Ras signalling Pathway
The Ras signalling pathway is the main pathway involved in the transduction of growth factor signalling. It involves the dimerisation and autophosphorylation of a receptor tyrosine kinase (RTK), located on the cell membrane, which is brought about by the binding of a ligand (signalling molecule) to the receptor site on the RTK molecule. This triggers the binding of an adaptor protein (Grb-2) to the phosphate group on the RTK, and to that adaptor protein binds a Ras GEF molceule (Ras Guanine Nucleotide Exchange factor) which becomes activated. This molecule facilitates the removal of GDP from a nearby Ras molecule (a monomeric G-protein), which is replaced by GTP, and this results in the activation of the Ras. This activated Ras causes a conformational change in a nearby MAP Kinase Kinase Kinase resulting in the activation of the molecule. Via the conversion of ATP to ADP, the MAP KKKase phosphorylates a MAP Kinase Kinase, which then phosphorylates a MAP Kinase. This enzyme then phosphorylates a protein, activating it, leading to a cellular response.