Explain generaly how Cyclin and Cyclin Dependent Kinase (CDK) work to control the cell cycle.

Various cyclins are the regulatory proteins that associate with respective cyclin dependent kinases. The cyclin-cdk complex activate or inhibit the proteins required for specific stage of cell cycle by phosphorylation.

Explanation:

Cyclin-dependent kinases (Cdks) are the protein kinases that are involved in the regulation of the cell cycle. Cyclins are the regulatory proteins whose levels change during the cell cycle. Cyclins associate with their respective cyclin-dependent kinases to activate them. The cyclin-Cdk complex phosphorylates the enzymes and other proteins required for a particular stage of the cell cycle.

For example, the G1-cdk (the cyclin - G1 specific Cdk complex) allows the cell to enter from G1 to S phase while the G1/S-Cdk complex makes the cell to commit for DNA replication while the S-Cdk complex serves in the initiation of DNA replication. The M-Cdk complex makes the cell to enter the mitosis by phosphorylation of proteins required for various stages of mitosis. Cdks are not activated when not associated with cyclins.

When the cell is not prepared for cell division, phosphorylation of protein p27 is followed by degradation of the [proteins required for cell division. The protein p27 is one of the inhibitors of cell division.