You are studying the signaling pathways suspected to be altered in a colonic carcinoma. You are particularly focused on the activity of the G-protein RAS in these cells. Your studies reveal that the RAS protein can bind GTP and become activated with the same efficiency as the RAS from normal cells. However, the rate at which the cancer cell RAS activity is decreased is 10 times slower than in normal cells. Which of the following proteins is most likely to be defective in the carcinoma cells, resulting in abnormal RAS signaling? A) a G_i-type G-protein B) a G_q-type G-protein C) a G_s-type G-protein D) a GTPase-activating protein E) a guanine nucleotide exchange factor

Question

Quizplus · Accepted Answer

The GTPase-activating protein (GAP) is responsible for increasing the rate at which RAS hydrolyzes GTP to GDP, thereby inactivating RAS. If the rate of RAS inactivation is slower in cancer cells, it suggests a defect in GAP function.

You Are Studying the Signaling Pathways Suspected to Be Altered