Now, what happens once it makes its way into our cell? So let's suppose that our G protein coupled signal transduction pathway is actually turned on. And so what that means is this g protein is in its GTP phase and so it is bound onto the adenylate cyclase and it continually stimulates the cyclase to basically produce the camp, the cyclic adenosine monophosphate phosphates which stimulate the PKA. Now, in the absence of this catalytic A chain, this galphaprotein showed a red in the GTP phase, actually has a built in timer. And so it has Gtpa's activity. And that means it can itself turn itself off by using a water molecule to hydrolyze the GTP back into GDP.