Question

Of a Cyclin/CDK pair, what generally fluctuates during the cell cycle and what generally stays constant, the catalytic kinase proteins known as CDK or the regulatory partners known as Cyclins? Explain what happens to the activity of a CDK when its cognate Cyclin is available and binds to it. What happens to the various Cyclins during the cell cycle, when does each accumulate and when do they start getting degraded?

Answer 1

The levels of cyclins fluctuate, while the levels of CDK proteins remain relatively stable in the cell cycle. Cyclins bind to CDKs and activate them through phosphorylation. Cyclins accumulate at specific stages of the cell cycle and are degraded afterward.

Step-by-step explanation:

In the cell cycle, the levels of cyclins fluctuate while the levels of CDK proteins remain relatively stable. Cyclins are regulatory partners that bind to CDKs to form fully active complexes. When a cyclin binds to its cognate CDK, it activates the CDK by changing its shape through phosphorylation. The different cyclins and CDKs bind at specific points in the cell cycle to regulate different checkpoints. Cyclins accumulate at specific stages of the cell cycle and are degraded after the cell moves to the next stage.