Multiple Choice
Which is the primary function of cyclins in the control of the cell cycle?
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16. Cell Division
Control of the Cell Cycle
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Which of the following statements best describes what happens to MPF (Maturation Promoting Factor) during mitosis?
A
MPF is only present during the G1 phase and is degraded before mitosis begins.
B
MPF activity is highest during the S phase and decreases as the cell enters mitosis.
C
MPF activity remains constant throughout the entire cell cycle.
D
MPF activity rises as the cell enters mitosis and then declines rapidly during late mitosis due to cyclin degradation.
Verified step by step guidance1
Step 1: Understand the role of MPF (Maturation Promoting Factor) in the cell cycle. MPF is a complex of cyclin and cyclin-dependent kinase (CDK) that regulates the progression of the cell through mitosis.
Step 2: Recall that MPF activity is tightly regulated by the levels of cyclin. Cyclin levels rise and fall during the cell cycle, which directly affects MPF activity.
Step 3: Note that MPF activity begins to rise as cyclin levels increase during the G2 phase, peaking as the cell enters mitosis. This high MPF activity triggers the events necessary for mitosis, such as chromosome condensation and nuclear envelope breakdown.
Step 4: During late mitosis, cyclin is targeted for degradation by the proteasome through ubiquitination. This degradation of cyclin leads to a rapid decline in MPF activity, allowing the cell to exit mitosis and return to the G1 phase.
Step 5: Based on this understanding, the correct description is: 'MPF activity rises as the cell enters mitosis and then declines rapidly during late mitosis due to cyclin degradation.' This reflects the dynamic regulation of MPF activity during the cell cycle.
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