Question

Cyclins bind to Cdk to stimulate their protein kinase activity and control phosphorylation of target proteins. Cyclins are rapidly degraded only after the active Cdk-cyclin complex has triggered the transition through a cell cycle checkpoint. True or False?

Answer 1

The statement is true; cyclins bind to Cdks to form complexes that initiate transitions through cell cycle checkpoints, after which the cyclins are degraded.

Step-by-step explanation:

The statement regarding cyclins and cyclin-dependent kinases (Cdks) is true. Cyclins indeed regulate the cell cycle by tightly binding to Cdks. Their concentration levels fluctuate and are crucial for the formation of active Cdk/cyclin complexes, which are necessary to trigger the transition through cell cycle checkpoints.

Once a checkpoint is passed, these cyclins are no longer needed and therefore get degraded. This degradation ensures that the cell cycle can progress in a one-way direction, preventing the reactivation of past checkpoints. Such precise regulation is crucial for proper cell division and the overall health of an organism.