The mitosis phase is brief and clear, the most important. Mitosis. Stages of mitosis, their duration and characteristics. Amitosis

Among all the interesting and quite complex topics in biology, it is worth highlighting two processes of cell division in the body - meiosis and mitosis. At first it may seem that these processes are the same, since in both cases cell division occurs, but in fact there is a big difference between them. First of all, you need to understand mitosis. What is this process, what is interphase of mitosis and what role do they play in the human body? This will be discussed in more detail in this article.

A complex biological process that is accompanied by cell division and the distribution of chromosomes between these cells - all this can be said about mitosis. Thanks to it, chromosomes containing DNA are evenly distributed between the daughter cells of the body.

There are 4 main phases in the process of mitosis. They are all interconnected, since the phases smoothly transition from one to another. The prevalence of mitosis in nature is due to the fact that it is it that is involved in the process of division of all cells, including muscle, nerve, and so on.

Briefly about interphase

Before entering the state of mitosis, a cell that divides goes into interphase, that is, it grows. The duration of interphase can occupy more than 90% of the total time of cell activity in normal mode.

Interphase is divided into 3 main periods:

• phase G1;
• S-phase;
• phase G2.

They all take place in a certain sequence. Let's look at each of these phases separately.

Interphase - main components (formula)

Phase G1

This period is characterized by the preparation of the cell for division. It increases in volume for the further phase of DNA synthesis.

S-phase

This is the next stage in the interphase process, during which the body's cells divide. As a rule, the synthesis of most cells occurs over a short period of time. After division, the cells do not increase in size, but the last phase begins.

Phase G2

The final stage of interphase, during which cells continue to synthesize proteins while increasing in size. During this period, there are still nucleoli in the cell. Also, in the last part of the interphase, duplication of chromosomes occurs, and the surface of the nucleus at this time is covered with a special shell that has a protective function.

On a note! At the end of the third phase, mitosis occurs. It also includes several stages, after which cell division occurs (this process in medicine is called cytokinesis).

Stages of mitosis

As noted earlier, mitosis is divided into 4 stages, but sometimes there can be more. Below are the main ones.

Table. Description of the main phases of mitosis.

Important! The duration of the complete mitosis process, as a rule, is no more than 1.5-2 hours. The duration may vary depending on the type of cell being divided. Also, the duration of the process is influenced by external factors, such as light conditions, temperature, and so on.

What biological role does mitosis play?

Now let's try to understand the features of mitosis and its importance in the biological cycle. First of all, it ensures many vital processes of the body, including embryonic development.

Mitosis is also responsible for the restoration of tissues and internal organs of the body after various types of damage, resulting in regeneration. In the process of functioning, cells gradually die, but with the help of mitosis, the structural integrity of tissues is constantly maintained.

Mitosis ensures the preservation of a certain number of chromosomes (it corresponds to the number of chromosomes in the mother cell).

Video - Features and types of mitosis

Among all the interesting and quite complex topics in biology, it is worth highlighting two processes of cell division in the body - meiosis and mitosis. At first it may seem that these processes are the same, since in both cases cell division occurs, but in fact there is a big difference between them. First of all, you need to understand mitosis. What is this process, what is interphase of mitosis and what role do they play in the human body? This will be discussed in more detail in this article.

A complex biological process that is accompanied by cell division and the distribution of chromosomes between these cells - all this can be said about mitosis. Thanks to it, chromosomes containing DNA are evenly distributed between the daughter cells of the body.

There are 4 main phases in the process of mitosis. They are all interconnected, since the phases smoothly transition from one to another. The prevalence of mitosis in nature is due to the fact that it is it that is involved in the process of division of all cells, including muscle, nerve, and so on.

Briefly about interphase

Before entering the state of mitosis, a cell that divides goes into interphase, that is, it grows. The duration of interphase can occupy more than 90% of the total time of cell activity in normal mode.

Interphase is divided into 3 main periods:

• phase G1;
• S-phase;
• phase G2.

