Mitosis


The kernel on the different phases of mitosis and interphase non-fissile core; g - d stage of prophesy; e - stage metaphases; e - stage anafazy; W and z - stage telepathy; and the formation of two daughter nuclei.

Mitosis (mitosis, indirect division) - the fission of the nucleus of human cells, animals, and plants with further separation of cytoplasm. In the process of fission of nucleus of the cell (see) distinguish several stages. In the kernel, in the period between cell division (interphase), the chromosomes (see) are usually represented thin, long (Fig., a)they intertwine threads; clearly the shell of the nucleus and the nucleus.
In the first stage of mitosis, the so-called prophase, chromosomes becomes clearly visible (Fig., g-d), they shorten and thickening, along each chromosome there is a gap separating it into two quite similar to each other part, making each chromosome is double. In the next stage of mitosis - metaphase the kernel of is destroyed, the nucleolus is dissolved and chromosomes are lying in the cytoplasm of the cell (Fig., e). All chromosomes are arranged in a single row on the equator, forming a so-called Equatorial plate (stage stars). Undergoing changes and the centrosome. It is divided into two parts, diverging to the poles cells, are formed between them strands forming a cone chromatine spindle (figure, D. E.). Chromosomes are located on the equator of the spindle. On stage anafazy discrepancy occurs split subsidiary of chromosomes to the poles cells. During the last phase of mitosis-telepathy (Fig., W and W) - is the restoration of the structure of the kernel, chromosomes are stretched and thinned, turning into a long, randomly located thread; around each group of children chromosomes formed shell, stands out nuclear juice, you receive a nucleolus, centrosome decreases, taking the form of small rounded bullock, chromatine spindle disappears (Fig., and). At the end of mitosis is the division of the cytoplasm in half (it usually occurs by simple banners). As a result, formed two daughter cells, each of which has the same (equal to the number of chromosomes maternal cells and chromosomes. In various organisms, there are some deviations from the above typical mitosis.
Cm. also the Cell, the Cytoplasm.

Mitosis (from the Greek. mitos - thread) - indirect cell division, consisting in uniform distribution twice the number of chromosomes between the two daughter cells produced (Fig.). During mitosis are two kinds of structures: chromosomes and chromatherapy apparatus, including cellular centres and the spindle (see Cell).
The first stage of mitosis - profesa - begins with the appearance in the cell nucleus thin threads chromosome (see). Each in a prophase chromosome consists of two chromatid, closely adjacent to each other along the length of one chromosome maternal cells, another newly-formed by reduplication of her DNA on DNA maternal chromosome interfaze (pause between the two mitoses). As you progress through prophesy is spiralizatia of chromosomes, so that they are shortened and thicken. By the end of prophesy disappears the nucleolus. In prophase is also the development chromating apparatus. In animal cells cell centres (centriole) cleave; around them in the cytoplasm there are zone of very refracting light (centrevery). These formations begin to diverge in opposite directions, forming by the end of prophesy two poles cells, which by this time often becomes a spherical shape. In the cells of plants of centriole missing.
Prometaphase characterized by the disappearance of the nuclear envelope and education in the cell fusiform filamentous structures (chromatine spindle), part of the thread which connects the poles chromating system (interesovalsya threads), and others - each of the two chromatid with the opposite poles of cells (idle threads). Chromosomes, lying randomly in a prophase in the kernel, start moving in the Central area of the cell, where in the Equatorial plane of the spindle (medicines). This stage is called the metaphase.
During anafazy discrepancy occurs partners each pair chromatid to opposite poles cells by reducing pulling the threads of a spindle. Since that time, each chromatid receives the title of the child chromosomes. Dispersed to the poles chromosome gather in compact groups, which is characteristic for the next stage of mitosis - telepathy. This chromosome is gradually despiralization, loosing dense structure; around them appears nuclear shell starts the process of reconstruction of cores. There is an increase in the volume of new nuclei, they acquire nucleoli (the beginning of the interphase, or a stage of "resting kernel").
The separation process of the nuclear substance cells mitosis is accompanied by a division of the cytoplasm (see) - cytokinesis. The cells of animals in telophase in the field of Equatorial zone appears hauling, which, venturing, led to the division of the cytoplasm of the original cells into two parts. The cells of plants in the Equatorial plane of small vacuoles endoplasmic reticulum cell is formed partition separating from each other, two new cell of the body.
To mitosis, in principle, close endomicas, i.e. the process of doubling the number of chromosomes in the cells, but without division of nuclei. After endomitosis can occur direct fission and cells, the so-called amicos.
Cm. also Karyotype, the nucleus of the cell.

Schematic illustration of the interphase nuclei and various stages of mitosis: 1 - the interphase; 2 - profesa; 3 - prometaphase; 4 and 5 - metaphase (4 - view from the equator, 5 - a view from the pole cells); 6 - anaphase; 7 - telophase; 8 - late telophase, the beginning of reconstruction of nuclei; 9 - daughter cells at the beginning of interphase; Yao nuclear envelope; YAK - nucleus; XP - chromosome; C - centriole; In - spindle.