At the onset of mitotic Anaphase, which key molecular event triggers the synchronous separation of sister chromatids?
Answer and explanation
Correct answer: D. Activation of the anaphase-promoting complex (APC/C) leading to securin degradation and separase activation
- Step 1: Sister chromatids are physically held together along their length by ring-shaped cohesin complexes.
- Step 2: The anaphase-promoting complex (APC/C) acts as an E3 ubiquitin ligase, targeting the inhibitory protein securin for proteasomal degradation.
- Step 3: Once freed from securin, the active protease separase cleaves the Scc1 subunit of cohesin, permitting spindle tension to pull sister chromatids to opposite poles.
Answer
Activation of the anaphase-promoting complex (APC/C) leading to securin degradation and separase activation.
Why not the others: Phosphorylation of histone H1 promotes chromosome condensation in prophase; Polymerization of actin at the nuclear envelope does not trigger chromatid segregation; Dephosphorylation of nuclear lamina occurs late in telophase.
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