Final answer:
A mutant form of the Ras protein cannot hydrolyze GTP due to a mutation, leading to its permanent activation and causing an unregulated phosphorylation cascade that can result in uncontrolled cell proliferation, a hallmark of cancer.
Step-by-step explanation:
The product of a mutant Ras protein cannot hydrolyze GTP and functions independently of Receptor Tyrosine Kinases (RTKs). Normally, RAS protein is a G-protein that interacts with RTKs, initiating the MAPK kinase cascade, which regulates cell division and differentiation. In its active form, RAS is bound to GTP and, once it has completed its signaling function, it hydrolyzes GTP into GDP to become inactive again. However, mutations in the RAS protein can lead to an inability to hydrolyze GTP, leaving the RAS protein permanently active, even in the absence of ligand stimulation, making it a gain of function mutation. This results in a continuous activation of the downstream MAPK kinase pathway, leading to an unregulated phosphorylation cascade and potential uncontrolled cell proliferation, which is a characteristic of cancer.