cell cycle
cell cycle The sequence of stages that a cell passes through between one cell division and the next. The cell cycle can be divided into four main stages: (1) the M phase, which consists of mitosis (nuclear division) and cytokinesis (cytoplasmic division); (2) the G1 phase, in which there is a high rate of biosynthesis and growth; (3) the S phase, in which the DNA content of the cell doubles and the chromosomes replicate; (4) the G2 phase, during which the final preparations for cell division are made. Interphase consists of the G1, S, and G2 phases, which comprise about 90% (16–24 hours) of the total time of the cell cycle in rapidly dividing cells. The M phase lasts about 1–2 hours. A point is reached in the G1 phase, known as the restriction point, after which the cell becomes committed to passing through the remainder of the cell cycle regardless of the external conditions. See illustration. See also cyclin.
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cell cycle
