In nature, there is a method for dividing eukaryot cells, in which the doubling process first occurs, and then the uniform distribution of genetic material between the resulting daughter cells. Such a division in biology is called mitosis. In this article, you know more about the main stages of this division process, you can consider it in the schemes.

Phase mitosis

The process of dividing eukaryotes occurs in four stages:

• Prophase;
• Metaphase;
• Anaphase;
• Bulfase.

Some scientists at the initial stage consider more phases. For example, the proofased precedes prefaffase (the so-called preparation for division), and in front of metaphase is isolated by Promethaz. However, in most educational publications, all these additions are combined into a single refueling of mitosis.

Fig. 1. Stages of mitosis

The entire division process occurs continuously, therefore each mitosis phase is smoothly replaced by a subsequent phase.

Let's look at each of them separately:

• Prophase ;

At this stage, centrioles that play a large role during the division of the animal cell are clearly visible.

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There are no centrioles in the vegetable cell core, therefore, the division of an animal cell is mainly shown in mitosis. And all because the presence of centrioles makes the division process more visual.

Fig. 2. Mitosis scheme

During the proofased, centrioles are divided and diverge in poles. Microtubules are deployed from them, which are threads of the separation of division. It is it that regulates the discrepancy of chromosomes to different poles of the cell, which is divided. The yelt threads have a different appointment: some are attached to the center meters of chromosomes, others are stretched from the pole to the pole.

At the end of the opposite, the nuclear shell dissolves, and the nucleolo, chromosome spirals, as a result of which they become shorter and thicker. At this stage, they can be clearly seen in the light microscope.

• Metafaza ;

At this stage, the spiral chromosomes are visible more clearly, as they move to the equator of the separation of division. Chromatids are also well viewed, each of the chromosomes are two. In the course of metafase mitosis in the microscope, you can see that chromatids have a lamp - centruller. It is with its help chromosome attached to spindle. As soon as the centromer is divided, each chromatide becomes an independent subsidiary of chromosome.

• Anaphase ;

It is the shortest phase, during which each independent chromatide is dispersed to different poles.

• Bulphaz ;

Now the chromosome is again dragged and acquired the original appearance. There is a nuclear shell around them with a nuclear fuel inside. Ribosomes are formed in it. Spindle divisions disappear, chromosomes are no longer visible in the light microscope. There is a uniform distribution of the cytoplasm and its organoids between two subsidiaries.

The result of mitosis

The entire division of division on average takes up to two hours. However, it directly depends on external factors: temperature, light and other indicators.

As a result, we obtain from one cell at once two, which have the same genetic information. Thus, a constant number of DNA remains.

Thanks to mitosis provided:

• the growth of the body;
• transmission of hereditary information;
• there is a process of sexual reproduction in some representatives of wildlife;

An example of non-reproduction is the vegetative reproduction of plants, taking the hydra and so on.

Fig. 3. Methods of vegetative reproduction of plants

• restoration of tissue cells.

What did we know?

The process of cell division in which genetic information is preserved is called mitosis. It occurs in four phases: proofased, metaphase, anatherapy, belly. Each of them has its own characteristics and meaning. As a result of dividing from one maternal cell, two subsidiaries with the same chromosomal set is formed. Thanks to the mitosis, the body's growth and development of the body, the restoration of tissue cells, the most powerful reproduction, and most importantly - transmission from generation to generation of genetic code is possible.

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Mitosis - This is the most common way to divide eukaryotic cells. In the mitosis of the genome of each of the two cells formed, identical to each other and coincide with the genome of the source cell.

Mitz is the last and usually the shortest stage of the cell cycle. With its end, the life cycle of the cell ends and the cycles of two newly educated.

The diagram illustrates the duration of the phases of the cell cycle. The letter M is marked by mitosis. The greatest rate of mitosis is observed in the embryonic cells, the smallest - in the tissues with high degree Differentiation if their cells are generally divided.

