Receptors cinProtein-Coupled Receptor Systems 5HTa serotonin R G protein- Cell Surface Multisubunit Ligand-gated lon channels GTP GDP Catalytic Activities: G Proteins: Effectors atawth factor tecentors Defined by Regulated by Cytoplasm a Subunits: composition TGFB-rec 1 adenyly cycase.t Ca2.currents guanylin recepto Nat exchange Cvtosoli Nucleus regulated by 所subunits: phospholipase CB Figure 2-1.Structural motifs of physiologice and their relationships to signaling pathways. Basic qualifications for a receptor For a molecule to qualify as a receptor,it must meet at least 3 criteria: 1.In a given sample,there is finite number of receptors (saturation of binding and effect) 2.Ligand binding is specific and can be competed off by a ligand of the same or similar structure(e.g., agonists and antagonists) 3.Binding kinetics is consistent with biological effect (concentration-and time-dependency)Basic qualifications for a receptor For a molecule to qualify as a receptor, it must meet at least 3 criteria: 1. In a given sample, there is finite number of receptors (saturation of binding and effect) 2. Ligand binding is specific and can be competed off by a ligand of the same or similar structure (e.g., agonists and antagonists) 3. Binding kinetics is consistent with biological effect (concentration- and time-dependency)