Questions: Question 5 Which of the following statements best describes what happens to MPF during mitosis? The cyclin component of MPF is degraded. It is completely degraded. It is phosphorylated by a Cdk, which inactivates it. The Cdk component of MPF is degraded.

The answer is the first one: the cyclin component of MPF is degraded.

Explanation for each option:

1. The cyclin component of MPF is degraded.

   • Correct. During mitosis, the cyclin component of Maturation Promoting Factor (MPF) is ubiquitinated and subsequently degraded by the proteasome. This degradation leads to the inactivation of MPF, allowing the cell to exit mitosis.

2. It is completely degraded.

   • Incorrect. Only the cyclin component of MPF is degraded, not the entire complex. The Cdk (Cyclin-dependent kinase) component remains and can be reused in subsequent cell cycles.

3. It is phosphorylated by a Cdk, which inactivates it.

   • Incorrect. MPF is activated by phosphorylation, not inactivated. The inactivation occurs through the degradation of the cyclin component.

4. The Cdk component of MPF is degraded.

   • Incorrect. The Cdk component is not degraded; it remains intact and can be used again in future cell cycles.

Summary: During mitosis, the cyclin component of MPF is degraded, leading to the inactivation of MPF and allowing the cell to exit mitosis.