Although mitosis is considered regardless of the interphase consisting of G 1, S and G 2 periods, the preparation for it occurs in it. Most. an important point is a DNA replication occurring in a synthetic (s) period. After replication, each chromosome consists of two identical chromatids. They are brought together throughout their length and are combined in the field of chromosome centromosome.

In the chromosome interfase are in the core and are a tangle of thin very long chromatin yarns, which are visible only under the electron microscope.

In mitosis, a number of consecutive phases are distinguished, which can also be called stages or periods. With a classic simplified version of the consideration, four phases are isolated. it proofase, metaphase, anal and bodaffase. Often allocate more phases: promethaz (between proofas and metaphase), prep Proceed (Characteristic for plant cells precedes proofas).

With mitosis, another process is connected - cytokinezwhich proceeds mainly during the period of telfase. It can be said that cytokinesis is, as it were, an integral part of the belly, or both of the process are in parallel. Under cytokine, the separation of the cytoplasm (but not nucleus!) Parental cells. The core division is called kariorosisAnd it precedes cytokinesu. However, during mitosis, as such, the nucleus does not occur, since one - the parent disintegrates first, then two new subsidiaries are formed.

There are cases when kariokinesis occurs, and cytokines - no. In such cases, multi-core cells are formed.

The duration of mitosis itself and its phases is individual, depends on the type of cells. Usually, proofas and metaphase is the longest periods.

The average duration of mitosis is about two hours. Animal cells are usually divided faster than plant cells.

In the division of eukaryot cells, two-pole spine divisions consisting of microtubules and associated proteins are formed. Due to it, there is an equal distribution of hereditary material between the daughter cells.

Below will be a description of the processes that occur in the cell in various mitosis phases. The transition to each top phase is controlled by special biochemical control points in which "is checked", whether all the necessary processes were properly completed. In the case of errors, division may stop, and maybe - not. In the latter case, abnormal cells occur.

Phase mitosis

Prophase

The following processes occur in the Proofase (mainly parallel):

Chromosomes are condensed

Nucleoli disappear

Nuclear shell decay

Two poles are formed

Mitz begins with shortening chromosomes. The components of their pairs of chromatide spiral are, as a result of which the chromosomes are shortened and thicken. By the end of the opposite, they can be seen in the light microscope.

The nuclei disappear, since the chromosomes (nucleotone organizers) form them are already in spiralized form, therefore, inactive and do not interact with each other. In addition, nucleoline proteins are disintegrated.

In the cells of animals and lower plants, the centrioles of the cellular center differ in the poles of the cell and perform centers of the organization of microtubule. Although the highest plants there are no centrioles, microtubules are also formed.

From each center of the organization, short (astral) microtubules begin to disperse. The structure is formed similar to the star. In plants, it does not form. Their fission poles are wider, microtubules are not small, but from a relatively wide area.

The decay of the nuclear shell on fine vacuoles marks the end of the opposite.

On the right on micrographs with green, microtubule, blue - chromosomes, red - chromosome centrometers are highlighted.

It should also be noted that during the protozoase of mitosis, the EPS fragmentation occurs, it disintegrates into small vacuoles; The Golgi apparatus disintegrates into separate docyoma.

Promethaface.

Key processes of production processes go mostly sequentially:

Chaotic location and movement of chromosomes in the cytoplasm.

Connect them with microtubes.

Movement of chromosomes into the equatorial cell plane.

Chromosome turn out to be in the cytoplasm, they move randomly. Once on the poles, they have more chances to rest on the plus-end of microtubule. In the end, the thread is attached to the kirethor.

Such a digital microtubule begins to grow than remove chromosome from the pole. At some point, another microtubule is fastened to the Chromatide Kirethor, increasing from another division pole. She also begins to push chromosoma, but already in the opposite direction. As a result, the chromosome becomes equator.

