In this case we had two. We had our epinephrine was the first messenger or the primary messenger and a secondary messenger was our cyclic Amp. So once again, protein kinase A, the enzyme that thus farlates other proteins in the cell can be activated through a secondary messenger system. Now the first messenger is in this signal transduction pathway is the hormone also known as a neurotransmitter, in some cases is our epinephrine, also called adrenaline. It binds to a transmembrane protein called the betaandrinergic receptor and this causes a conformational change, a change in shape of this transmembrane protein which forces our alpha subunit, our G protein to change the GDP to GTP. This decreases definitive of our alpha subunit to this, this and this section.