Cyclin proteins are essential regulatory molecules that control the progression of cells through the cell cycle. They achieve this by activating specific enzymes called cyclin-dependent kinases (CDKs). The levels of cyclins fluctuate throughout the cell cycle, ensuring that the cell only progresses to the next phase when it is ready. Different types of cyclins are associated with various stages of the cell cycle, such as G1, S, and M phases. When a cyclin binds to a CDK, it triggers a series of phosphorylation events that lead to critical processes like DNA replication and cell division. This precise regulation is vital for maintaining healthy cell function.