The kinetokhors are protein formations on chromosome centromosomes. Each nursing chromatide has his own kinetchor, which "matures" in the opposition.

In addition to astral and kinetrochoric microtubules there are those that come from one pole to another, as if cutting a cell in a perpendicular equator to the direction.

Metafaza

The sign of the start of the metafase is the location of the chromosome by equator, the so-called is formed methazna, or Equatorial, plate. The amount of chromosomes are clearly visible to the metaphase, their differences and the fact that they consist of two nursing chromatids connected in the center of centromers.

Chromosomes are held at the expense of the balanced tension forces of microtubules of different poles.

Anaphase

Nursing chromatids are divided, each moves to its pole.

Poles are removed from each other.

Anphasis is the shortest phase of mitosis. It begins when the centeriers of chromosomes are divided into two parts. As a result, each chromatide becomes an independent chromosome and it turns out to be attached to the microtube of one pole. Thread "pull" chromatids to the opposite poles. In fact, microtubules are disassembled (depolymerizes), i.e., shortening.

In the anatherapy of animal cells, not only subsidiary chromosomes are moving, but also the poles themselves. At the expense of other microtubes, they are sweeping, astral microtubules are attached to the membranes and also "pull".

Bulphaz

The movement of chromosomes stops

Chromosome deconentials

Nuclei appear

Restores nuclear shell

Most of the microtubule disappears

Bulfase begins when chromosomes stop moving, stopping at the poles. They are dragged, become long and filamentous.

Microtubules spine separation are destroyed from poles to the equator, i.e., on the part of their minus, ends.

A nuclear shell is formed around the chromosoma by merging the membrane bubbles, which the parent kernel and EPS broke up in the opposition. At each pole, its subsidiary is formed.

Since chromosomes are dragged, the nucleotone organizers become active and nuclei appear.

RNA synthesis is resumed.

If on the poles of centrioles is not yet steaming, then each of each is drawn by a steam room. Thus, at each pole, its cellular center is recreated, which will go into a subsidiary.

Usually, the elephant ends with the separation of the cytoplasm, i.e. cytokinesis.

Cytokinez

Cytokines can begin in Anafase. By the beginning of cytokinesis, cellular organelles are distributed relatively evenly through the poles.

The separation of cytoplasm of plant and animal cells occurs differently.

In animal cells, due to the elasticity, the cytoplasmic membrane in the equatorial part of the cell is beginning to be filled into inside. A furridge is formed, which in the end closes. In other words, the maternal cell is divided by a habit.

In vegetable cells in the bodily filament, the spindle is not disappearing in the equator area. They are shifted closer to the cytoplasmic membrane, their number increases, and they form fragmoplast. It consists of short microtubes, microfilaments, parts of EPS. Ribosomes, mitochondria, Golgi complex move here. Golgi bubbles and their contents at the equator form a median cellular plate, cell walls and a daughter cell membrane.

Mitosis value and function

Thanks to mitosis, genetic stability is provided: accurate reproduction of genetic material in a number of generations. The cores of new cells contain as many chromosomes as their parent cell contained, and these chromosomes are accurate copies of the parents (unless mutations did not arise). In other words, daughter cells are genetically identical to the maternal.

However, mitosis also performs a number of other important functions:

the growth of a multicellular organism,

miscellaneous reproduction

replacement of cells of various tissues in multicellular organisms,

some species may receive regeneration of body parts.

Mitosis - This division of the cell, in which the daughter cells are genetically identical to the maternal and among themselves. That is, in mitosis, the chromosomes double and are distributed between the daughter cells so that each obtained each chromatide each chromosome.

Mitoses allocate several stages (phases). However, the Mitoz itself is preceded by a long interfhaza. Mitosis and interphase together make up a cell cycle. In the process of interphase, the cell is growing, organides are formed in it, synthesis processes actively go. In the synthetic period, the interphalazes is reduced, i.e. doubles, DNA.

