Biology XI: 10 Cell cycle n division (1 Phases of Cell Cycle)

Phases of Cell Cycle Cell Cycle The sequence of events by which a cell duplicates its genome, synthesises other cell constituents, and eventually divides into two daughter cells. The events of the cell cycle are under genetic control. Phases of Cell Cycle Duration of the cell cycle varies from organism to organism, and from cell to cell. Duration of the cell cycle in humans is 24 hrs, and in yeast is 90 min. Phases of the cell cycle are: Interphase represents the phase during which a cell prepares itself for division, grows and DNA is replicated in it. Interphase occupies more than 95% of the duration of the cell cycle. It is divided into 3 phases − G1, S and G2. G1 (Gap1) phase is the phase between the end of mitosis and the initiation of DNA replication. The growth of the cell takes place in this phase. S (synthesis) phase is the phase of DNA replication. DNA content doubles (from 2C to 4C), but chromosome number remains the same. (remains diploid; 2n only). In this phase, the centriole also duplicates. G2 (Gap2) phase is the phase in which the proteins needed for mitosis are synthesised. Cell growth continues in this phase. G0 phase is the quiescent stage in which the cells that do not divide enter after exiting from the G1 phase. In this phase, the cells do remain metabolically active, but do not proliferate unless required. M phase represents the phase where the cell actually divides. It starts with nuclear division and ends with the division of the cytoplasm.