The Ras GTPase was first discovered as a gene that plays an important role in tr

Question

The Ras GTPase was first discovered as a gene that plays an important role in transforming normal cellsinto cancer cells. Although Ras is normally activated by a receptor tyrosine kinase (RTK), in many kindsof cancer the Ras gene has sustained a mutation that makes the Ras protein hyperactive. This mutantRas sends unregulated signals that drive cell proliferation and contribute to tumor formation. ActivatedRas binds and activates a MAP kinase kinase kinase (MAPKKK) called Raf, which activates a MAP kinasekinase (MAPKK) called Mek, which activates a MAP kinase (MAPK) called Erk.15. What kinds of mutations in the Ras gene could lead to hyperactive Ras?

I. Mutations that stimulate Ras to bind the Ras GTPase-activating protein

II. Mutations that decrease the ability of Ras to hydrolyze GTP

III.Mutations that block Ras binding to Ras-GEF

a. I

b. II

c. I and III

d. II and III

Explanation / Answer

Answer is option b.

Mutations decrease the ability of Ras to hydrolyzed GTP.

This is because in a tumor formation there would be uncontrolled cell growth. The Ras pathway is not off. It is continously open, which means there would be no hydrolysis of GTP to GDP by Ras. This generally occurs when ras pathway is in off situation.

Other than this there would be continuous switching on in the Ras pathway which includes the binding of Ras to GTP, Accelerated by GEF proteins and there would be binding of Ras to GTPase for hydrolysis to GDP which leads to switching off of the Ras pathway.

So my answer is option b.

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