After doubling chromatids, they remain connected in the area centrometers, i.e. chromosome consists of two chromatids.

In Mitoz itself, four main stages usually allocate (sometimes more).

The first stage of mitosis - prophase. In this phase chromosome spiral and acquire a compact twisted form. Because of this, the RNA synthesis processes become impossible. Nuclei disappear, and therefore ribosomes are also not formed, i.e., synthetic processes in the cell are suspended. Centrioles are diverted to the poles (in different ends) of the cells, the spindle divisions begins to form. At the end of the opposity, a nuclear shell decays.

Promethaface - This is a stage that is not always distinguished separately. The processes occurring in it may attribute to late proofas or early metaphase. In the chromosome industaphase, the cytoplasm is randomly moved along the cell while in the area of \u200b\u200bthe centromeres will not be connected to the thread of the spindle of the division.

The thread is a microtubule built of tubulin protein. She increases the attachment of new tubulin subunits. At the same time, the chromosome moves from the pole. From the other pole to it, the thread of the spindle is also joined and also pushes it from the pole.

Second stage of mitosis - metafaza. All chromosomes are located in the equatorial region of the cell nearby. Two threads are attached to their centromeres. In metaphase mitosis, the longest stage.

The third stage of mitosis - anaphase. In this phase, the chromatids of each chromosome is separated from each other and due to the filaments pulling their threads, the division is departed to different poles. Microtubule now do not grow, but disassemble. Anphase fairly fast phase mitosis. With a discrepancy with chromosomes, the cells of the cell approximately in equal amounts also diverge to the poles.

The fourth stage of mitosis - bulphaz - largely inverse proofas. Chromatids are collected in the cell poles and are spinning, i.e., despiryalize. Around them are formed nuclear shells. Rangers are formed, the synthesis of RNA begins. Relieved divisions begins to collapse. Next is the division of the cytoplasm - cytokinez. In animal cells, this occurs due to the phenomenon of the membrane inside and the formation of drying. In the cells of plants, the membrane begins to form inside in the equatorial plane and goes to the periphery.

Mitosis - The main method of dividing eukaryotic cells, in which the doubling is first occurs, and then the uniform distribution between the daughter cells of the hereditary material.

Mitosis is a continuous process in which four phases are distinguished: proofased, metaphase, anatherapy and binding. Before mitosis, the cell preparations for division, or interphase. The period of preparation of the cell to mitosis and actually mitosis together make up mitotic cycle. Below is given a brief description of Phase cycles.

Interfhaza Consists of three periods: the pretenttical, or postmitic, - G 1, synthetic - S, postsynthetic, or prematched, - G 2.

Presintic period (2n. 2c.where n. - the number of chromosomes, from - The number of DNA molecules) is the growth of cells, the activation of biological synthesis processes, preparations for the next period.

Synthetic period (2n. 4c.) - DNA replication.

Postsynthetic period (2n. 4c.) - Preparation of cells to mitosis, synthesis and accumulation of proteins and energy for the upcoming division, increasing the number of organoids, doubling the centrioles.

Prophase (2n. 4c.) - Dismantling of nuclear membranes, the discrepancy between the centrioles to different poles of the cell, the formation of the threads of the separation of division, the "disappearance" of the nucleols, the condensation of the two-terrometic chromosomes.

Metafaza (2n. 4c.) - Lining the maximum condensed two-terrometic chromosomes in the equatorial plane of the cell (metaphase plate), attaching the threads of the separation of division by one end to centrilas, to the other - chromosome centromer.

Anaphase (4n. 4c.) - division by two chromosomes on chromatide and the discrepancy between these nursing chromatids to the opposite poles of the cell (while chromatids become independent single chromatic chromosomes).

Bulphaz (2n. 2c. In each subsidiary) - decondsation of chromosomes, education around each group of nuclear membrane chromosomes, the decay of the filament of the division, the appearance of the nucleus, the division of the cytoplasm (cytotomy). Cytotomy in animal cells occurs due to the fission groove, in the plant cells - due to the cellular plate.

