A number of mutations have been described in G proteins, such as Ras, that have profound effects on their activity. For example, some mutations greatly increase the affinity of the G protein for GDP, making it very difficult for GDP to be exchanged for GTP. Other mutations prevent the hydrolysis of GTP to GDP. Which of the following scenarios would still result in a proliferation signal via the kinase cascade in the absence of ligand binding to its receptor kinase?
A)a continuously active receptor and an inactive Map kinase pathway
B)a Ras molecule that has no GTPase activity
C)a continuously inactive MAP kinase pathway and an inactive Ras protein
D)a continuously active Ras protein and an inactive MAP kinase pathway
E)a continuously activated receptor in the absence of ligand

Question

Quizplus · Accepted Answer

A Ras molecule that has no GTPase activity would continually be in the active GTP-bound form and would continuously activate downstream kinases, leading to a proliferation signal via the kinase cascade. The other scenarios either have an inactive MAP kinase pathway or an inactive component, which would prevent signal transduction and inhibit proliferation.

A Number of Mutations Have Been Described in G Proteins