G protein-coupled receptors (GPCRs) are so named because of their regulation of an intracellular heterotrimeric complex made up of G alpha and G beta gamma subunits. Ligand binding to receptor stimulates the well-described exchange of GDP for GTP by G alpha. This activity lies at the apex of numerous signaling cascades induced by a range of different stimuli including light, odorants, amino acids, nucleotides, lipids, and peptides/proteins. GPCRs make up the largest family of integral membrane proteins and account for approximately 5% of all genes found in the human genome. Clinically, approximately 45% of modern drugs target GPCRs, underscoring the importance of having quality research tools to study their functions. G-Proteins can be classified by homologous structure and via common ligand subtypes.