Final answer:
Two crucial types of proteins, cyclins and cyclin-dependent kinases (Cdks), interact to regulate the cell cycle. Cyclins enable Cdks to phosphorylate target molecules, thus allowing cells to pass through checkpoints. Disruptions to their precise regulation can lead to uncontrolled cell division and cancer.
Step-by-step explanation:
Positive Regulation of the Cell Cycle
The cell cycle is advanced by the concerted actions of two types of proteins: cyclins and cyclin-dependent kinases (Cdks). Cyclins are produced in a predictable pattern throughout the cell cycle, with their levels fluctuating to enable the cell to proceed through the various checkpoints. Once a cell progresses to the next phase, the cyclins from the previous stage are degraded. Cyclin-dependent kinases, on the other hand, must bind to cyclins and become phosphorylated to be fully activated. In turn, active Cdks phosphorylate other proteins, allowing the cell to pass a checkpoint and move forward in the cycle.
These processes are tightly regulated, with increases in cyclin concentration being triggered by both internal and external signals. A precise balance between different regulatory proteins, including cyclins and Cdks, is crucial for the healthy progression of the cell cycle. If this balance is disrupted, for example, by mutations that prevent the proper regulation and degradation of cyclins, cells may continue to divide uncontrollably, which can lead to cancer.