Introduction to Viruses

in this video, we're going to begin our introduction to viruses by focusing specifically on the general structure of viruses. And so first we need to recall from some of our previous lesson videos that we already defined viruses as obligate intracellular parasites, which recall just means that these viruses have to make their way into a host cell in order to replicate themselves. And these viruses, they serve as parasites because they actually harm the host cell as the viruses benefit themselves by replicating. And so these viruses that serve as obligate intracellular parasites. They will contain either D. N. A. Or RNA packed into a protein coat. And sometimes in some cases some viruses will also have a lipid envelope. Now the protein coat that a virus has is specifically referred to as a caps it. And so the caps it is the protein coat that a virus has. And that protein coat helps to protect the nucleic acids, either DNA or RNA from environmental toxins and enzymes. Now the term new clio caps, it is a term that specifically refers to the combination of both the nucleic acids of the virus. Once again, either DNA or RNA as well as the caps ID protein coat itself. And so when you're referring to both the nucleic acids and the protein coat, the caps it, we use the term nuclear capsule and then last here we have is spikes. And the spikes are referring to surface proteins on the virus that allow the virus is to bind uh to a specific host cell receptor in order to initiate infection. And so this term variance here is a term that refers to a complete virus particle that has been released from the host cell into the extra cellular environment or extra cellular space, which is really the space on the outside of a cell. And so occasionally you'll see this term variance which is just referring to viruses on the outside of a cell. And so if we take a look at our image down below, we can get a better understanding of what a typical structure of a virus could look like. And although the shapes of viruses can vary and we'll get to talk a little bit more about the different shapes viruses can take later in our course, here is an image that represents the general structure of a virus. And so what you'll notice is that the virus is over here and the virus consists of some kind of nucleic acid which is going to be the green squiggly here. And this nucleic acid could be either DNA or RNA, and then around the nucleus acid is going to be a caps ID. And the caps, it refers to the protein coat. And so you can see the protein coat is surrounding the nucleic acid and helping to protect the nucleic acid. And so when you're referring to both the nucleic acid as well as the caps ID, then we're referring specifically to the new clio caps it. And so this term nuclear caps, it refers to both the nucleic acid as well as the caps and protein coat. And of course, over here in these yellow uh structures, you can see that these are specifically referring to the spike proteins and the spike proteins are these surface proteins that help the virus bind to specific host cell receptors and it allows the virus to initiate an infection. And so these spikes play a really important role to allow viruses to enter into their host cell in order to replicate. And so this year concludes our brief introduction to viruses and the general structure of viruses, including the Cap City nuclear caps it spikes and this term variations and we'll be able to get some practice applying these concepts and learn more about viruses as we move forward in our course. So I'll see while in our next video.

in this video we're going to differentiate between enveloped and non enveloped viruses. And so recall from some of our previous lesson videos that some viruses have a lipid bi layer on the outside of their structure and this lipid bi layer that some viruses have is called an envelope. And so enveloped viruses of course are going to be viruses that have an outer lipid bi layer and this outer lipid bi layer or this envelope that these enveloped viruses have is usually obtained from the host cell that they infect usually as they exit the host cell. Now a matrix protein is what links the lipid bi layer or the envelope to the remaining nuclear capsule of the virus. And these enveloped viruses actually tend to be more susceptible to soaps and detergents. And that's because these soaps and detergents are capable of damaging that lipid bi layer or damaging that envelope. And so soaps and detergents can be really effective at making these enveloped viruses non infectious. And so it turns out that the COVID-19 virus that caused the COVID-19 pandemic is actually an enveloped virus, which is why washing your hands with soap can actually be so effective at limiting the spread of that disease. Now, non enveloped viruses on the other hand are sometimes referred to as naked viruses. And so these non enveloped viruses or naked viruses, they do not have an outer lipid bi layer, they do not have an envelope and so they only consist of a nuclear caps it. And so if we take a look at our image down below, we can get a better understanding of enveloped viruses and non enveloped viruses. And so notice on the right we're showing you an enveloped virus which can be symbolically represented as a letter inside of an envelope. And then on the right hand side over here we're showing you a non enveloped virus which can be symbolically represented as just a letter without the envelope. And so focusing in on the envelope virus. First on the left hand side again, the virus that causes COVID-19 which is called SARS Kobe to uh is right here and it is an example of an enveloped virus. And so what that means is in addition to its new clio caps, it which again consists of its nucleic acid and the caps and protein right here. It also has this outer lipid bi layer and this outer lipid bi layer is again referred to as the envelope. And so here we can label this as the envelope and the lipid envelope is linked to the nuclear caps. It by these specific pink proteins that you see throughout here. And these pink proteins are the matrix proteins. And so that's exactly what we discussed up above these matrix proteins link the lipid envelope to the nuclear capsules. And what you'll also notice is that in addition to having uh the envelope embedded in the envelope will be the spike proteins that the envelope viruses used to bind to the surface receptors of the host cell to initiate an infection. And there may also be other surface proteins as well in that uh envelope. And so you can see over here in this image, you can see that this represents the envelope and the spikes are pointing out of the lipid envelope. Now on the right again, we're showing you a non enveloped virus and once again they do not have a lipid bi layer. They do not have an envelope and they only consist of a nuclear caps. Id. And so again, this is the new clinic acid, either DNA or RNA. And the caps ID is going to be the protein shell and the spikes will be sticking out of the capsule for these non enveloped viruses. And so a classic example of a non enveloped virus is this a dino virus that you see over here on the right. And so this year concludes our brief introduction to enveloped and non enveloped viruses. And we'll be able to get some practice applying these concepts and continue to learn more about viruses as we move forward in our course. So, I'll see you all in our next video

in this video, we're going to introduce the three most common shapes of viruses. Now it turns out that viruses can actually have many different types of shapes but the three most common shapes of viruses are I cosa federal helical and complex. Now the eye cosa he drove viruses are not perfectly spherical but they do appear to be spherical under an electron microscope. And so they are spherical looking viruses but they actually consist of approximately 20 flat triangular sides. And so they give somewhat of an appearance of a soccer ball. And so notice down below, over here on the left hand side we're showing you the E. Cosa cathedral viruses and the specific shape that they have. And so notice over here they're showing you an example of a virus that has an eye Cosa general shape and that is the human rhinovirus. Now the second most common shape that viruses can take on are the helical shape. And so these are going to be cylindrical looking viruses whose capsules are arranged as its name implies in a helix and the helix is somewhat resembling a spiral staircase. And so if we take a look at our image down below in the middle, notice we're showing you a helical virus and notice that it takes on somewhat of a spiral type of shape here spiral staircase. And so an example of a helical virus would be the Ebola virus and then the third and final most common shape of viruses are going to be complex. And so as its name implies, these viruses are going to have a variation of complicated structures and these complicated structures can have multiple different shapes. And so an example of complex virus could be bacteria pages or just pages. And so if we take a look at our image down below right here on the right notice that we're showing you a virus with a complex shape such as a bacteria fage. Like what we see here. And what you'll notice is that it has uh components that have many different shapes such as these legs have a specific type of shape and the body here has a specific shape. And then of course the head here has a specific type of shape as well. And so when you have a variation of these complicated structures with multiple shapes, this would be a virus with a complex shape. And so once again here we're showing you an image of a bacteria fage with a complex shape. And so this year concludes our brief lesson on the three most common shapes of viruses. And once again we'll be able to get practice applying these concepts and learn more about viruses as we move forward in our course. So I'll see you all in our next video