A) Transition from G1 to S and G2 to M depends on the phosphorylation of certain key proteins by cyclin-dependent kinase or Cdk.
B) Cdk's must be bound with a specific cyclin to be active as kinases.
C) In humans, cyclin D-cdk4 triggers the G1-to-S transition, whereas cyclin B-cdk1 triggers the G2-to-M transition.
D) External control mechanisms involving growth factors and hormones can activate cells that are arrested or are cycling slowly.
E) The phosphorylation of retinoblastoma protein effectively inhibits cell division.
Best answer:
Answer by Carlitos
I don't' know! sorry :(
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