division of cells - a vital process in which one parent cell forms several subsidiaries, with the same genetic information as the parent cell.
life cycle of each cell is also called the cell cycle.This period can be identified stages: interphase, and division.
Interphase - during the preparation of the cells to divide.This time is characterized by enhanced metabolic processes, the accumulation of nutrients, RNA and protein synthesis and growth and increase in the size of the cell.In the middle of this period there is replication (doubling) of DNA.After this, the preparation for the division: double centrioles and other organelles.The duration depends on the variety of interphase cells.
After the preparatory phase begins division.Cells ekariotov there are several ways this proc
ess: somatic cells - mitosis and amitosis for sex - meiosis.
amitosis - a direct cell division in which chromosomes do not change their status, there is no division spindle, the nucleolus and the nuclear membrane is not destroyed.At the core of partition walls are formed or it pereshnurovyvaetsya division of cytoplasm occurs and as a result, the cell turns dual-core, with a further continuation of the process - multi-core.
indirect cell division is called mitosis.When it is formed of cells identical in their chromosome set with the parent and, thus, ensures consistency of a particular type of cells in a number of generations.Mitosis is divided into four phases: prophase, metaphase, anaphase and telophase.
In the first stage the nuclear membrane disappears, there is a helix hromasom formed division spindle.In metaphase chromosomes move to the equatorial zone of the cell, the thread spindle attached to the centromeres of chromosomes.In anaphase the sister chromatids chromosomes disperse the poles of the cell.Now each pole becomes the same chromosome as was in the original cell.Telophase is characterized by the division of the cytoplasm and organelles, chromosomes unwind, there is a nucleus and nucleolus.In the center of the cell membrane is formed, and there are two daughter cells are exact copies of the parent.
meiosis - the process of division of sex cells, which results in the formation of sex cells (gametes), containing half the chromosomes of the original.It is characterized by the same steps as for mitosis.Only meiosis consists of two divisions coming immediately after one another and the result is not 2, and 4 cells.The biological significance of meiosis - the formation of haploid cells that are connected again become diploid.Meiosis ensures constant chromosomes during sexual reproduction, and various combinations of genes contribute to an increase in the diversity of traits in organisms of the same species.
prokaryotic cell division has its own characteristics.So non-nuclear organisms first splits maternal DNA strand, followed by the construction of complementary circuits.During the division of the two formed the DNA molecule apart, and between them is formed by the diaphragm.The result is two identical cells, each of which contains one strand of the parent DNA and a newly synthesized.