Heterotrimeric G proteins are composed of α, β, and γ polypeptide chains. Usually, the α and γ chains are anchored to the inner leaflet of the plasma membrane by lipid anchors that consist of a fatty acid that is linked to a cysteine side chain by a thioester bond. , the binding of a signaling ligand leads to exchange of a molecule of GDP for a molecule of GTP, bound to the Gα subunit. Concurrently, the Gα subunit dissociates from the GβGγ subunit. This allows both the Gα and the GβGγ subunits to interact with other signaling molecules.There are multiple copies of the genes for the Gα, Gβ, and Gγ polypeptides in eukaryotic genomes. In the human genome there are at least 15 different Gα subunits, 5 Gβ subunits, and 10 Gγ subunits. Hence, there are potentially ~1000 different combinations of these subunits, with different possible physiological effects that depend on which G protein-coupled receptor(s) they become associated.