The main way of division of nuclear cages (eukariot) - a mitosis. The mitosis is resulted by doubling of hereditary material and its uniform distribution between daughter cells. At animal cages the mitosis lasts 30-60 minutes, at vegetable - 2-3 hours. During a mitosis the cage kernel (kariokinez), and then cytoplasm shares at first (tsitokinez).
Instruction
1. The mitosis consists of four consecutive phases: pro-phase, metaphase, anaphase and telofaza.
2. Professional azadNA spiralizutsya; the twisted chromosomes can be observed under a microscope. Each chromosome has two hromatida united by centromery. Centrioli disperse to cellular poles. The microtubules departing from centrioly begin to form a division spindle skeleton. There is a gradual destruction of a nuclear cover.
3. MetafazaHromosoma are located centromer on the equator of a cage. The metaphase plate is formed of chromosomes. To a centromer of each chromosome division spindle threads are attached.
4. AnafazaParnyy hromatida of chromosomes are split and disperse to cage poles. Now at two poles of a cage identical hereditary material is located. That genetic information which was provided by a single copy in a cage prior to the beginning of a mitosis is doubled and placed on poles now.
5. TelofazaHromosoma are untwisted in long thread, process of a transcription (data recording) begins. The transcription is carried out due to synthesis of new proteins with the set structure. Construction of kernels and nuclear covers begins. The spindle of division disappears.
6. TsitokinezTsitokinez is a process of "division of inheritance" between daughter cells. Contents of a maternal cage - cytoplasm share. The animal cage at the same time near the equator has a banner. It goes deep until there is a division. And at a plant cell the intracellular cover is formed.
7. A role a mitosis mitozaznacheniye for life of organisms - reproduction of cages with an identical genokod. Without mitosis the normal development and growth of the organism consisting of a set of cages is impossible. Thanks to a mitosis, wounds heal and sexless individuals breed.
8. AmitozPomimo of a mitosis, exists also amitotic division - direct cell fission. Amitotic division meets, generally at reproduction of the growing old cages or cages pathological changes (for example, cancer cells). At amitotic division only the kernel shares, DNA does not double, hereditary material is distributed on daughter cells randomly. As a rule, the cages formed as a result of direct division are defective.