About the Cell Cycle

The cell cycle proceeds, by a defined sequence of events that depend on one another, to distribute complete and accurate copies of genomic DNA to daughter cells. To maintain the integrity of the cell cycle, cells are equipped with checkpoints that monitor and repair damaged DNA. The G1 checkpoint occurs before initiation of DNA synthesis, and the G2/M checkpoint occurs before mitosis.

The figure below illustrates the primary DNA-damage checkpoints that occur at the G1/S interface (G1 checkpoint) and G2/M interface (G2 checkpoint). Normal cells depend primarily on the G1 checkpoint to repair DNA damage. However, about 90% of tumor cells lack a G1 checkpoint and depend on G2/M arrest to effect DNA repair.