So now that we know what a signal transduction pathway is, let's actually take a look at an example that takes place inside our body. So in this lecture, we're going to focus on epinephrine signaling, the epinephrine signal transduction pathway. But before we actually get to that, let's discuss an important category of transmembrane proteins that are used as receptors by these signal transduction pathways. And these are known as the seven transmembrane helix receptors, or simply 70 M receptors. Now, the structure of these receptors basically consists of seven membrane spanning alpha helices, as shown in this particular diagram. So this is our phospholipid bilar membrane.