Regulation of the cell cycle is dependent on cyclins and cyclin-dependent kinases (CDKs).The key factor that allows a cell to progress beyond the restriction point in G1 is
A) the presence of cyclin.
B) the absence of cyclin.
C) the presence of cyclin and CDK.
D) phosphorylation of RB by CDK.
E) the presence of external signals from growth factors.

Question

Quizplus · Accepted Answer

Phosphorylation of the retinoblastoma protein (RB) by CDK allows the cell to progress beyond the restriction point in G1, as it releases E2F transcription factors necessary for DNA synthesis.

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