Question

During the G1 checkpoint, ______ binds and inactivates G1/S-Cdk and S\Cdk, resulting in G1 arrest.

Answer 1

The G1 checkpoint utilizes p21 to bind and inactivate G1/S-Cdk and S-Cdk, preventing cell cycle progression if conditions are not favorable; p21's action is enforced by a rise in p53 levels due to DNA damage.

Step-by-step explanation:

During the G1 checkpoint, p21 binds and inactivates G1/S-Cdk and S-Cdk, resulting in G1 arrest. The G1 checkpoint is crucial for ensuring that all conditions are favorable for cell division to proceed, including a check for any genomic DNA damage. If damage is detected, p53 acts to halt the cell cycle and initiates repair mechanisms, or triggers apoptosis if repair is impossible. Upon the rise in p53 levels, p21 is produced, which enforces the halt by inhibiting the activity of the Cdk/cyclin complexes. This ensures that the cell does not move into the S phase until it is safe to do so.