Duration of Cell Cycle

The duration of the cell cycle, and of each phase within it, differs between cell types and organisms - some embryonic cells complete a cycle in under an hour, while some specialised adult cells may take days or may not divide again at all. Table 7.2 gives measured phase durations for a typical proliferating human cell with a roughly 24-hour cycle: the first gap phase G1 lasts about 11 hours, the DNA-synthesis S phase about 8 hours, the second gap phase G2 about 4 hours, and mitosis (M) only about 1 hour. Adding these up shows that interphase (G1 + S + G2 = 23 hours) dominates the cycle, exactly matching the general rule that interphase occupies roughly 95% of the total cycle time while active division (M) is comparatively brief. Knowing these relative durations is useful diagnostically too - a population of dividing cell …