Specifically, if the delayed S phase is caused by damage to DNA, does this mean that during the delayed part of the S phase there is no DNA synthesis whatsoever untill the DNA is repaired? I’m hearing differing accounts of this. Some text says DNA synthesis is attenuated when this happens, others, like wikipedia, say DNA synthesis happens before repair occurs:
In the S phase, a series of sensors would detect DNA damage or any abnormalities and trigger a response that temporarily arrest further celll cycle.
The cell would use the delay to repair the the damage rather than continuing to the next phase. If the DNA is damaged beyond repair, the checkpoint mechanism would transmit a signal that leads to the death of the potentially hazardous cell.
The DNA repair referred to in wikipedia would refer to the error in replication process during S phase.
DNA repair after replication always happens, but if the cell delays the S phase due to DNA damage it will repair it first, then continue. Look for p53, it is a major element in this ‘delay or die’ decision.