And inside that capsid we also have different types of proteins. We have a specific type of protein known as reverse transcriptase, which is basically a protein enzyme that acts to transcribe RNA into DNA as we'll see in just a moment. Now, the HIV also contains the purple lipidrich layer and this purple lipid rich layer contains protrusions which are basically receptors which will bind to the protein receptors found on the cell membrane of the human cell. So in step number one, we basically have the HIV, the virus that approaches the cell membrane of our human cell. And in step two we have the binding process taking place. These purple protrusions basically bind to the receptors, the protein receptors found on the cell membrane and specifically they bind to the protein receptors called CD four and CCR four.