AP BIOLOGY

Detailed explanation-1: -The cyclin A/CDK2 complex terminates the S phase by phosphorylating CDC6 and E2F1, and drives the cell-cycle transition from S phase to G2 phase, and subsequently activates CDK1 by cyclin A leading the cells to enter the transition to M phase. Upon mitosis, CDK1 activity is maintained by the complex cyclin B/CDK1.

Detailed explanation-2: -Cyclins drive the events of the cell cycle by partnering with a family of enzymes called the cyclin-dependent kinases (Cdks). A lone Cdk is inactive, but the binding of a cyclin activates it, making it a functional enzyme and allowing it to modify target proteins.

Detailed explanation-3: -Cyclin-dependent Kinases (CDKs) CDK4 binds cyclin D at the G1S transition to activate it to phosphorylate the retinoblastoma protein (Rb). CDK2 binds cyclin E late in G1 and with cyclin A in S phase to mediate the G2M transition.

Detailed explanation-4: -The activities of cyclin-dependent kinases (Cdks) control all aspects of cell division, including entry into the cell cycle from quiescence, the G1/S phase transition, DNA replication in S phase, nuclear breakdown, chromosome condensation and segregation, and cytokinesis (1).