Question

Many mammalian tumors have mutations in the protein Ras, leading to uncontrolled cell division. Which of the following is false about Ras?

		The protein GAP inhibits Ras by inducing hydrolysis of GTP.
		Ras activation activates a kinase cascade.
		It is a monomeric G-protein.
		The protein GEF activates Ras by inducing phosphorylation of GDP.

Answer 1

The correct answer is the statement 4 is incorrect , about the Ras protein . which is ,The protein GEF activates Ras by inducing phosphorylation of GDP.

Statement 1 - Members of the Ras superfamily regulate many cellular processes. They are down-regulated by a GTPase reaction in which GTP is cleaved into GDP and Pi by nucleophilic attack of a water molecule . Hydrolysis of GTP to GDP causes the protein to become inactive.
Statement 2- Once Ras can activated,It can do a variety of things. In this example, it activates an enzymatic cascade of MAP kinases. This results in potent changes in the cell, such as the alteration of key proteins and changes in gene transcription.
Statement 3- The Ras superfamily G-proteins are monomeric proteins of approximately 21 kDa that act as a molecular switch to regulate a variety of cellular processes.
Statement 4 - Activation of the cell-surface receptor leads to the activation of Ras via guanine nucleotide-exchange factor (GEF), which binds to the Ras–GDP complex, causing dissociation of the bound GDP .