Regulation of the cell cycle is dependent on cyclins and cyclin-dependent kinases. The key(s) that allows a cell to progress beyond the restriction point is (are)
A) Cdk1 and cyclin B.
B) cyclin D and p21.
C) cyclin A and Cdk2.
D) phosphorylation of RB by Cdk4 and Cdk2.
E) external signals from growth factors.

Question

Quizplus · Accepted Answer

The phosphorylation of the retinoblastoma protein (RB) by Cdk4 and Cdk2 is crucial for the cell to progress beyond the restriction point in the G1 phase, allowing the cell cycle to continue into the S phase.

Regulation of the Cell Cycle Is Dependent on Cyclins and Cyclin-Dependent