Which of the following statements best describes a G protein? All G proteins

G proteins are membrane proteins that act as transducers by passing the signal conveyed to a receptor, a hormone, to an enzyme that is located inside the membrane. This enzyme then alters the concentration of a second messenger, which induces the required intracellular response. There are many different types of G proteins; the primary difference among them is found in the a subunit, rather than the or the y subunits. G proteins play an impoant role in signal amplification because one receptor can activate several G proteins, which in turn effects the activity of many enzymes, such as adenylate cyclase or phospholipase C. These G proteins are divided into three major groups defined by their effect. Gs proteins activate adenylate cyclase, raising cyclic adenosine monophosphate (cAMP) levels; and Gp proteins activate phosphalipase C, liberating inositol triphosphate and diacylgylcerol.