They all take place in a certain sequence. Let's look at each of these phases separately.

Interphase - main components (formula)

Phase G1

This period is characterized by the preparation of the cell for division. It increases in volume for the further phase of DNA synthesis.

S-phase

This is the next stage in the interphase process, during which the body's cells divide. As a rule, the synthesis of most cells occurs over a short period of time. After division, the cells do not increase in size, but the last phase begins.

Phase G2

The final stage of interphase, during which cells continue to synthesize proteins while increasing in size. During this period, there are still nucleoli in the cell. Also, in the last part of the interphase, duplication of chromosomes occurs, and the surface of the nucleus at this time is covered with a special shell that has a protective function.

On a note! At the end of the third phase, mitosis occurs. It also includes several stages, after which cell division occurs (this process in medicine is called cytokinesis).

Stages of mitosis

As noted earlier, mitosis is divided into 4 stages, but sometimes there can be more. Below are the main ones.

Table. Description of the main phases of mitosis.

Important! The duration of the complete mitosis process, as a rule, is no more than 1.5-2 hours. The duration may vary depending on the type of cell being divided. Also, the duration of the process is influenced by external factors, such as light conditions, temperature, and so on.

What biological role does mitosis play?

Now let's try to understand the features of mitosis and its importance in the biological cycle. First of all, it ensures many vital processes of the body, including embryonic development.

Mitosis is also responsible for the restoration of tissues and internal organs of the body after various types of damage, resulting in regeneration. In the process of functioning, cells gradually die, but with the help of mitosis, the structural integrity of tissues is constantly maintained.

Mitosis ensures the preservation of a certain number of chromosomes (it corresponds to the number of chromosomes in the mother cell).

Video - Features and types of mitosis

Prophase. During prophase, chromosomes condense and become visible under light microscopy. As DNP compacts, chromosomes acquire the structure of well-stained threads. The number of chromosomes is 4n, which corresponds to the amount of DNA 4c. Due to the inactivation of genes in the region of the nucleolar organizer and the inhibition of RNA synthesis in prophase, the disappearance of nucleoli is noted. The nuclear envelope gradually disintegrates into fragments and small membrane vesicles. At the same time, centrioles diverge to opposite poles of the cell.
In satellite site of the mother centriole the formation of microtubules begins, from which the filaments of the spindle are formed.

Metaphase. A characteristic event of metaphase is the movement of chromosomes to the equatorial plane of the spindle. Here they are located strictly regularly, forming a metaphase plate (when looking at the spindle from the side). If we consider a group of metaphase chromosomes from the side of the spindle poles, a figure resembling a star (the so-called mother star) clearly appears. During this period, it is possible to determine the number, shape and size of the chromosomes (d-chromosomes, double chromosomes) that make up the metaphase plate.
By the end of metaphase the longitudinal halves of the chromosomes (sister chromatids) are separated throughout, except for the zone of primary constriction.

For each type animals characterized by a strictly constant number of chromosomes in somatic cells. For humans, it is 46. The length of the chromosomes distinguishes between the alternation of colored and uncolored areas. Moreover, each chromosome has a unique pattern of differential coloring. Human chromosomes are divided into 7 groups according to their size and structural features (A, B, C, D, E, F, G) and each chromosome has its own number. The set of characteristics of the structure of chromosomes, their size and number constitutes what is called a karyotype.

Anaphase involves the process of divergence of chromosomes to the poles of a dividing cell. The mechanism of chromosome movement is explained by the sliding filament hypothesis, according to which spindle filaments consisting of microtubules, interacting with each other and with contractile proteins, pull chromosomes towards the poles. The speed of chromosome movement reaches 0.2-0.5 µm/min, and the entire anaphase lasts 2-3 minutes. Anaphase ends with the movement of two identical sets of chromosomes (s-chromosomes, or single chromosomes) to the poles, where they come together, forming figures that resemble stars in appearance (when viewed from the pole). These figures are called daughter stars.

