 TMV stands for Tobacco Mosaic Virus, and was discovered in the late 19th century. This was an infectious agent that attacked tobacco leaves, and again, the leaves in tobacco is what we get the tobacco from, so it's a disaster for tobacco growers. It was identified as an infectious agent, but it was much smaller than a bacterium, and at those days we didn't know what the virus was. It affects tomatoes, tobacco, and lots of other similar plants, and always the leaves, but again, it was first identified for tobacco. This was the very first virus to be discovered in the 1930s, and I think it was well, I'm not sure whether it was Wendell Stanley who discovered it, but Wendell Stanley was the first one to crystallize it in 1935, and so he first had to extract the material of the infectious agent, then they had to crystallize it, and then he was able to show that this consisted of protein and RNA, and that's about as far as they got, because they did not have a structure at the time, so some 20 years later, a researcher that you know was able to take the tobacco mosaic virus, not just crystallize it, but actually determine its structures, so if we're going from the TMV, here you saw a microscope image of it, this is a modern elxtone microscope image of it, again you see the length scale they're 50 nanometers, you see that there's some sort of long rod-like shape, but we don't know what the rod is yet. If we zoom in even more on this, we will get the structure that was determined by somebody you've heard of, Rosalind Franklin, in 1958. This is an example of a virus where you have a coat protein, a single coat protein, and then in red on the inside you have the RNA, which again is the genetic material of the virus that is delivered to the cell, and then used to make the cell produce even more virus, and this layer then, the reason why I have these rods is that the entire virus is just a repeating unit of tons of these small wedges basically, so you're going to need some sort of small wedge that we can repeat and put many copies of them next to each other. By now you can probably see the reason for this seemingly strange structure that has some loops, and that appeared to be twisted right. On the inside here we're gonna have less space, so we have to squeeze those four helices together there. On the outside we have more space and if anything we want to protect things, so here it makes sense that these longer loops, and here I need to stretch it out because I can't really fit the four helices there. Also if you're a virus you do not, you can't afford to waste genetic material like humans or something, you pretty much just express one protein. That is the single protein that is a repeating unit in the entire viral cape, and that RNA on the inside just codes for this protein. You see again when something occurs in nature, when something looks strange, there is a reason for it, and this is roughly how all viruses work. Some of them are more complicated and express many different proteins, that's certainly the case for the SARS-CoV-2 virus, we will come back to that later on in the class, but the fundamental principle is the same. A virus expresses the proteins that is going to tell the cell to produce more of, so we can hijack cells and form more viruses.