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Question #45264
The Question
A culture of mammalian cells, grown for several generations in a medium, is transferred to a medium. Simultaneously, a chemical inhibitor is added that specifically blocks the proteasomal degradation of licensing factors, preventing centriole duplication but leaving DNA polymerase activity unaffected. After a time equivalent to one complete cell cycle, the cells are subjected to CsCl density gradient centrifugation and karyotypic analysis. Which of the following accurately describes the expected results?
Options
- A.
A single intermediate-density DNA band is extracted, but the cells exhibit massive chromosomal nondisjunction during the M-phase due to an asynchronous centrosome cycle.
- B.
Only a heavy-density DNA band is recovered, as the intra-S-phase checkpoint completely halts DNA replication when centriole duplication fails.
- C.
Both heavy and light DNA bands are observed, and the cells undergo normal karyokinesis but fail at cytokinesis, leading to syncytium formation.
- D.
A single intermediate-density DNA band is formed, but the cells arrest permanently in the G1-phase, preventing any chromosomal segregation.
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Comparative_Analysis
Sharpen your ability to evaluate multiple scenarios and distinguish between competing potential answers.
Concepts Behind This Question
Centriole Duplication Timing|DNA vs Chromosome Content|Meselson-Stahl Density Gradient
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often falsely assume that the failure of one S-phase event (centriole duplication) mechanically halts the other (DNA replication).
This question forces the student to decouple the biochemical success of DNA replication (yielding a Meselson-Stahl hybrid band) from the mechanical failure of mitosis (nondisjunction due to missing centrosomes).
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Cell Cycle and Cell Division - Class 11 |
| Concept | Centriole Duplication Timing |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |