G protein (Gs)

G-proteins convert signals from one form to another, therefore they are transducers within a signalling pathway. G-proteins transduce signals by binding to other proteins on the plasma membrane and are able to turn themsleves off by GTP-hydrolysis, they bind guanosine diphosphate(GDP) or guanosine triphosphate(GTP). 

There are two types of G-proteins: monomeric and trimeric. Monomeric G-proteins transduce signals from enzyme linked receptors e.g. RAS proteins. Whereas trimeric G-proteins transduce signals from G-protein linked receptors and they consist of three heterologous subunits: alpha, beta and gamma.

The alpha subunit of a trimeric G-protein is a GTP-ase and binds GDP in resting state. Two examples of trimeric G-proteins are Adenylyl cyclase and Phospholipase C which pass information down the signallin pathway by producing second messengers. The Gs alpha subunit activates cAMP-dependent pathways my activating adenylyl cyclase. These signals that have been transduced from G-protein linked receptors mediate most physiological responses within the body to various stimulants including neurotransmitters, hormones and the environment.