Now, before the epinephrine actually binds to this section here, this is what it looks like. So notice on the intracellular side, we have a heterotrimer structure. And what that means is we have three different domains that create a trimer attached onto this seven TM domain. On the inside portion, of that structure. So we have an alpha domain, a beta domain, and a gamma domain. Now, the alpha domain is actually a g protein itself.