Q.Describe the complete cell cycle, covering interphase (the G1, S and G2 phases) and M phase (karyokinesis followed by cytokinesis), and explain why interphase, despite showing no visible division, is often called the 'preparatory phase' of the cell cycle.
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Start your 14-day free trial to unlock the full solution →The cell cycle is the complete, ordered sequence of events a cell passes through between one division and the next, divided into interphase and M phase.
Interphase itself comprises three successive sub-phases. In G1 (Gap 1), the longest and most variable sub-phase, the cell grows, carries out its normal metabolic activities, and synthesises the proteins and organelles needed for growth, while its DNA remains as yet unreplicated. In S phase (Synthesis), the entire nuclear DNA content is replicated, so that each chromosome becomes duplicated into two identical sister chromatids and the cell's total DNA content doubles; in animal cells, the centriole also duplicates during S phase. In G2 (Gap 2), the cell undergoes a further period of growth and synthesises the specific proteins -- including spindle tubulin -- required for the mechanical process of division, completing its preparation.
M phase follows, comprising karyokinesis (division of the nucleus), which in a somatic cell most commonly proceeds by mitosis through the stages of prophase, metaphase, anaphase and telophase, followed by cytokinesis, the division of the cytoplasm itself, which produces two separate daughter cells. …
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