Animation 17.3 Checkpoints in the Cell Cycle
Textbook Reference: The Eukaryotic Cell Cycle, p. 656
In most cells, checkpoints in the cell cycle prevent a cell from entering one phase if the events of the preceding phase have not been completed. At the G1 checkpoint, the cell checks for damaged DNA. Arrest at the G1 checkpoint allows repair of the damage to take place before the cell enters S phase, where the damaged DNA would be replicated.
The S-phase checkpoint provides continual monitoring of the integrity of DNA to ensure that damaged DNA is repaired before it is replicated. In addition, the S-phase checkpoint provides a quality control monitor to promote the repair of any errors that occur during DNA replication, such as the incorporation of incorrect bases or incomplete replication of segments of DNA.
A DNA damage checkpoint in G2 also leads to cell cycle arrest in response to unreplicated or damaged DNA. This checkpoint prevents the initiation of mitosis until DNA replication is completed.
Another checkpoint, called the spindle assembly checkpoint, arrests mitosis if the chromosomes are not properly aligned on the mitotic spindle and therefore not organized for equal distribution to daughter cells.
These cell cycle checkpoints function to ensure that complete genomes are transmitted to daughter cells.