The transmembrane domains

The transmembrane domains located within
the plasma membrane (1–7) consist for the
most part of hydrophobic amino acids. The
structure of the gene product corresponds to
the general structure of the gene (6). The different
domains are coded for by individual exons.
The DNA nucleotide sequences within functionally
similar domains are similar.
The seven-helix transmembrane motif occurs
in many receptors. The general structures of the
genes and of the gene products are very similar,
but they differ in their specificity of binding to
other functionally relevant molecules (G proteins).
They play a role not only as neurotransmitters
but also in the transmission of
light, odors, and taste.