Now it's the dark and the light purple alpha helices that we call the membrane spanning alpha helices. And that's because these are the regions of the protein which are found within that hydrophobic core of the membrane. They essentially anchor. They attach that entire structure of the protein into that hydrophobic core of the membrane. And so four of these identical polypeptide chains come together to form a tetrimer structure that looks like a cone. And that's because on one side of that cone we have a larger opening than on the opposing side of that protein.