The G2-to-M transition
What triggers a cell's entry into mitosis from G2?
Answer C: explanation for every choice
A
Cyclin B degradation late in mitosis lets the cell exit mitosis.
B
p53 halts the cell cycle in response to DNA damage.
C
Correct. Rising cyclin B binds CDK1, and the active complex phosphorylates targets that start mitosis.
D
Cytokinesis occurs at the end of mitosis.
TakeawayCyclin B–CDK1 drives entry into M. Its destruction drives exit.
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Reviewed 2026-11-05 by a medical student. Spot an error? Report it with question ID bb135.