Question

PLEASE SELECT ALL CORRECT ANSWERS IN FIRST QUESTION AND ANSWER SECOND QUESTION. HIGHLY CONFUSED

Many Ras mutants are unable to hydrolyze their associated GTP molecules. How will expression of this type of Ras mutant impact downstream signaling? Select all correct Ras will always bind and activate Raf The cell cycle will arrest at the restriction point MAPK will never be phosphorylated Rb will always be phosphorylated Question 32 3 pts A cell expressing an Rb mutant whose amino acids normally phosphorylated by the G1/S Cdk are changed to asparagines and NOT expressing normal Rb is likely to: Arrest the cell cycle at the restriction point Divide in the absence of extracellular signaling Progress through the restriction point

Answer 1

# Ras will always bind and activate Raf.

# Rb will always be phosphorylated.

Hydrolysis of GTP by Ras is more importat for the deactivation of Raf. If the mutated Ras does not hydrolyse the GTP then, Raf remains active and it phosphorylates MAPK. This leads to cell cycle progression by phosphorylating Rb protein.

32. Arrest the cell cycle at the restriction point.

Phosphorylation of Rb is important for the progression of cell cycle. If the mutation brings asparagine to the phosphorylating site then, it can not be phosphorylated. This leads to the cell cyce arrest.