Final answer:
The activation of M-Cdk is tightly controlled by the interaction of cyclins with Cdks and the phosphorylation which activates these complexes, enabling the cell cycle to continue. Cyclin levels dictate the formation and activation of these complexes, while Cdk inhibitors serve as checks to prevent premature progression.
Step-by-step explanation:
The activation of M-Cdk begins abruptly mainly because of the regulatory role of cyclins and their interaction with cyclin-dependent kinases (Cdks). To drive the cell cycle forward, cyclins need to bind to Cdks. This formation of a complex induces a conformational change upon phosphorylation, activating the kinases. These M-Cdk complexes are crucial for the cell to pass through different checkpoints and move to the next phase. However, the process is tightly regulated; without a specific concentration of fully activated cyclin/Cdk complexes, the cell cannot proceed.
Cyclin levels fluctuate and peak at specific times in the cell cycle, binding to stable levels of Cdk to form the active complex. Upon activation, M-Cdks phosphorylate various proteins instrumental in advancing the cell cycle, including entry into mitosis. Furthermore, the activity of Cdk/cyclin complexes is finely tuned by Cdk inhibitors that act as negative regulators. These inhibitors ensure the cell cycle does not advance until certain conditions are met, ensuring the proper progression and fidelity of cell division.