Final answer:
Cyclin-dependent kinases (Cdks) are regulated by cyclins, which tightly bind to them and help in advancing the cell to the next phase of the cell cycle. Cdks phosphorylate other proteins, activating them and changing their shape. The concentrations of cyclin fluctuate throughout the cell cycle, and Cdk inhibitors can block the progression of the cell cycle.
Step-by-step explanation:
Cyclins regulate the cell cycle by tightly binding to Cdks. To be fully active, the Cdk/cyclin complex must be phosphorylated in specific locations, which changes the shape of the protein and activates it. The proteins phosphorylated by Cdks play a role in advancing the cell to the next phase of the cell cycle. The concentrations of cyclin fluctuate, and different cyclin/Cdk complexes bind at specific points in the cell cycle to regulate different checkpoints.
Regulation of the cell cycle can also occur through Cdk inhibitors. These inhibitor molecules block the progression of the cell cycle until specific conditions are resolved. The block on Cdks by inhibitor molecules is only removed once the specific event that the inhibitor monitors is completed.