Question

What proteins control the cell cycle?

Answer 1

The cell cycle control system is based on cyclically activated protein kinases.

Explanation:

At the heart of the cell cycle control system, is a family of protein kinases known as Cyclin dependent kinases (CDK's). The activity of these kinases rises and falls as the cell progresses through the cycle.The oscillations lead directly to cyclical changes in the phosphorylation of intracellular proteins, that initiate or regulate the major events of the cell cycle.

The most important of Cdk regulators are proteins known as Cyclins. Cyclical changes in Cyclin levels results in the cyclic assembly and activation of the cyclin-Cdk complexes. This activation in turn triggers cell cycle events.

There are four classes of cyclins, each defined by the stage of the cycle at which they bind Cdk's and function:

1) G1/S-cyclin: bind Cdk's at the end of G1 and commit the cell to DNA replication.

2) S-Cyclins: bind Cdk's during S phase and are required for the initiation of DNA replication.

3) M-Cyclins: promote the events of mitosis.

4)G1-Cyclins: help promote passage through start or the restriction point in late G1.