Animal Viruses: 2. Entry & Uncoating in the Host Cell

in this video, we're going to continue to talk about animal viruses and animal virus infections. By focusing on the second step of an animal virus infection which is entry into the host cell and uncoated within the host to and so after a virus has attached to the surface of a host cell, it can then begin the process of entry and uncoated NG. And so it turns out that enveloped viruses, which recall from our previous lesson videos are viruses that have an outer lipid envelope um can actually enter into their host cell in one of two ways. The first way is through membrane fusion and the second way is through end aceto sis now entry via membrane fusion is going to be when the outer lipid envelope of an enveloped virus fuses with the cells cytoplasmic membrane and so the cell cytoplasmic membrane ends up containing pieces of the viruses outer lipid envelope. And so if we take a look at our image down below, notice that the top half of our image here is focused on entry via membrane fusion and so notice that this only occurs here with enveloped viruses because enveloped viruses have an outer lipid layer and so the outer lipid layer here of the envelope virus is going to be able to fuse with the host cell cytoplasmic membrane. And so here you can see the fusion beginning to happen. And again the viruses outer lipid envelope is going to remain embedded within the cell cytoplasmic membrane as the virus enters into the cell without its outer lipid envelope. And so that is one way by which enveloped viruses can enter into a host cell. Now once again the second way by which uh enveloped viruses can enter into host cells via endo psychosis. And this is going to involve the mechanism of receptor mediated endo site oh sis which recall, we had covered receptor mediated and acidosis and some of our previous lesson videos. And so if you don't remember much about receptor mediated and acidosis, be sure to go back to our older lesson videos and check that out now, enveloped viruses can enter via either membrane fusion or end acidosis. However non enveloped viruses can only enter by endo cito sis And this is because non enveloped viruses do not have an envelope in a lipid layer and so they are not able to enter by member infusion. And so notice down below on the bottom half of the image here, we're focusing on entry via endo acidosis. And we're focusing specifically on a non enveloped virus. Because non enveloped viruses can only enter via and acidosis. However, again, enveloped viruses can enter via either membrane fusion or end of psychosis. And so what you'll notice is we have our non enveloped virus here which does not have its outer lipid envelope and so it is going to be able to enter into the host cell through endo psychosis, receptor mediated and acidosis and notice that it is going to become inv agitated by the cells cytoplasmic membrane. And so it enters into the cell as an end acidic vesicles. All and so notice that here the viruses within the host cell as an end acidic vesicles all, whereas up above here, the viruses within the host cell not within an end acidic vesicles. And so those are some of the differences between membrane fusion and end acidosis. And so we'll be able to actually talk more details about each of these entry processes as we move forward in our course. And we'll start off talking about entry via membrane fusion and then later we'll talk about entry via photosynthesis. And so that being said, I'll see you all in our next video.

in this video, we're gonna talk a little bit more details about the entry and encoding of enveloped viruses by membrane fusion. Which actually occurs in a series of a few steps that you can see down below in this image. And so we're going to analyze this image, starting at the left over here and making our way from left over to the right and so over here on the far left. Notice that we're showing you how the spike proteins on the virus is, what's going to be important to help bind uh the virus to the host cell receptor. Uh and so when it is binding here, that is going to be the very first step of a viral infection. And so what you can see here is that the spike proteins are going to be binding to the receptors on the host cell. After that, with membrane fusion, the viral envelope is going to fuse with the cell's membrane. And so notice that the viral envelope here is going to be fusing with this host cell cytoplasmic membrane. And so when that happens, only the new clio caps ID of the virus is going to enter. Remember the nuclear caps, It is just the protein coat with the nucleic acid. So only the nuclear caps it enters into the cell. And so you can see here that the nuclear caps it is here the protein shell with the nucleic acid on the inside that is the nuclear caps it the nuclear capsule will enter. However, the outer lipid envelope is fusing with the cell's membrane. And so it does not actually enter into the viral envelope, stays in the cell's membrane. And so you can see here the viral envelope is staying in the cells cytoplasmic membrane here. And so there are going to be components of the cell's membrane that are derived from that viral envelope. And uh the nuclear capsules that enters into the cell is going to begin to uncorked. And so the virus genome is going to be uncoated, which just basically means that it is going to be released. And so notice that we have the nuclear capsule right here which has the protein coat with the nucleic acid on the inside. And what happens is the protein coat is going to uncoated and so it is going to shed here and as it sheds the nucleic acid that was on the inside is released and now that nucleic acid can move on to the next step in an animal virus infection. And so this year concludes our brief lesson on entry and encoding of enveloped viruses by membrane fusion. And we'll be able to get a little bit of practice applying these concepts as we move forward and talk more about endo psychosis entry as well. So, I'll see you all in our next video

in this video, we're going to talk a little bit more about animal virus entry and uncoated by endo psychosis, which actually occurs in a series of steps that we're showing you down below in this image. And so we're actually going to analyze this image from the far left over here and making our way towards the right in that direction. And so of course, over here on the far left, we're showing you the very first step of an animal virus infection, which is the animal virus binding to the host cell. And so once again, the spike proteins on the animal virus are gonna help bind the animal virus to the host cell receptors. And so we're seeing the spike proteins here and despite proteins will bind to receptors on the host cell after this and end acidosis. Uh the process of receptor mediated end acidosis will actually begin. And so what you'll notice is that the host cell is going to form a membrane uh and an end acidic vesicles around the virus. And so you can see that here we have the virus and the host cell's membrane is forming an end acidic vesicles around it. Then the end acidic vestibule actually enters into the cell. And the end acidic vesicles contains the animal virus. Then at this point the virus is going to exit the end acidic vesicles along with any lipid layers that it has and then the virus genome is going to be on coated, which basically means it will be released. And so you can see here in this image that the virus nuclear caps it here is going to exit from the end acidic vesicles all and its lipid layers. And then after the nuclear caps it has exited, the nucleic acid is going to exit from the protein coat. And so you can see the protein coat here is uncoated and the nucleic acid is being released into the environment. And so once this nucleic acid is released and is available here within the cell's cytoplasm, then the next stage of animal cell infection, animal virus infection can take place. And so this year concludes our brief overview of animal virus entry and encoding by end acidosis. And once again, we'll be able to get a little bit of practice applying these concepts as we move forward. So I'll see you all in our next video.