Cell Biology MCAT Practice Question
During mitosis, a checkpoint protein detects an unattached kinetochore on one sister chromatid pair. The cell halts progression to anaphase, and the spindle checkpoint complex remains active, sequestering CDC20. Hours later, the kinetochore becomes properly attached to spindle microtubules, and the checkpoint is satisfied. Which of the following molecular events directly precedes anaphase entry?
Answer choices
- APhosphorylation of retinoblastoma protein by cyclin-dependent kinases
- BUbiquitination and proteasomal degradation of securin and cyclin B
- CRelease of CDC20 from the spindle checkpoint complex and activation of the anaphase-promoting complexCorrect answer
- DDephosphorylation of cohesin proteins by protein phosphatase 2A
- EBinding of MAD2 to the outer kinetochore and recruitment of BUB1 kinase
- FPhosphorylation of p53 by ATM kinase and activation of p21-mediated cell cycle arrest
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