G1/S checkpoint

The S phase is the point of no return in the cell cycle, and before a cell makes the final commitment to replicate, the G1/S checkpoint checks for DNA damage.

If DNA damage is present, the DNA repair machinery and mechanisms that arrest the cell cycle are put in motion. The delay in cell-cycle progression provides the time needed for DNA repair; if the damage is not repairable, apoptotic pathways are activated to kill the cell.

Thus, the G1/S checkpoint prevents the replication of cells that have defects in DNA, which would be perpetuated as mutations or chromosomal breaks in the progeny of the cell. DNA damaged after its replication can still be repaired as long as the chromatids have not separated.

See also

 molecular checkpoints

• cell-cycle checkpoints