And that's why we have this structure shown here. The alpha domain is bound to these two domains as well as to that seven TM domain. So when epernphrine is not bound to the beta adrenergic receptor beta arm, the g protein binds guanosine diphosphate, GDP, and this keeps that trimeric domain intact and attached onto that seven TM domain, as we see in this diagram. But what happens when the epinephrine actually binds onto this location here? Well, as soon as that epinephrine binds, it creates conformational changes in this region of that seven TM domain, and that also creates conformational changes in the alpha domain. So essentially what happens is there's a constriction in the region that holds the GDP and that expels that GDP.