The following image depicts a G-coupled protein receptor, beta-adrenergic receptor protein, in the plasma membrane. An external signaling molecule ( epinephrine) binds to the GPCR and causes a conformational change. This change triggers interaction between GPCR and a nearby intracellular G-protein.  The G-protein is then activated and a dissociation of the G-protein subunit occurs. This results in subsequent reactions that ultimately lead to release of glucose into the blood stream during the fight or flight reaction.