Answer:
CDK is inactive without a cyclin bound to it.
Step-by-step explanation:
CDKs are the cyclin-dependent kinases. These protein kinases serve to regulate the various stages of the cell cycle. Cyclins are the regulatory proteins. The levels of cyclins fluctuate during the cell cycle. Cyclins bind to respective CDKS to activate them. Unless cyclins bind to CDKs, these protein kinases are inactive. Cdk associates with cyclin and forms a cyclin–Cdk complex. For example, mitosis specific Cdk bind to cyclins and activated M-Cdk then activates the proteins that facilitate mitosis and inactivate the one that inhibits mitosis.