Final answer:
Cyclin binds to M-CDK as its levels rise during the G1 phase and peak in G2, triggering the transition into mitosis. The Cdk/cyclin complex must also be phosphorylated to activate the proteins advancing the cell cycle.
Step-by-step explanation:
Cyclin binds to M-CDK during the cell cycle to regulate progression through various checkpoints. This binding typically occurs at specific times to ensure proper cell division and regulation. Cyclin's levels accumulate gradually and bind to the M-CDK complex, which stands for Maturation Promoting Factor.
The complex of cyclin-dependent kinase (Cdk) and cyclin is necessary for the cell to pass through checkpoints of the cycle. During the latter phases of the G1 phase, cyclin begins to accumulate and continues to do so into G2. It binds to more and more Cdk subunits, peaking in concentration during G2, triggering the cell's transition into mitosis. Phosphorylation by another kinase fully activates the Cdk/cyclin complex, ensuring the cell advances to the next phase.