Answer to Question #282173 in Cell Biology for hayrunisa

Question

The Ras protein functions as a molecular switch that is set to its “on” state by other proteins that cause it to release its bound GDP and bind GTP. A GTPase-activating protein helps reset the switch to the “off” state by inducing Ras to hydrolyze its bound GTP to GDP much more rapidly than it would without this encouragement. Thus, Ras Works like a light switch that one person turns on and another turns off. You are studying a mutant cell that lacks the GTPase-activating protein. What abnormalities would you expect to find in the way in which Ras activity responds to extracellular signals?

Answer 1

1. You would expect a high background level of Ras activity, because Ras cannot be turned off efficiently.

2. Because some Ras molecules are already GTP-bound, Ras activity in response to an extracellular signal would be greater than normal, but this activity would be liable to saturate when all Ras molecules are converted to the GTP-bound form.

3. The response to a signal would be much less rapid, because the signal-dependent increase in GTP-bound Ras would occur over an elevated background of preexisting GTP-bound Ras.

4. The increase in Ras activity in response to a signal would also be prolonged compared to the response in normal cells.