A neurotransmitter binds to part of the protein located outside of the cell. Schematic drawing of a G-protein– coupled receptor (right). Neurotransmitter binds either to sites outside the cell or in a “pocket” formed by protein domains that span the membrane. The G-protein that consists of three separate protein subunits (α, β, and γ, light blue) is associated with part of the protein inside the cell.

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Prepared: December 2008