A particular cyclin called cyclin E forms a complex with Cdk 2 (cyclin-dependent kinase 2). This complex is important for the progression of the cell from G₁ into the S phase of the cell cycle. Which of the following statements is correct?
A) The amount of free cyclin E is greatest during the S phase.
B) The amount of free Cdk 2 is greater during G₁ compared to the S phase.
C) The amount of free cyclin E is highest during G₁.
D) The amount of free Cdk 2 is greatest during G₁.
E) The activity of the cyclin E/Cdk 2 complex is highest during G₂.

Question

Quizplus · Accepted Answer

The cyclin E/Cdk 2 complex is most important for the progression from G₁ to S phase, therefore it follows that the amount of free cyclin E (not bound to Cdk 2) will be highest during G₁ when the cell is making preparations to enter the S phase. Similarly, the amount of free Cdk 2 will be greater during the G₁ phase as it is available to bind with cyclin E to form the active complex. Therefore, options A, B, and D are incorrect. Option E is also incorrect as the cyclin E/Cdk 2 complex is most active during the G₁/S transition, not during G₂.

A Particular Cyclin Called Cyclin E Forms a Complex with Cdk