The usual sequence of cell cycle -
Ans. is 'a' i.e., G0-G1-S-G2-M o In cell, the replication of the DNA occurs only at a specific time during the life of the cell. This period is referred to as the synthetic phase. The various phases of cell cycle are (in sequence) G0 - G1 - S - G2 - M.# G1: Presynthetic phase/interval.# S: Synthetic phase (DNA synthesis).# G2: Post synthetic phase/premitoic phase/interval.# M: Mitotic phase: Cells are produced which either directly reenter next cycle or pass into non proliferative G0 phase.# G0: Quiescent state.o There are two resting phases and two active phases in the cycle.# Resting phases -G1 & G2.# Active phases1) S-phase (synthetic phase) - As the name suggests, synthesis of new DNA takes place, i.e. doubling of DNA occurs.2) IM-phase (mitotic phase) - Mitosis takes place and the daughter cells recieve one copy of DNA. In this phase, cell number is doubled.o The duration of cell cycle and its stages varies greatly between cell types. The time taken for S, G2 and M phases are similar for most cell types, occupying about 6, 4 and 2 hours respectively whereas the duration of G1 shows cosiderable variation as short as 2 hours in rapidly dividing cells i.e. embryonic tissue or longer than 12 hours in some adult tissue. G1 phase is most variable because, in this phase cell are not committed to DNA replication, can enter resting state or progress to next cell division.o In mammals because of the time required for a cell to progress of S-phase through mitosis from begining is typically 12-24 hours irrespective of duration of G1 phase; almost all the variation in proliferating rates are attributable to the amount of time spent in G1/Go state.
G0-G1-S-G2-M
G0-G1-G2-S-M
G0-M-G2-S-G1
G0-G1-S-M-G2
DNA Replication 