Question

Mitogenic signals control the levels of which cyclin to regulate passage through the R-point?

A

B

D

E

Answer 1

Explanation: The R point stands for restriction point. After this point is crossed no mitogens are needed for the progression of the cell cycle. Cyclin D and CDK4/6 are the molecules that cause the cell cycle to cross the restriction point, as these molecules cause the phosphorylation of the retinoblastoma protein (Rb), inhibiting it, allowing the transcription of genes needed for the synthesis phase by the releasement of the elongation factor E2F (released now by the inhibited Rb protein).

Answer: Cyclin D