The D1 receptor is made up of a string of 446 amino acids folded to form a three dimensional protein embedded in the post-synaptic cell membrane. This string of amino acids weaves in and out of the post-synaptic membrane to form seven membrane-spanning domains. These transmembrane regions form a pocket which functions as the recognition site for dopamine molecules. More specifically, it is the third and fifth regions that are thought to be involved in transiently binding the neurotransmitter to the receptor. The extracellular loops of the structure are also thought to be involved in this ligand-binding action. It is the third intracellular loop of the protein, however, which serves as the binding-site for the G-protein associated with the receptor.