The Retinoblastoma (Rb) Protein Blocks Cells from Entering the Cell

Question

The Retinoblastoma (Rb) protein blocks cells from entering the cell cycle by
A)phosphorylating Cdk.
B)marking cyclins for destruction by proteolysis.
C)inhibiting cyclin transcription.
D)activating apoptosis.

Accepted Answer

The Retinoblastoma protein (Rb) inhibits the transcription of cyclins, which are required for the progression of cells through the cell cycle. Without cyclins, the cell cycle cannot proceed, and cells do not divide. Rb does not phosphorylate Cdk, mark cyclins for destruction by proteolysis, or activate apoptosis directly.