1 - PROFACE; 2 - metaphase; 3 - Anphasis; 4 - BELFAZ.

The biological value of mitosis. Substrainy cells formed as a result of this method are genetically identical maternal. Mitz ensures the constancy of a chromosomal set in a number of generations of cells. It is based on such processes as height, regeneration, clarity reproduction, etc.

- This is a special way to divide eukaryotic cells, as a result of which cell transition from the diploid state into the haploid. Meiosis consists of two consecutive divisions, which precedes a single replication of DNA.

First Meiotic division (Meiosis 1) It is called reduction, since it is during this division that a decrease in the number of chromosomes is haveed: from one diploid cell (2 n. 4c.) Two haploid are formed (1 n. 2c.).

Interfaz 1. (at the beginning - 2 n. 2c., at the end - 2 n. 4c.) - Synthesis and accumulation of substances and energy necessary for the implementation of both divisions, an increase in the size of the cell and the number of organoids, doubling the centrioles, the DNA replication, which is completed in Proofase 1.

Proofase 1. (2n. 4c.) - Disassembly of nuclear membranes, the discrepancy of the centrioley to different poles of the cell, the formation of the threads of the separation of division, the "disappearance" of the nuclei, condensation of the two-terrometic chromosomes, the conjugation of homologous chromosomes and crossliner. Conjugation - The process of rapprochement and intertwing of homologous chromosomes. A couple of conjugating homologous chromosomes called bivalent. Crossingrigner is the process of metabolism with homologous areas between homologous chromosomes.

PROFAZ 1 is divided in stage: leptoten (completion of DNA replication), zigoten (conjugation of homologous chromosomes, education of bivalent), pakhtene (cross hinge, peretrozing genes), diplloten (Identification of chiam, 1 oxogenesis block in humans), diacines (Terminalization of chiasm).

1 - leptoten; 2 - Zigoten; 3 - Pakhiten; 4 - diploten; 5 - Diacines; 6 - metaphase 1; 7 - Anphasis 1; 8 - BELFAZ 1;
9 - PROFAZ 2; 10 - metaphase 2; 11 - Anphasis 2; 12 - BELFAZ 2.

Metafase 1. (2n. 4c.) - Laying the Bivalent in the equatorial plane of the cell, attaching the threads of the separation of division by one end to centrilas, to others - to the center meters of chromosomes.

Anphase 1. (2n. 4c.) - a random independent discrepancy between the two-line chromosomes to the opposite poles of the cell (from each pair of homologous chromosomes, one chromosome moves to one pole, the other to the other), reconventionation of chromosomes.

BELFAZ 1. (1n. 2c. In each cell) - the formation of nuclear membranes around groups of two-terrometed chromosomes, the division of the cytoplasm. In many plants, the cell from Anaphase 1 immediately goes to Proofase 2.

Second Macy Decision (Meiosis 2) called equational.

Interfaz 2., or intercines (1N 2c.) is a short break between the first and second meiotic divisions, during which the DNA replication does not occur. Characterized for animal cells.

Proofase 2. (1n. 2c.) - Disassembly of nuclear membranes, the discrepancy between the centrioles to the different poles of the cell, the formation of the threads of the spindle of the division.

Metafaz 2. (1n. 2c.) - building two-line chromosomes in the equatorial plane of the cell (metaphaz plate), attaching the filaments of the separation of division by one end to centrilas, to the other - chromosome centromer; 2 Block of Ovogenesis in humans.

Anphase 2. (2n. 2from) - division of two-line chromosomes on chromatide and the discrepancy of these nursing chromatids to the opposite poles of the cell (while chromatids become independent single-chromatic chromosomes), reconventionation of chromosomes.

