Which of the Following Most Accurately Describes a Cyclin

Question

Which of the following most accurately describes a cyclin?
A) It is present in similar concentrations throughout the cell cycle.
B) It is activated to phosphorylate by complexing with a Cdk.
C) It decreases in concentration when MPF activity increases.
D) It activates a Cdk molecule when it is in sufficient concentration.
E) It activates a Cdk when its concentration is decreased.

Accepted Answer

Cyclins activate a cyclin-dependent kinase (Cdk) molecule when they are present in sufficient concentrations. This activation triggers the progression of the cell cycle. Cyclins are not present in similar concentrations throughout the cell cycle and their concentration does not decrease when MPF activity increases. Cyclins complex with a Cdk to activate it, not phosphorylate it.