NEET BIOLOGY

Detailed explanation-1: -These periods of activity are separated by regulatory checkpoints at major transition phases. These checkpoints include G0/G1 which regulates the entry of a quiescent cell back into the cycle, G1/S, and G2/M.

Detailed explanation-2: -The main cell cycle checkpoints are the G1/S checkpoint, the intra-S checkpoint, and the G2/M checkpoint [60]. The transition through stages of the cell cycle is regulated by the action of cyclin-dependent kinases, which are key targets for modulations induced by different cellular stimuli, including DNA damage.

Detailed explanation-3: -G1 checkpoint is near the end of G1 (close to the G1/S transition). G2 checkpoint is near the end of G2 (close to the G2/M transition). Spindle checkpoint is partway through M phase, and more specifically, at the metaphase/anaphase transition.

Detailed explanation-4: -Cell cycle checkpoints are surveillance mechanisms that monitor the order, integrity, and fidelity of the major events of the cell cycle. These include growth to the appropriate cell size, the replication and integrity of the chromosomes, and their accurate segregation at mitosis.