DNA Damage in Apoptosis signaling pathway

Upon DNA damage, cell cycle checkpoints are activated to arrest cells at certain stage during cell cycle, which allow cells to have enough time to repair damaged DNA before resuming cell cycle. If repair is faulty or the cell is overwhelmed by damage, chances are that the cell will despair and be removed by apoptosis. It stimulates a sequence resulting in the cleavage of Bid in a manner similar to the binding of so called “death-receptors” or directly initiates the permeability transition of the mitochondrial membrane which leads the cytochrome c releases from the mitochondria to the cytoplasm. This cytochrome c in the cytoplasm associates with Apaf-1 in the presence of dATP or ATP, thereby forming the apoptosome and activating caspase-9 which activates the downstream effector caspases, such as caspase-3. The caspases convey the apoptotic signal in a proteolytic cascade, with caspases cleaving and activating other caspases that then degrade other cellular targets that lead to cell death.