AP BIOLOGY

Detailed explanation-1: -Cell cycle progression is regulated in part by the sequential activity of various cyclins. The cyclins are regulatory subunits that bind, activate and provide substrate specificity for their catalytic partner serine-threonine kinases, collectively called cyclin-dependent kinases (Cdks) (reviewed in refs. 8 and 9).

Detailed explanation-2: -Cyclins regulate the activity of their Cdk partners and also modulate their substrate specificity. More than 20 Cdk-related proteins and more than 11 cyclins have been identified in more complex eukaryotes, which has led to the concept that different cell cycle events are regulated by distinct cyclin-Cdk complexes.

Detailed explanation-3: -The central components of the cell-cycle control system are cyclin-dependent protein kinases (Cdks), whose activity depends on association with regulatory subunits called cyclins. Oscillations in the activities of various cyclin-Cdk complexes leads to the initiation of various cell-cycle events.