How the cell multiplies. Growth and reproduction of cells

Probably, there is not one more often studied in the school program on biology concepts than the cell. With her get acquainted in the 5th grade on natural history, then in 6 consider varieties and how the cell multiplies, its ways of division. In the 7th and 8th grades it is studied in terms of plant, animal and human belonging. 9 class implies the consideration of internal processes occurring in it, that is, the molecular structure. In 10 and 11, this is the cellular theory, discovery and evolution.

The program is built so because it is these small structures, the "bricks of life," that are the most important elements of any organism. All life functions, processes, growth and development, becoming - everything that is connected with life, is realized by them and in them. Therefore, in this article we will consider the main moments of reproduction, cell development and the history of their discovery.

Opening the cell

These structural particles are extremely small in size. Therefore, it took a lot of time and technology to open them. So, for the first time the cellular structure of living plant tissue was discovered by Robert Hooke. This was in 1665. In order to consider them, he invented the world's first microscope. This device resembled little modern magnifying devices. Rather, it was similar to several loops assembled between themselves, giving an increase.

Using this device, the scientist examined the slice of the cork tree. What he saw laid the foundation for the development of a number of related sciences and biology in general. A lot of tightly adjacent cells of approximately the same shape and size. Hooke called them cella, which means "cage".

Subsequently, a number of discoveries were made that allowed the knowledge to grow, accumulate and develop into several sciences engaged in their study.

1. 1675 - the scientist Malpighi studied the variety of cells in form and came to the conclusion that it is most often round or oval vials filled with vital juice.
2. 1682 - N. Grew confirmed Malpighi's conclusions, and also studied the structure of the cell membrane.
3. 1674 - Antonio van Leeuwenhoek opens the cells of bacteria, as well as blood structures and spermatozoa.
4. 1802-1809 - Sh. Brissot-Mirbe and J. B. Lamarck suggest the existence of tissues and the similarity of animals and plant cells.
5. 1825 - Purkinje opens the nucleus in the sex cell of birds.
6. 1831-1833 - Robert Brown reveals the presence of a nucleus in plant cells and introduces the notion of the importance of the internal composition, rather than the cell membrane, as was previously thought.
7. 1839 - Theodore Schwann concludes that all living organisms consist of cells, as well as the similarity of the latter among themselves (future cellular theory).
8. 1874-1875 years. - Chistyakov and Strasburger discover ways of multiplying cells - mitosis, meiosis.

All further discoveries in the field of the structure of cells, their functions, diversity and role in the life of organisms were accomplished quite quickly due to the intensive development of special magnifying and lighting equipment.

Reproduction of cells

Each cell during a lifetime performs a whole cellular cycle - this is the time of its life from the time of birth and to death (or division). Moreover, it does not matter whether it is animal or vegetable. The life cycle is the same for all of them, and most often, at the end of its cell multiply by division.

Of course, this process is not identical for all organisms. For eukaryotes and prokaryotes, it is fundamentally different, and there are some differences in the multiplication of plant and animal cells.

How does the cell multiply? There are several main ways for this.

1. Mitosis.
2. Meiosis.
3. Amitose.

Each of them represents a whole series of processes, phases. And all these processes are typical for multicellular organisms, both plant and animal origin. In single-celled reproduction occurs by simply dividing into two. That is, the methods of multiplication of cells are not the same. There is even such a phenomenon as cell suicide. It is self-destruction of cells instead of fission processes.

How does the cell multiply, for example, bacteria, blue-green algae, some protozoa? The sexless way, the simplest way: the contents of their cells are doubled, a transverse or longitudinal constriction is formed in the cell wall and one cell is divided into two completely new, identical to the mother's organism.

This process is called direct cell division. They multiply unicellular and bacteria, but it has nothing to do with either mitotic or meiotic processes. They occur only in the organism of multicellular living organisms.

Mitosis

Multicellular creatures contain billions of cells. And each of them seeks to complete its life cycle, namely, leaving offspring, not dying. Cells multiply by division, but this process is not the same for all of them.

Somatic structures (such include all cells of the body, except genital) by their method for reproduction choose mitosis or amitosis. This is a very interesting, capacious and complex process, as a result of which from one maternal diploid cell (that is, with a double set of chromosomes) two identical daughters with the same diploid structure are formed.

The whole process involves two main points:

1. Karyokinesis is the division of the nucleus and all its contents.
2. Cytokinesis - the division of protoplasm (cytoplasm and all cellular organelles).

These processes flow simultaneously, leading to the formation of full-scale maternal copies of a reduced size.

Mitosis consists of four phases (prophase, metaphase, anaphase, telophase) and a state preceding the division - interphase. Let's consider each detail.

