Cell cycle regulation (cyclins, checkpoints) Original Scenario-Based Download PDF

Questions

1. 1.

   During an orbital habitat mission, researchers monitor a bioengineered cell line whose division is tracked with real-time fluorescent biosensors. When micro-vibrations destabilize the assembly of spindle microtubules, the cells arrest abruptly mid-division with condensed chromosomes that fail to establish stable bipolar attachment. Although intracellular concentrations of active cyclin B-Cdk1 complexes remain high, none of the cells proceed to separate their sister chromatids. Which molecular mechanism accounts for this cell cycle arrest at the spindle assembly checkpoint?

   • A) Inactivated cyclin D-Cdk4 complexes fail to phosphorylate the retinoblastoma protein, blocking transcription of enzymes needed for replication.
   • B) Inhibitory phosphorylation of Cdk2 by Wee1 kinase prevents the assembly of pre-replication complexes across the nuclear genome.
   • C) Accumulation of active p53 stimulates transcriptional induction of p21, which binds and inactivates G1/S cyclin-Cdk complexes.
   • D) Unattached kinetochores generate an inhibitory signal that blocks the anaphase-promoting complex/cyclosome (APC/C), preventing securin destruction and cohesin cleavage.