Based on the model of eukaryotic cell cycle regulation shown in the figure, which of the following best describes the effect of a drug that blocks the production of the mitotic cyclin?

Question

BlackTom AI · Accepted Answer

In this question, we are considering how blocking the production of the mitotic cyclin would affect the eukaryotic cell cycle as depicted in the model.
Option 1 suggests that the G1 cyclin would substitute for the mitotic cyclin and allow normal division. While cyclins can have overlapping roles in some contexts, the mitotic cyclin specifically triggers entry into mitosis by activating CDKs necessary for chromosome condensation, spindle formation, and progression through mitosis. G1 cyclins primarily drive progression through G1 and the G1/S transition, not mitosis, so this substitution is not accurate.
Option 2 states that DNA synthesis would be prevented. DNA synthesis occurs during S phase and is regulated by cyclins associated with S phase and the G1/S transition, not directly by mitotic cyclin. Blocking mitotic cyclin would not halt DNA replication itself; cells could still enter S phase and replicate DNA if the earlier regulatory signals permit, so this answer misattributes the control point.
Option 3 posits that the cell cycle would proceed uncontrollably and become cancerous. A block in mitotic cyclin production would more likely impede progression into mitosis rather than cause uncontrolled division. Loss of mitotic cyclin activity would typically arrest cells before or during mitosis, not promote uncontrolled proliferation, making this option inconsistent with how cell cycle checkpoints function.
Option 4 asserts that the cell would be prevented from entering mitosis, and the cell would stop dividing. This aligns with the role of mitotic cyclin in activating CDKs that drive the cell into mitosis. Without mitotic cyclin, the G2/M transition cannot be properly executed, leading to an arrest before or at the point of mitotic entry and a cessation of cell division. This explanation fits the mechanistic understanding of cyclin-CDK regulation and the checkpoint controls that ensure orderly progression.
Therefore, the reasoning above supports that blocking mitotic cyclin production halts entry into mitosis and stops division, whereas the other options either misinterpret the regulatory roles of different cyclins or predict effects that are inconsistent with the designated block on mitotic progression.

APBIO141-031 with labs S12 - CollegeBoard* AP Exam Prep: Multiple Choice

Based on the model of eukaryotic cell cycle regulation shown in the figure, which of the following best describes the effect of a drug that blocks the production of the mitotic cyclin?

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