And let's begin by examining the structure of an HIV agent. So this is what HIV looks like. We basically have this membrane shown in pink and on the membrane we have these embedded glycoproteins. Now, we have different types of glycoproteins. The two glycoproteins we're going to focus on in this lecture is a glycoprotein called GP 120 and glycoprotein called GP 41. So GP 120 is positioned on top of GP 41.