What role do cyclins play in the progression of the cell cycle?

Cyclins play a crucial role in regulating the progression of the cell cycle by acting as essential proteins that control the timing of cell division. They achieve this by binding to and activating cyclin-dependent kinases (CDKs), which are enzymes that drive the cell cycle forward. The cyclin-CDK complexes facilitate various cell cycle events, including DNA replication and mitosis, by phosphorylating target proteins that are vital for moving the cell through different phases. As the concentration of cyclins fluctuates throughout the cell cycle, they ensure that cells only proceed to the next phase when they are ready, maintaining order and integrity in cell division. This precise regulation is essential for preventing uncontrolled cell proliferation, which can lead to issues such as cancer.