Urology>>>>>Basic Science and Molecular Oncology
Question 2#

At which point of the cell cycle is p53 partially responsible for detecting genetic damage?

a. G1 phase
b. S phase
c. G2/Mitosis checkpoint
d. Mitosis
e. G1/S Checkpoint

Correct Answer is E


Answer E

DNA damage causes a number of protein-protein interactions that alter protein phosphorylation. Initial sensing of damage is picked up by ATM and ATR proteins. These send signals to phosphorylate CHK2, CHK1, p53, MDM2 and BRCA1, which in turn arrest the cell cycle at checkpoints until DNA damage is repaired. The phosphorylation of p53 proteins causes altered activity in the CDK-inhibitor p21 WAF, which results in G1/S checkpoint arrest. S phase arrest results from phosphorylation of NBS1 and SMC1 directly via ATM. G2/mitosis arrest results from phosphorylation of CDC25C via CHK2 and CHK1.