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: -When a cyclin attaches to a Cdk, it has two important effects: it activates the Cdk as a kinase, but it also directs the Cdk to a specific set of target proteins, ones appropriate to the cell cycle period controlled by the cyclin.

Detailed explanation-3: -1.1 Cdks, the cell cycle and cancer Cyclin A-dependent kinases 2 and 1 are required for orderly S phase progression, whereas cyclin B–cdk1 complexes control the G2/M transition and participate in mitotic progression [4].

Detailed explanation-4: -Cyclin/CDK complexes are known to regulate both mitotic and meiotic cell cycles. While some mechanisms are common to both types of cell divisions, meiosis has unique characteristics and requirements. During meiosis, DNA replication is followed by two successive rounds of cell division.

Detailed explanation-5: -How do they interact in controlling the cell cycle? The CDKs, or cyclin-dependent kinases, have enzymatic activity and phosphorylate multiple substrate molecules when activated by binding to the appropriate cyclin. Cyclins are regulators of CDKs and have no enzymatic activity of their own.