Because chromosome stars are formed at each pole, this stage of mitosis is sometimes called the double star stage (diaster), or the stage of daughter stars. Telophase- the final stage of mitosis, during which daughter nuclei are reconstructed at the spindle poles. The rearrangement of telophase chromosomes resembles the processes of their change in prophase, but occurring in the opposite direction. When chromosomes interact with membrane vesicles of the cytoplasm, the nuclear envelope is formed. With the transition of chromosomes to the interphase state, new nucleoli are formed. Telophase ends with the division of the cell body - cytotomy, or cytokinesis, which leads to the formation of two daughter cells.

Part of the cells can exit the reproductive cycle and enter the path of differentiation. Some cells may exit the cell cycle in the G1 period or after the S period and remain at rest (Go period). Such resting cells retain the ability to divide and can again enter the reproduction cycle.

Educational video: cell mitosis and its stages

The growth and development of living organisms is impossible without the processes of cell division. One of them is mitosis - the process of division of eukaryotic cells in which genetic information is transmitted and stored. In this article you will learn more about the features of the mitotic cycle and get acquainted with the characteristics of all phases of mitosis, which will be included in the table.

The concept of "mitotic cycle"

All processes that occur in a cell, starting from one division to another, and ending with the production of two daughter cells, are called the mitotic cycle. The life cycle of a cell is also a state of rest and a period of performing its direct functions.

The main stages of mitosis include:

• Self-duplication or reduplication of the genetic code, which is transmitted from a mother cell to two daughter cells. The process affects the structure and formation of chromosomes.
• Cell cycle- consists of four periods: presynthetic, synthetic, postsynthetic and, in fact, mitosis.

The first three periods (presynthetic, synthetic and postsynthetic) refer to the interphase of mitosis.

Some scientists call the synthetic and postsynthetic period the preprophase of mitosis. Since all stages occur continuously, smoothly moving from one to another, there is no clear division between them.

The process of direct cell division, mitosis, occurs in four phases, corresponding to the following sequence:

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

Rice. 1. Phases of mitosis

You can find a brief description of each phase in the “Phases of Mitosis” table, which is presented below.

Table "Phases of Mitosis"

The process of cytotomy in an animal cell occurs using the cleavage furrow, and in a plant cell - using the cell plate.

Atypical forms of mitosis

Atypical forms of mitosis are sometimes found in nature:

• Amitosis - a method of direct division of the nucleus, in which the structure of the nucleus is preserved, the nucleolus does not disintegrate, and chromosomes are not visible. The result is a two-nucleate cell.

Rice. 2. Amitosis

• Polythenia - DNA cells increase multiple times, but without increasing the chromosome content.
• Endomitosis - During the process after DNA replication, there is no separation of chromosomes into daughter chromatids. In this case, the number of chromosomes increases tens of times, polyploid cells appear, which can lead to mutation.

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With identical genetic material.

Interphase

Before a dividing cell enters mitosis, it undergoes a period of growth called interphase. About 90% of a cell's time can normally be spent in interphase, which occurs in three main phases:

• Phase G1: period before DNA synthesis. In this phase, the cell increases in mass, preparing to divide.
• S-phase: the period during which DNA synthesis occurs. In most cells this stage occurs in a very short period of time.
• Phase G2: the cell continues to synthesize additional proteins and increases in size.

During the last part of interphase, the cell still has nucleoli. The nucleus is bounded by the nuclear envelope and is duplicated, but in the form of chromatin. The two pairs of centrioles, formed from the replication of one pair, are located outside the nucleus.

After the G2 phase, mitosis occurs, which in turn consists of several stages and ends with cytokinesis (cell division).

Mitosis phases:

Preprophase (in plant cells)

Preprophase is an additional phase during mitosis that is not found in other eukaryotes such as animals or fungi. It precedes prophase and is characterized by two different events.

Changes that occur in preprophase:

• Formation of a preprophase band - a dense microtubular ring under.
• Beginning of microtubule nucleation in the nuclear envelope.

