Final answer:
ATM kinase activation leads to phosphorylation of Mdm2 and separation from p53, resulting in p53 activation, which can induce apoptosis through Chk2 activation and inhibition of Cdc25 phosphatase if DNA damage is irreparable.
Step-by-step explanation:
In DNA damage-induced apoptosis, p53 recognizes DNA, which activates Chk2, which inhibits Cdc25 phosphatase. When a cell experiences DNA damage, a series of molecular events are initiated to either repair the damage or induce cell death. p53, a critical protein in this pathway, acts as a guard to maintain genomic integrity. Upon DNA damage, ATM kinase is activated which phosphorylates Mdm2 leading to its dissociation from p53. This allows p53 to become active and perform its function. The activated ATM kinase also phosphorylates Chk2 and the freed p53, further promoting the apoptotic pathway if DNA repair is not possible. p53 upregulates p21, which binds to and inhibits Cdk/cyclin complexes, halting the cell cycle and potentially leading to apoptosis. This prevents the replication of cells with damaged DNA and preserves the health of the organism by preventing the production of faulty proteins.