Final answer:
M-Cdk activity regulation is key in the cell cycle progression, where the phosphorylation of the Cdk/cyclin complex leads to the activation of phosphatases and further advances the cycle. The concentrations of cyclins, which bind to stable Cdk proteins, fluctuate to regulate the complex formation, critical for cell cycle checkpoints.
Step-by-step explanation:
Regulation of M-Cdk activity triggers a feedback loop because once the CDK is active, it can then activate more phosphatases. Cyclins and cyclin-dependent kinases (Cdks) are essential regulators of the cell cycle. Cyclins bind to Cdks, forming a complex that must be phosphorylated at specific points to be fully active. This phosphorylation of the Cdk/cyclin complex changes the protein's shape, activating it to phosphorylate other proteins and advance the cell to the next phase of the cycle.
The levels of Cdk proteins are stable, but the concentrations of cyclin fluctuate, determining when these complexes form. Various cyclins bind to Cdks at different checkpoints throughout the cell cycle. M-Cdk is a particular type of Cdk/cyclin complex important for the transition to mitosis (M phase). Positive regulation includes the cyclic fluctuations of cyclins, while negative regulation involves Cdk inhibitors, which prevent activation of Cdks until certain conditions are met for the cycle to proceed safely.