Question

A number of mutations have been described in the G protein Ras that have profound effects on its 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 GTPase activity of Ras, preventing it from causing the hydrolysis of GTP to GDP. Which of the scenarios would result in a persisting proliferation response to growth factor receptor activation after the ligand is no longer binding to its receptor kinase? a mutation that blocks the exchange of GDP with GTP a mutation that blocks the GTPase activity of Ras Both a mutation that blocks the GTPase activity of Ras and a mutation that blocks the exchange of GDP with GTP would cause the response to persist. Neither a mutation that blocks the GTPase activity of Ras nor a mutation that blocks the exchange of GDP with GTP would cause the response to persist.

Answer 1

Answer:

a mutation that blocks the GTPase activity of Ras

Explanation:

A G protein in inactive state is GDP bound but as soon as a guanine exchange factor (GEF) exchanges it with GTP it gets activated which means that in GTP bound state it is active. G - protein has endogenous GTPase activity. Upon interaction of GAP, the GTPase activity of this protein is exhibited. When GAP is present, hydrolysis of GTP into GDP occurs which leads to inactivation of G protein. A mutation which will block GTPase activity of Ras will therefore result in constitutive active signaling even in the absence of ligand binding to it's receptor. In such scenario, GTP will not be hydrolyzed into GDP so signaling will be up-regulated.