Many G Protein-Coupled Receptors Contain Seven Transmembrane α-Helical Domains

Multiple Choice

Many G protein-coupled receptors contain seven transmembrane α-helical domains. The amino end of the protein lies at the exterior of the plasma membrane. Loops of amino acids connect the helices either at the exterior surface or on the cytosolic surface of the membrane. The loop on the cytosolic side between helices 5 and 6 is usually substantially longer than the others. Where would a coupled G protein most likely interact with this receptor?

A) at the amino end
B) at the carboxyl end
C) along the exterior margin
D) at the loop between H5 and H6