Now, GP 120 is actually used to bind onto receptors on the target cell's membrane and GP 41 is used to stimulate the process of fusion of the membrane of the virus and the membrane of the target cell. Now, inside this membrane we have the protein capsule shown in brown and inside that protein capsite we have the contents of that virus. We have the genetic information, the RNA shown in red and we have two very important types of protein enzymes. One known as integrates. Let's suppose that's the blue one, that's the green one, and the other one is known as reverse transcriptase. Let's suppose that is our blue one and we'll discuss what their function is in just a moment.