Final answer:
G-protein-linked receptors bind a ligand and activate an associated G-protein, which then interacts with an ion channel or an enzyme.
Step-by-step explanation:
G-protein-linked receptors bind a ligand and activate an associated G-protein. The activated G-protein then interacts with either an ion channel or an enzyme in the membrane. G-protein-coupled receptors have seven transmembrane domains and each receptor has its own specific extracellular domain and G-protein-binding site.