Final answer:
Ras is inactivated by hydrolyzing GTP to GDP, which regulates cell division. In certain cancers, mutations inhibit Ras's GTPase activity, leading to uncontrolled cell proliferation. This is because Ras remains permanently active, continuously promoting cell division.
Step-by-step explanation:
Ras, a small GTPase protein, is inactivated when it hydrolyzes bound GTP (guanosine triphosphate) to GDP (guanosine diphosphate). This process is essential for the regulation of cell division and signal transduction pathways such as the MAPK kinase cascade. In certain cancers, mutations can inhibit the GTPase activity of Ras, preventing it from hydrolyzing GTP to GDP, leading to perpetual activation of Ras and continuous cell division.
Mutations in Ras that affect its GTPase activity make it unable to switch off, resulting in unregulated propagation of growth signals and uncontrolled cell proliferation. This can lead to tumorigenesis, as Ras is persistently active and signalling for division even without the presence of growth factors.