Activation of the RAS-MAPK pathway begins when a growth factor binds to a receptor tyrosine kinase (RTK) on the cell membrane. This interaction leads to the receptor's dimerization and autophosphorylation, creating docking sites for adaptor proteins like Grb2. Grb2 recruits the guanine nucleotide exchange factor (GEF) SOS, which facilitates the exchange of GDP for GTP on RAS, thereby activating it.
