G-protein-coupled receptors (GPCRs) are a large family of proteins found in cell membranes. They play a crucial role in transmitting signals from outside the cell to the inside, allowing cells to respond to various stimuli, such as hormones, neurotransmitters, and environmental signals. GPCRs are involved in many physiological processes, including vision, taste, and immune responses. When a molecule, known as a ligand, binds to a GPCR, it activates an associated G-protein inside the cell. This activation triggers a cascade of biochemical reactions, leading to a specific cellular response. GPCRs are important drug targets, with many medications designed to interact with them, influencing conditions like asthma, depression, and high blood pressure.