Question

Protein kinases that regulate the cell cycle and are only active when complexed with the protein cyclin are called ______.

Answer 1

Cyclin-dependent kinases (Cdks) are protein kinases that regulate the cell cycle only when complexed with cyclins, which fluctuate in concentration to activate the Cdks at certain checkpoints.

Step-by-step explanation:

Protein kinases that regulate the cell cycle and are only active when complexed with the protein cyclin are called cyclin-dependent kinases (Cdks). Cyclins regulate the cell cycle by binding to Cdks. For the Cdk/cyclin complex to be fully active, it must also be phosphorylated at specific sites. This phosphorylation changes the shape and activates the protein, allowing it to phosphorylate other proteins that are involved in advancing the cell through the next phase of the cycle. The levels of Cdks are relatively stable, but the concentrations of cyclins vary, initiating the formation of the Cdk/cyclin complexes at specific points of the cell cycle. This mechanism ensures the precise regulation of the cell cycle through various checkpoints.