The basic theoretical items of information

Mitotic cycle is a period of time that includes processes of preparing to cell division and cell division. Mitotic cycle lasts from division till division.

Mitotic cycle consists of two main stages: interphase and mitosis. The cell cycle is divided into four phases and designated by G₁, S, G₂ and M.

Interphase — an interspace between two mitosises. The cell is most active during interphase. A cell in interphase has a nucleus with a nuclear membrane and nucleolus, its chromatin forms an irregular network, and the cytoplasm has a division center with a centriole. Interphase is the phase in which cell grows and synthesizes genetic and other materials. There are tree periods of interphase: p resynthesis period, synthesis period, and postsynthesis period.

presynthesis period (phase) or the first growth phase (G₁) consists of processes, which prepare synthesis DNA. There are synthesis and augmentation of the contents RNA and protein. This is the longest phase and varies from 6 to 8 hours. Within G₁- period there is a checkpoint, or restriction point. When a cell is passing the checkpoint it gets the “decision” to go to s – phase, or to go out from mitotic cycle (figure 22.1).

synthesis or S period (phase) is characterized of synthesis DNA and reduplication of chromosome. In result the contents of DNA in a nucleus is doubled. This lasts for 5 to 6 hours.

Postsynthesis period (phase) or the second growth phase (G₂) — is stage of immediate preparation to mitosis. In a cell the energy (ATP) is collected. It is duplicates materials other than DNA, which will be passed over to daughter cells (for example proteins, RNA, ATP). And some structures are formed too (mitochondria, Golgi bodies and cytoplasmic inclusions). G₂ lasts 4 to 5 hours. There is checkpoint in this phase. All the cells, which have passed the checkpoint, have to enter to mitosis (figure 22.1).

Finally, when the cell shows clear signs of cell division, the finish of interphase comes and the mitosis (M or D phase) begins. M-Phase lasts for 60 minutes or more, at the end of which two daughter cells with equal genetic material and dowries are formed from the mother cell.

Cell cycle is a period of time from cell division to another division or cell death (ruin). During cell cycle cell not only is preparing to division, but executes specific functions too (figure 22.1). For instance some kinds of cells produce digestive ferments, another kinds of cells pass the nerve signals. This means that these cells came out of mitotic cycle and has gone to way of differentiation.

Дата добавления: 2015-11-16