Interphase

Growth and reproduction of cells is carried out throughout the life of the body. However, not all cells have the same life span. Some of them die after two or three days (uniform blood cells), some remain functioning for the rest of their lives (nervous).

But in the life of each cell most of the time this state is preserved, which is called the interphase. This is the period of preparation for the division of a mature, mature cell, which takes up to 90% of the time of the whole process.

Biological meaning of this stage in the accumulation of nutrients, RNA and proteins, the synthesis of DNA molecules. After all, after dividing into each daughter cell, exactly such an amount of organoids, substances and genetic material, as it was in the maternal body, should fall. For this, there must be a doubling of all available structures, including DNA strands.

In general, the interphase occurs in three stages:

• Presynthetic;
• synthetic;
• Post-synthetic.

The result: the accumulation of nutrients, energy and DNA molecules for further fission processes. Thus, this stage is just the beginning of how the cell multiplies in the future.

Prophase

At this stage, the following main processes occur:

• The nuclear envelope dissolves;
• Nucleoli disappear (dissolve);
• Chromosomes become visible in the microscope by twisting (spiraling) the structure;
• Centrioles diverge to the poles of the cell, stretching and forming a fission spindle.

At this stage, the reproduction of animal cells does not differ from that of all other cells.

Metaphase

This phase is rather short, only about 10 minutes. Its basis is that the chromatids are aligned along the equator of the cell. The filament spindle threads at one end cling to the centriole at the pole of the cell, and the other to the centromere of each chromatid. Between themselves, genetic structures are almost not connected and therefore are easily ready for disconnection.

Anaphase

The shortest stage of the whole mitotic cycle. The duration is about 3 minutes. During this period, each chromatid goes to its pole of the cell and completes the missing half, turning into a normal chromosome structure.

However, this enzyme requires a special enzyme called telomerase. It was his accumulation that was going on in the interphase.

The telophase

Each cell pole has its own genetic full material, which is clad in a nuclear envelope, forming a nucleus. Nucleoli appear. The whole process takes about 30 minutes. That is quite a long time. This is because the formation of nucleoli and nuclear envelope requires large energy costs, as well as the availability of building materials - nutrients (proteins, carbohydrates, enzymes, fats, amino acids).

Cytokinesis

This process completes the whole mitotic cycle. Protoplasm is divided together with organoids strictly in half, and each child receives exactly the same amount as her sister. Then a protein tightening (actin nature) is formed across the cell, which squeezes the structure across and divides it into two equal, but smaller cells than the maternal cell.

At this stage, there are some differences in the animal cell from how the plant cell multiplies . The fact is that there are fewer proteins in plant structures, and there is no actin at all. Therefore, in the middle is formed not peretyazhka, and the septum, on both sides of which cellulose is deposited. This gives the plant cell rigidity, forms a framework in the form of a cell wall.

The growth and multiplication of cells further follows the path of the usual life cycle: specialization, tissue formation, then organs, active work and division, or death.

Sex cells and their reproduction

On the question of how the cell multiplies, the answer can be given when specifying which one. After all, the mitosis processes we examined are characteristic only of somatic structures. Whereas the reproductive cells reproduce somewhat differently, or more precisely, meiosis.

This process is the basis of such vital functions in animals as gametogenesis, that is, sexual reproduction. The development of the sex cells occurs in many stages. Therefore, meiosis is an even more complex and capacious division than mitosis.

For plant cells, meiosis is the basis of sporogenesis, that is, the formation of sex cells. The basic biological role of meiosis for all organisms is that as a result of it, four haploid (with a half or a single set of chromosomes) sexual cells are formed. What for? In order for fertilization (the fusion of male and female sex cells) to occur, diploid recovery in a new zygote (future fetus) occurs. This gives genetic diversity to organisms, leads to a combination of genes, the appearance and consolidation of new traits.

Structure of the meiosis process

There are two main divisions in meiosis: reduction and equational. Each of them includes all the same phases as mitosis: prophase, metaphase, anaphase and telophase. Let's take a closer look at each of them.

Reduction division

Essence: from one diploid cell two haploid, with a half-set of chromosomes are formed. Phases:

• Prophase I;
• Metaphase I;
• Anaphase I;
• Telophase I.

At each phase, all the same transformations are repeated, as in the corresponding stages in mitosis. However, there is one difference: interphase does not double DNA, it only divides in half, and that's it. Therefore, only half of the genetic information falls into each daughter cell. This is the initial reproduction of animal cells, as well as plant, related to sex.

Equation division

The second division of meiosis, as a result of which two more cells are formed from each previous one. Now there are already four identical haploid analogues, which become the germ cells of animals or plants. Stages of equational division: prophase II, metaphase II, anaphase II, telophase II.

Thus, the question of how the cell multiplies has a rather complex and capacious answer. After all, these processes, like all others occurring in living beings, are very subtle and consist of many stages.