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Current time:0:00Total duration:11:05

Virus structure and classification

Video transcript

our episodes are interesting because they are the robot hackers of microbiology and in this video we're going to learn about what exactly makes them so good at being robot hackers so let's think about the things that define viruses there's four things we're going to look at first they're really really small so size if a virus is about that big compared to that tiny virus this would be the size of a typical bacterium it is a hundred times larger than a virus if you can just imagine this being well it clearly didn't draw this large enough but you can just imagine that there's a hundred viruses across here and this would be a hundred times larger in a typical eukaryotic cell like our own human cells would pretty much not fit on this page you can kind of imagine since it's a thousand times bigger it would form a circle that just goes straight off on either end of this quarter circle that I've drawn kind of forming a full circle just going all the way around so we talked about size between viruses bacteria and our human cells but there's another aspect of size which is the size of viruses compared to each other and of course some viruses are larger than others and that's one way to tell different viruses apart some are super small and other ones are just small I could have drawn bigger and smaller dots that represent viruses now the next thing that you can tell viruses apart with is their their shape so think about these tiny little things being blown up we're just going to talk about why they look like they look and what causes them to be the shapes that they are so all viruses have this capsid it's a protein coat and they're all very unique shapes you can think of them as the Legos of these viruses Legos because they need these little building blocks called the caps immers to build their shape so I'm just built building them with these little blobs here that you can see on the screen and even though I haven't drawn this really well there are actually all the same size and all the same shape for that particular virus so each of these little things would be called a capsular and these capsules form these three really beautiful three-dimensional shapes so this looks kind of 2d but if you can imagine kind of like a six-pointed you know three-dimensional looking this kind of six-sided diamonds like shape is called the icosahedral configuration and there's also something that if you first look at it it looks kind of helical but again it's not form like this it's actually lots of little monomers that wrap around kind of like a helix and it looks actually more like a cylinder but this because it wraps around like that is called a helical shape and one other possibility is the spherical shape so this gray line that I've drawn is an envelope and it sometimes covers the capsid and I say sometimes because not all viruses have this envelope it kind of gives it an advantage that we're going to talk about later so any one of these options can be inside and if you could imagine since it's an envelope wrapping that protein coat in a circle this is the spherical shape like a ball so that's two of four things to distinguish viruses with now here's the third one this is also pretty straightforward it's just the genetic information contained in viruses the nucleic acid so there are actually four options so viruses are really cool because they can contain one type of nucleic acid in fact they only contain that type so you've seen double-stranded DNA before which is in most of your human cells you've also seen single-stranded RNA kind of like your messenger RNA but you probably haven't seen some single-stranded DNA or double-stranded RNA and this is pretty unique to viruses they're special because they contain one of these types of nucleic acids this is one of the ways to distinguish them so a virus can be a single-stranded DNA virus or a single-stranded RNA virus they cannot be both so that and that's why nucleic acids are that third category it distinguishes viruses from each other and the this genetic information can't just float around it actually is kind of packaged it's stored inside of the protein coat and because this is called a capsid and this is nucleic acid when they're put together to form that virus and I'm just going to simplify that a ekko Saheed or drawing into this kind of hexagon shape and let's just pretend it's a single-stranded RNA virus then this is called a nucleo capsid and again this might or might not be envelope this one here that I've drawn is non envelope because it doesn't have a created line surrounding it so now that we've gone over these first three basic ways to tell viruses apart size shape nucleic acid we can now go back and figure out why I said that viruses are robot hackers and that actually will give us the fourth way to tell viruses apart right so I'm just going to write here robot hack because if you look back at what we just talked about viruses are really small and they're made up of proteins and one type of nucleic acid they don't have organelles and that means they can't make ATP or energy for themselves and they can't really replicate then because they don't have organelles so that's one problem because all living things metabolize so that's the robot part and they sneak into larger cells that have organelles that they can take over to make copies of themselves so the official term for robot hackers in biology is obligate it absolutely needs to be inside a Cell obligate intracellular parasite tax and other things to survive and because it needs to do that you can probably guess now that the fourth way to tell these apart is by the type of host so one question people always ask is that well is a bacteriophage a virus or what is it so it's actually the name for viruses that infect bacteria and the ones that are infect eukaryotic cells for example us humans they're all different enough in size shape nucleic acid and disease that they cause that they they have some pretty famous names like pox virus or herpes virus or or private virus and there's so many more so these robot hackers pack in using some special methods that I haven't mentioned yet and they actually both have to do with shape adaptations which makes sense because that's the outside part of the virus that comes in contact with the cells because if they weren't good at getting into the cell they would have never make copies of themselves so as robot hackers they must do something special to get in and bacterial pages have this complex shape they are not just IKOS or helical they might have that initial that nucleo capsid at the top with the head portion that contains the nucleic acid but it also has a sheath acting like a needle that the nucleic acid can be shot down and a tail that attaches to the host bacteria so even though I've drawn it this way you can actually imagine it attaching to the bacteria like this because the tail will bind it and it will act literally like a needle to inject the bacteria and I'm going to use this eukaryotic cell as an example for this other shape cork that lets viruses get in because a eukaryotic cell that I've drawn here so larger just got this giant line of membrane for me to draw on and basically if it can't inject its genetic material like the complex virus then it sneaks in and I keep saying that but the reason I'm saying it sneaks is because every cell has receptors on its surface and these usually are regular receptors that cells need to communicate information to and from but viruses take advantage of that these receptors can't really tell the difference between normal signals or normal cells and a viral cell so this icosahedral or helical thing will come along and signal to these receptors and it'll trick the receptors into forming this pit and eventually it will bud off into an endosome and and it just kind of sits happily inside having sneaked in and you might recognize as endocytosis endocytosis entering the cell so so they made up this big fancy name for very simple it entered the cell with receptors receptor mediated endocytosis receptors end of zone and the sneaky reason as to why some cells have these these gray envelopes that I mentioned before to give them that spherical shape that just gives them an extra way in so they can also enter it with these receptor-mediated cytosis I'm just going to draw a gray dotted line around this one area so you can kind of imagine that yes if it had an envelope it could also enter this way but it has an extra option and that's because it already has this bubble so it it signals to the membrane hey I'm just going to fuse with you I'm going to combine with you and let myself in and they kind of got fancy with this name too and because it directly fuses with the membrane to let itself in it's called direct fusion and now you have a general idea of how to tell viruses apart and how they really are the robot hackers of the microbiology world