Prophase

In prophase it condenses into discrete chromosomes. The nuclear envelope breaks down and spindles form at opposite poles of the cell. Prophase (compared to interphase) is the first true step of the mitotic process.

Changes that occur in prophase:

• Chromatin fibers turn into chromosomes, each having two, connected to form a centromere. Fission fibers, consisting of microtubules and proteins, are formed in.
• In animal cells, fission fibers initially appear as structures called asteres that surround each pair of centrioles.
• Two pairs of centrioles (formed from the replication of one pair in interphase) move away from each other to opposite poles of the cell due to the elongation of microtubules formed between them.

Prometaphase

Prometaphase is the phase of mitosis after prophase and preceding metaphase in eukaryotic somatic cells. Some sources attribute the processes occurring in prometaphase to late prophase and the initial stage of metaphase.

Changes that occur in prometaphase:

• The nuclear envelope disintegrates.
• Polar fibers, which are microtubules that make up the spindle fibers, move from each pole to the equator of the cell.
• Kinetochores, which are specialized regions at the centromeres of chromosomes, are attached to a type of microtubule called kinetochore filament.
• The kinetochore filaments “interact” with the spindle.
• Chromosomes begin to migrate to the center of the cell.

Metaphase

In metaphase, the fission fibers are fully developed and the chromosomes are aligned on the metaphase (equatorial) plate (a plane that is equally distant from the two poles).

Changes that occur in metaphase:

• The nuclear membrane completely disappears.
• In animal cells, the two pairs move in opposite directions towards the poles of the cell.
• Polar fibers (microtubules that make up the spindle fibers) continue to spread from the poles to the center. The chromosomes move randomly until they attach (via their kinetochores) to the polar fibers on either side of the centromeres.
• The chromosomes are aligned on the metaphase plate at right angles to the spindle poles.
• The chromosomes are held on the metaphase plate by equal forces of polar fibers, which press on their centromeres.

Anaphase

In anaphase, paired chromosomes () separate and begin to move to opposite ends (poles) of the cell. Spindle fibers not connected to chromatids elongate and lengthen the cell. At the end of anaphase, each pole contains a complete compilation of chromosomes.

Changes that occur during anaphase:

• The paired ones in each individual chromosome begin to move apart.
• Once paired sister chromatids are separated from each other, each is considered a "complete" chromosome. These are called daughter chromosomes.
• With the help of the division spindle, they move to the poles at opposite ends of the cell.
• The daughter chromosomes first migrate to the centromere, and the kinetochore strands become shorter than the chromosomes near the poles.
• In preparation for telophase, the two poles of the cell also move away from each other during anaphase. At the end of anaphase, each pole contains a complete compilation of chromosomes.
• The process of cytokinesis (separation of the cytoplasm of the original cell) begins, which ends after telophase.

Telophase

During telophase, chromosomes reach the nuclei of new daughter cells.

Changes that occur during telophase:

• The polar fibers continue to elongate.
• Nuclei begin to form at opposite poles.
• The nuclear membranes of new nuclei are formed from remnants of the nuclear membrane of the mother cell and pieces of the endomembrane system.
• Nucleoli appear.
• Chromatin fibers of chromosomes unwind.
• After these changes, telophase and mitosis are largely completed, and the genetic content of one cell is divided into two parts.

Cytokinesis

Cytokinesis is the division of the cytoplasm of a cell. It begins before the end of mitosis in anaphase and ends shortly after telophase. At the end of cytokinesis, two genetically identical daughter cells are formed.

Daughter cells

At the end of mitosis and cytokinesis, the chromosomes are distributed equally between the two daughter cells. These cells are identical, each containing a complete set of chromosomes.

Cells produced through mitosis are different from cells produced through . Meiosis produces four daughter cells. These cells are cells containing half the number of chromosomes of the original cell. undergo meiosis. When germ cells divide during fertilization, haploid cells become diploid cells.

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