In this video, we're going to continue to talk about animal viruses and animal virus infections by specifically focusing on the 5th and final step of an animal virus infection, which is the release of the new viruses from the host cell. Now it turns out that this 5th step is actually a little bit different in enveloped viruses and non-enveloped viruses. And so in this video, we're going to focus on the release of enveloped viruses, and then later in a different video, we'll talk about the release of non-enveloped viruses. Once again, recall from our previous lesson videos that enveloped viruses are going to have an outer lipid envelope surrounding their nucleocapsid. It's important to note that most enveloped viruses are going to be released from the host cell by a process that's known as budding. Budding is the process that allows for the release of enveloped viruses by using the cell's cytoplasmic membrane to actually form the envelope itself. As we'll see down below in our image, the lipid envelope of an enveloped virus is actually derived from the host cell's cytoplasmic membrane. Now budding does not immediately kill the cell, the host cell, and so that is also important to note. If we take a look at our example image down below, we can get a better understanding of the release of an enveloped animal virus from a host cell. In this image, we're going to start over here on the far left, and we're going to make our way from left to right in that direction. So starting over here on the far left, notice that we're showing you a nucleocapsid of a virus that has assembled in the host cell cytoplasm. In order for this enveloped virus to eventually exit from the host cell, what needs to happen is the viral spike proteins are going to insert themselves into the cell's cytoplasmic membrane. You can see here these little yellow structures that are the spike proteins that are going to insert themselves into the cell's cytoplasmic membrane. Then what's going to happen is, the matrix proteins are going to begin to bind and the viral envelope itself is going to begin to coat the virion or the viral particle via those matrix proteins. Recall that the matrix proteins, which are shown here in pink, are the proteins that link the nucleocapsid to the viral envelope that is forming here. Notice that the viral envelope is forming from the cell's cytoplasmic membrane and budding of the cell's cytoplasmic membrane. Over here in this third image that you see, you can see that the nucleocapsid is going to be fully coated with the matrix protein. Notice that there is matrix protein all the way around here. Notice that the viral envelope, which has viral spike proteins, is also going to be surrounding the nucleocapsid. You can see the viral envelope with the viral spike proteins here as well. Ultimately what happens is the virion or the viral particle is going to be completely released from the host cell. You can see here we have the release of the virion or release of the viral particle, and it has its nucleocapsid along with its lipid envelope. It is a fully mature and a fully infectious virus. It is also important to note that occasionally, some viruses, some enveloped viruses, can actually obtain their lipid envelope from the cell's organelles. The envelopes can sometimes develop from a cell's organelle, like for example, it could develop from the Golgi apparatus membrane, or it could develop from the rough endoplasmic reticulum membrane, rather than the cytoplasmic membrane. The way that that would work is that the viral particle, the nucleocapsid, would bud into either the Golgi apparatus or the rough ER, and then through vesicles, it would be released into the environment. But either way, the enveloped viruses are going to be obtaining their lipid envelope upon being released from the cell. This here concludes our brief lesson on the release of enveloped viruses from the host cell, and we'll be able to get some practice applying these concepts, and then we'll talk about the release of non-enveloped viruses from the host cell. So I'll see you all in our next video.
Animal Viruses: 5. Release from Host Cell - Online Tutor, Practice Problems & Exam Prep
Release of Enveloped Viruses
Video transcript
Release of Non-Enveloped Viruses
Video transcript
This video, we're going to briefly talk about the release of non-envelope viruses from the host cell. Recall that non-envelope viruses do not have an outer lipid envelope, and they are going to be released from the host cell after the host cell has died by triggering a process known as apoptosis. Apoptosis is really just a complex mechanism of programmed cell death that can be initiated by the host cell as the host cell is carrying out an immune response against the infecting virus. Once the virus has been released from the host cell, the viral particles, of course, can then go on to infect other nearby healthy cells, restarting the entire infection process, starting with attachment, then shifting into entry and assembly, then synthesis and replication, assembly, and finally ending off with release.
In the image below, we're showing you an image of the release of non-enveloped viruses from the host cell. Notice over here on the far left, we're showing you these non-enveloped viruses. Again, these non-enveloped viruses are going to assemble on the inside of the cell in the cell's cytoplasm. Unlike enveloped viruses, which will be released and acquire an envelope through the cell's cytoplasmic membrane or another one of the host cell's membranes, here with non-enveloped viruses, the host cell is going to undergo changes in shape. It changes in shape during the early stages of the process of apoptosis. You can see the cell changes in shape right here. Ultimately, apoptosis, the process of programmed cell death, is going to occur. When the cell is programmed to die, the viral particles are able to escape and be released into the environment. Once again, the released viruses can go on to initiate a new infection in another neighboring cell.
This here concludes our brief lesson on the release of non-envelope viruses from the host cell, and we'll be able to get some practice applying these concepts as we move forward in our course. I'll see you all in our next video.
Which of these answers is a major difference between the release of enveloped viruses and the release of non-enveloped viruses?
All of the following descriptions of viral multiplication and viral nucleic acids are true except which of these answers?
All viruses must be able to do which of the following?
1. Kill the host cell.
2. Inject their viral genome into the host cell.
3. Lyse the host cell.
4. Have their viral genome replicated by the host cell.
5. Be able to reproduce in the absence of living cells.