![]() Receptors that bind protein ligands have a large extracellular domain formed by the part of the polypeptide chain shown in light green. In addition to their characteristic orientation in the plasma membrane, they have the same functional relationship to the G proteins they use to signal the cell interior that an extracellular ligand is present.Ī G-protein-linked receptor. They consist of a single polypeptide chain that threads back and forth across the lipid bilayer seven times and are therefore sometimes called serpentine receptors ( Figure 15-26). The same ligand can activate many different receptor family members at least 9 distinct G-protein-linked receptors are activated by adrenaline, for example, another 5 or more by acetylcholine, and at least 15 by the neurotransmitter serotonin.ĭespite the chemical and functional diversity of the signal molecules that bind to them, all G-protein-linked receptors have a similar structure. These signal molecules that activate them are as varied in structure as they are in function: the list includes proteins and small peptides, as well as derivatives of amino acids and fatty acids. G-protein-linked receptors mediate the responses to an enormous diversity of signal molecules, including hormones, neurotransmitters, and local mediators. elegans, for example, encode such receptors, and thousands have already been defined in mammals in mice, there are about 1000 concerned with the sense of smell alone. G-protein-linked receptors form the largest family of cell-surface receptors and are found in all eucaryotes. ![]()
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