Final answer:
Ras, a G-protein, activates a MAP kinase signaling cascade by first activating RAF, which then phosphorylates MEK and subsequently ERK. Phosphorylated ERK enters the nucleus and influences cell division. Mutations affecting Ras GTPase activity can lead to uncontrolled cell proliferation and cancer.
Step-by-step explanation:
The process of activation of the MAP kinase signaling module by Ras involves several critical steps. The Ras protein is a kind of G-protein that plays a pivotal role in cellular signal transduction. Initially, the activation of Ras is triggered by the binding of a growth factor to its receptor tyrosine kinase (RTK), leading to Ras exchanging its bound GDP for GTP, becoming active.
Once active, Ras interacts with and activates RAF, a serine/threonine-specific protein kinase. RAF then phosphorylates MEK, which is a dual-specificity kinase, meaning it can phosphorylate other proteins on both serine/threonine and tyrosine residues. Subsequently, MEK phosphorylates ERK, a MAP kinase, which leads to the phosphorylated ERK translocating into the nucleus. Within the nucleus, ERK triggers a variety of cellular responses, including the expression of proteins that lead to cell division and proliferation.
Mutations in RAS that inhibit its GTPase function prevent the hydrolysis of GTP to GDP, causing the Ras protein to remain perpetually active. This anomaly leads to continuous signaling for cell proliferation without the normal regulatory mechanisms in place, which can result in uncontrolled cell proliferation and potentially cancer, as Ras activity is a factor in a significant number of cancers.