BELFAZ 2. (1n. 1c. In each cell) - decondsation of chromosomes, formation around each group of nuclear membrane chromosomes, decomposition of the fission vertene, the appearance of the nucleus, dividing the cytoplasm (cytotomy) to form four haploid cells as a result.

Biological meaning of meiosis. Meiosis is a central event of gamenenesis in animals and spores in plants. As the basis of combinative variability, meyosis provides genetic diversity of Games.

Amitosis

Amitosis - Direct division of the interphase nucleus by drying without forming chromosomes, outside the mitotic cycle. Described for aging, pathologically modified and doomed to death cells. After amitosis, the cell is not capable of returning to a normal mitotic cycle.

Cell cycle

Cell cycle - Life of the cell from the moment of its appearance before division or death. The mandatory component of the cell cycle is a mitotic cycle, which includes a period of preparation for division and actually mitosis. In addition, in life cycle There are rest periods, during which the cell performs the function peculiar to it and elects further fate: death or refund to the mitotic cycle.

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Mitosis - This is a method for dividing eukaryotic cells, as a result of which 2 subsidiaries are formed, which have the same set of chromosomes, and the maternal cell.

During mitosis, one cell division occurs, which consists of four phases: profases, metafases, anafases and bodies. A set of chromosomes in cells before separation and after separation of the diploid. The state of hereditary information after separation is unchanged. Mitz in plant cells was opened in 1874 by I. D. cleanyakov, and in animal cells, mitotic division was discovered several later - in 1878 - V. Fleming and π. I. Vl.

phase mitosis

PROFAZ - Spiralization phase of two chromosomes. The following processes occur in the Proofase:

■ spiralization (condensation), that is, shortening and thickening of two chromosomes;

■ the differences in the centrioles to the poles;

■ decrease and disappearance of nucleoli (nuclei)

■ disintegration of nuclear shell fragments;

■ Formation veteen division - Microtubule systems in a cage that is divided. Provides chromosomes in mitosis and meyosis. The separation of the division contains two types of microtubes: those that depart from poles (pole) and from the center of chromosomes (chromosomal). Chromosome discrepancies occurs as a result of the reduction of chromosomal microtubes. Relieved divisions together with the centers of collecting microtubules forms a mitotic apparatus.

Metafaza - phase of the location of two chromosomes in the cell equator. In the metaphase chromosomes are located at the equator

I-III- prophase; IV- metaphase; V-VI - Anphase; VII-VIII.- bulfase.

cells at an equal distance from the core poles in the same plane forming the so-called methaphaz plate. It is important to note that they remain in this position for quite a long time. In connection with this, the metaphase is convenient for counting the number of chromosomes in the cell.

Anaphase - phase differences in single chromosome chromosomes to cell poles. In the anatherapy chromosomes are divided into separate chromatids and diverge to the poles of the cell.

Bulfase - The phase of desponderation of single chromosomes. It is also called "opposite on the contrary," because processes occur, which are opposite processes of processes: despondivization single chromosomes, the location of the centers in the nucleus, the formation of the nucleoli (nuclei), the formation of a nuclear shell and the destruction of the separation of division.

The biological value of mitosis: 1) provides accurate distribution of hereditary material between two subsidiaries; 2) ensures the constancy of the karyotype with a reproduction mileage; 3) underlies the crucible reproduction, regeneration, growth.

Biology +.Colchicin - Alkaloid, which has a strong antimottic effect. This compound suppresses the formation of filaments of mitotic spine of division, preventing it from a break from the tubulin protein subunits. Colchicine is used in biology to study the karyotype and for clinical diagnostic chromosomal anomalies, in breeding for obtaining polyploid forals, in medicine to reduce pain in the gout and others. Get colchicin from the squares of the unscrew-free (Colchicum Autumnale L.) which refers to the Melanhya family of Liliece. A non-lunist is very poisonous, but at the same time important medicinal plant And an interesting decorative plant.