Those Amazing G Protein Receptors by Frank Sherwin, M.A. * Using
freeze-fracturing and an electron microscope, researchers can
indirectly view the plasma membrane of a human cell. What is
revealed are large, globular protein molecules that stud the bi-
lipid membrane. These proteins are designed by the Creator to
receive chemical information such as hormones. One large group
of these cell surface proteins is called the G protein coupled
receptors (GPCRs) composed of seven membrane-spanning helices.
Receptors are proteins designed to process molecular signals.
GPCRs are divided into five major classes and "mediate an
extraordinary spectrum of cellular processes."1 For example,
they are involved with the reception of light energy packets
called photons resulting in our being able to see (these are the
rhodopsin-like receptors, belonging to class A of the GPCR
superfamily). Over one percent of the total mammalian genes are
represented by GPCRs. Hormones belong to a general group called
ligands, molecules that phy