharides and the formation of glycoproteins. Mitochondria - this body is rod-shaped, filiform or granular. They are limited to two membranes, which consist of double layers of phospholipids and proteins. From the internal membranes of these organelles the cristae, on whose walls the enzymes are located, depart. With their help, adenosine triphosphate (ATP) is synthesized. Mitochondria are sometimes called "cellular power plants", since they supply a significant portion 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. 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 protozoa and lower fungi) and is responsible for determining the poles in mitosis. In the dividing cell, the centrosome is first divided. In this case, an achromatin spindle is formed, which sets the reference points for chromosomes diverging to the poles. In addition to the indicated organoids, special organelles can be found in the cell, for example, cilia and flagella. Also, at certain stages of life, there may be inclusions in it, that is, temporary elements. For example, such nutrients as: droplets of fat, proteins, starch, glycogen, etc.

Lymphocytes are the most important cells of the immune system

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

• Small - less than 8 μm in diameter;
• Average - with a diameter of 8 to 11 microns;
• Large - a diameter of more than 11 microns.

Small lymphocytes predominate in the blood of animals. They have a large rounded nucleus, which predominates over the cytoplasmic volume. The cytoplasm of the lymphocytes of this subgroup looks like a nuclear rim or a sickle adjacent to any side of the nucleus. Often, the matrix contains a small amount of azurophilic granules. Mitochondria, the elements of the plate complex and the tubules of EPS 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. In them it is easy to distinguish the nucleolus. The cytoplasm of the lymphocytes of the second and third groups has a wider rim. Two classes of lymphocytes are known, the so-called B- and T-lymphocytes. The first are formed in animals in the myeloid bone marrow tissue. 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 are surface histocompatibility antigens, as well as numerous receptors, through which the recognition of foreign particles. Small lymphocytes are mainly represented by T-lymphocytes (more than 70%), among which there is a large number of long-living cells. The vast majority of B-lymphocytes live not for long - from one week to a month.

We hope our article has proved useful, and now you know what cytoplasm, hyaloplasm and plasmolemma are. And also aware of what the functions, structure and significance for the life of the organism of these cellular formations.