So let's take a look at the following paragraph and then let's look at a specific example of a secondary messenger system. So our complex of proteins usually contains a transmembrane protein that is found on the membrane of that cell, the receptor cell that contains a binding side for the ligand and the ligand is the first messenger molecule. Now, this binding side is usually found on the extracellular side of the membrane as in this case. So what happens is once our first messenger binds to our transmembrane protein, on the other side of that transmembrane protein we have other proteins attached as we'll see in just a moment. And once our first messenger actually binds to our transmembrane protein it causes the dissociation of one of these proteins and usually it's the G protein. Now, once our G protein detaches, it can go on and do several things.