Question

Anaphase Promoting Complex (APC) is a protein degradation machinery necessary for proper mitosis of animal cells. If APC is defective in a human cell, which of the following is expected to occur ?

• A. Chromosomes will be fragmented
• B. Chromosomes will not segregate
• C. Recombination of chromosome arms will occur
• D. Chromosomes will not condense

Answer 1

The Correct Option is B

 The question pertains to the role and implications of a defective Anaphase Promoting Complex (APC) in the process of mitosis. Let's explore each option and deduce the correct answer:

1. APC's Role in Mitosis:
   • The Anaphase Promoting Complex (APC/C) is a crucial ubiquitin ligase in the cell cycle. It facilitates the transition from metaphase to anaphase during mitosis by targeting specific proteins, such as securing, for degradation. Securing inhibits separase, an enzyme necessary to cleave cohesin rings holding sister chromatids together.
   • When APC is active, it degrades securing, allowing separase to cleave cohesins, thereby permitting the separation of sister chromatids to opposite poles of the cell.
2. Analysis of Options:
   • Option A: Chromosomes will be fragmented
     • This is unlikely to occur due to a defective APC. Chromosome fragmentation typically results from ionizing radiation or failed DNA repair, not APC activity.
   • Option B: Chromosomes will not segregate
     • With APC being defective, securin would not be ubiquitinated for degradation, maintaining separase inhibition. As a result, chromatid cohesion would not be resolved, preventing the segregation of chromosomes during anaphase.
   • Option C: Recombination of chromosome arms will occur
     • Recombination is a relevant process during meiosis, not mitosis, and does not directly relate to APC functionality.
   • Option D: Chromosomes will not condense
     • Chromosome condensation occurs during prophase and is regulated by condensins and histone modifications, unaffected by the APC directly.
3. Conclusion:
   • Considering the role of APC in chromatid segregation during mitosis, the correct prediction for a scenario with a defective APC is the failure of chromatid segregation. Therefore, the correct answer is: Chromosomes will not segregate.