GPCR

Guanine protein coupled reactions (GPCR's) are a type of G-protein linked receptors that detect molecule outside the cell and cause a cell response. Initially, the guanine protein is made up of three subunits, an alpha, beta, and gamma subunit. When a ligand attaches on the outside of the transmembrane protein a conformational change occurs and the GPCR can activate an associated G-protein by exchanging a GDP bound to the alpha subunit with a GTP. When the alpha subunit is phosphorylated it dissociates from the beta and gamma subunits, which stay together. Both sections, the alpha subunit and the beta-gamma subunit complex, are now able to act on effectors that the are proper for the received signal. This continues until the alpha subunit is dephosphorylated. When this happens, all three subunits are rejoined and the GPCR returns to a resting state.