What happens when DNA damage is detected during the G2 phase?

When DNA damage is detected during the G2 phase, the cell activates a control mechanism known as the G2-M checkpoint. This checkpoint prevents the cell from entering mitosis until the damage is repaired. The proteins ATM (Ataxia Telangiectasia Mutated) and ATR (ATM and Rad3-related) first detect the DNA damage. They then activate Chk1 and Chk2 kinases, which block the activity of Cdc25 phosphatase. Normally, Cdc25 activates the Cyclin B-CDK1 complex, which is essential for starting mitosis. But when Cdc25 is inhibited, the Cyclin B-CDK1 complex stays inactive, so the cell cannot move forward. This delay gives time for DNA repair enzymes to fix the damage. If the repair is successful, the cell enters mitosis. However, if the damage is too severe and cannot be fixed, the cell activates apoptosis (programmed cell death) to destroy itself and avoid passing damaged DNA to new cells.







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