Final answer:
Cell cycle regulation involves internal cyclins and Cdks as positive regulators and Cdk inhibitors as negative regulators, with growth factors serving as external signals to initiate cell division. Proper regulation is critical to prevent conditions such as cancer.
Step-by-step explanation:
Regulation of the Cell Cycle
The cell cycle is regulated by both internal and external mechanisms. Internally, the levels of cyclins and cyclin-dependent kinases (Cdks), which are positive regulators, fluctuate in a predictable pattern to ensure proper progress through cell cycle checkpoints. These proteins trigger the cell's transition from one stage to the next and are subsequently degraded to allow the cycle to continue smoothly.
External signals such as growth factors can also influence cell division by interacting with the cell's surface and initiating division processes. Negative regulation mechanisms, including Cdk inhibitors, prevent cycle progression by blocking Cdks until specific cellular conditions are met. This ensures that cells only divide when it is safe and appropriate to do so, preventing issues like the uncontrolled cell division seen in cancer.