animal viruses behave differently than those bacteria fades. We just took a look at, in fact, just down to their structure. Animal viruses look different, so animal viruses tend to have viral envelopes, right. Those member Enis accessory structures that are often derived from the host cells own membrane. They also tend to have RNA genomes, unlike those bacteria fades that had DNA genomes. Now animal virus replication involves entry into the cell, just like we saw with bacteria fage. But this time the whole virus is going to enter the cell, and it's going to do that through cell surface protein receptor recognition. Right? So there are, you know, a variety of specific ways that this can happen. But think Endo site Asus. Think about those Endo site tot psychotic processes. We took a look at way back and cell signaling, and what happens there is you have little molecules wagons find to these cell surface receptors and that causes the membrane to fold inward and pinch in well similar to that these viral cell surface proteins they're gonna bind to receptors on the host cell and is going to cause the host cell to take the virus inside right. These viruses are very tricky. They trick the host cells. Uh, the viral RNA. Once inside the cell serves as a template for replication by the viral RNA polymerase so that RNA will serve as a template from which marinas will be synthesized by a special viral RNA. Polymerase retroviruses are a special type of animal viruses and these air viruses with RNA genomes that actually instead of just putting that RNA out there, thio make copies of Marna from it. Instead of doing that, these retroviruses actually do something called reverse transcription, Right? So transcription is when you take DNA and you copy over the message into an RNA code. But with these retroviruses do is they take their RNA code. That's their genome, and they turn it back into DNA, which they insert into the host cell's genome. So let's just cover that one more time. These viruses have an RNA genome. They reverse transcribed that RNA into DNA and then insert that DNA into the host cell's DNA genome. Now they use a special enzyme called reverse transcriptase. To do this, it's a special enzyme that can catalyze that RNA to DNA transcription. In fact, uh, because of the discovery of reverse transcriptase is we've actually been able to advance a lot of fields of biotechnology, these air, very helpful enzymes and much like we were talking about the Pro Fe Ages, which are those viral genomes inserted into the bacterial genome, right? Those precursor fage is more or less well when a retrovirus has inserted it's viral genome into the host cell's genome. Through that reverse transcription process, we call that a pro virus so pro virus very similar to pro fage, except to become a pro virus. You have to have this special reverse transcriptase enzyme. So in a way, pro viruses air kind of a little fancier than pro fage is now. We can see examples of this right here with a very famous virus. Human immunodeficiency virus, better known as HIV. HIV is an animal virus. It's also a retrovirus. It has a lipid bi, bi layer viral envelope accessory structure, and it has that reverse transcriptase enzyme. You can see it right here represented by this little blob right here, and it has an RNA viral genome. It interacts with this particular type of cell surface receptor, allowing its viral genome to enter the cell. And here we can see the steps of reverse transcription playing out whereby the viral genome is converted to DNA, that DNA is inserted into the host cell's genome, and from there viral products can be produced. And ultimately, the ultimate goal is to produce the proper viral products. To then create a new virus, which will leave the host cell taking some of its membrane with it to act as in viral envelope, and it will go infect a new cell. All right, let's turn the page.