How do cyclin-dependent kinases help regulate the cell cycle?

Question

What will be an ideal response?

Answer 1

As cells move through the cell cycle, readiness to progress from one stage to the next is regularly assessed. Numerous cell cycle checkpoints are monitored for cell readiness by protein interactions. A common mechanism for this monitoring is carried out by protein complexes that join a protein kinase with a second protein known as a cyclin protein. Protein kinases catalyze protein phosphorylation—the addition of a phosphate group transferred from a nucleotide triphosphate such as ATP or GTP to a target protein. Phosphorylation changes the conformation of target proteins and can either activate or inactivate the target protein. Protein kinases are usually present continuously in cells at relatively steady concentrations. Cyclin proteins, however, are so named because their concentrations are cyclic and linked to the cell cycle stage. Cyclin protein production is stimulated by growth factor proteins that are produced by other cells. The protein kinase components of these complexes are activated only when they associate with a cyclin; thus, the protein kinases are called cyclin-dependent kinases, or Cdks. In their activated state, cyclin–Cdk complexes phosphorylate numerous target proteins and regulate cell cycle progression at various checkpoints.