| 00:00 | Welcome. This is the module on 13 where we cover viruses. In |
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| 00:06 | one, we're gonna cover a viral , uh the basics of a viral |
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| 00:11 | cycle. Um And uh how we them and then how we classify |
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| 00:17 | And the, and we'll talk a bit about uh specific life cycles of |
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| 00:22 | viruses which we call bacteria. In part two, we'll concentrate on |
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| 00:27 | life of animal viruses. OK. to begin a little bit uh about |
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| 00:33 | uh science perspective, OK. So obviously, as you can see, |
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| 00:39 | from the um figure with the you see the virus is of course |
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| 00:44 | a much smaller scale size. Uh picture of the virus on the far |
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| 00:52 | is the Ebola virus, which is among the more larger uh size range |
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| 00:56 | uh viruses. So viruses encompass probably um 20 nanometers to at the smallest |
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| 01:04 | nearly a um micron or 1000 nanometers the large end. OK. |
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| 01:13 | obviously, the size differences, of is because viruses exploit uh must have |
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| 01:17 | host cell in order to replicate. obviously, they have to get inside |
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| 01:21 | them. And replicate inside of hence their small size. If we |
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| 01:26 | uh bacterial uh types to viruses, is what that chart is showing you |
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| 01:32 | the group they are called and These are bacterial types that are what |
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| 01:37 | call um obligate inter of parasites. part of the lifecycle is actually that |
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| 01:44 | inside his cell. Uh and don't um can do a lot of |
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| 01:50 | So they part of their, their cycle and both of those cause disease |
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| 01:54 | they, that they infect cells. so your typical bacteria aren't, aren't |
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| 01:57 | that. And so you can kind think maybe because viruses are like |
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| 02:02 | they are obligate intra parasites and they require a host. And so you |
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| 02:06 | see in terms of uh intra or . Yes. For chlamydia viruses. |
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| 02:11 | . Typical bacteria. No. Uh plant a membrane. Uh of |
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| 02:17 | , the and chlamydia have all to their cells. So they, they're |
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| 02:20 | have of course, a lot in obviously with uh the typical bacterial |
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| 02:25 | OK? Because they themselves are bacteria well. They just happen to |
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| 02:29 | you know, on the smaller Um uh and, and are deficient |
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| 02:34 | some of their metabolic capabilities, but are protic cells. So, um |
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| 02:40 | of course, uh cannot replicate by . There's, there's no binary |
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| 02:44 | Uh They pass through bacteriological filters which tra bacteria, but viruses can flow |
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| 02:51 | reget and chlamydia depends some of them on, are on the smaller end |
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| 02:55 | size range. Um They uh vases are either gonna be DNA viruses or |
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| 03:04 | they gonna be RN a viruses? genomes. And so they, |
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| 03:07 | they won't have both types of nucleic in them. They don't have really |
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| 03:11 | kind of metabolism uh to generate uh nor can they carry a protein |
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| 03:17 | . So, um, but, know, you're not sensitive to antibiotics |
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| 03:22 | antibiotics can target it. Since viruses very few components in them, there's |
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| 03:27 | targets really for antibiotics. And so there, there are antiviral drugs that |
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| 03:33 | there, but no, there's no to, to, to combat a |
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| 03:37 | infection. So, um so let's a little bit about, talk a |
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| 03:43 | bit about discovery of viruses. um during the time they were |
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| 03:48 | of course, was when um the germ germ theory had been known |
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| 03:53 | a while. By that point, number of diseases were being characterized in |
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| 03:57 | of uh the bacterial agents of a of infectious diseases were being characterized. |
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| 04:02 | , um so when this study was on regarding um this infection of tobacco |
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| 04:09 | , which of course was a big during that time, um there was |
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| 04:14 | kind of infectious agent causing disease among plants. And so, in order |
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| 04:18 | study this, um they would uh and by study this uh looked at |
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| 04:25 | plants and compared to the healthy they could see uh the evidence of |
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| 04:30 | the disease state by the effect on leaves. So, uh it's obvious |
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| 04:35 | you look at the control of the leaves, there's quite a difference |
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| 04:39 | And so they took the, the uh plant leaves and crushed them |
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| 04:46 | Uh So him and I'm sure kind a buffer and um made an |
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| 04:52 | And so the idea of being if that's the diseased plant, then |
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| 04:56 | infectious agent should be in there and should be able to uh crush |
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| 05:01 | use form an extract filter, it the bacteria on top of the |
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| 05:05 | And now we've got our infectious OK. So, but when they |
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| 05:09 | that, they found that the um was so small it that the whenever |
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| 05:15 | tested the material on the filter and it to a healthy plant, the |
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| 05:20 | plant never came down with disease. again, this is using coked |
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| 05:24 | So, but when they looked at material that flowed through the filter that |
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| 05:28 | trapped, what we call the filk . When that was applied to the |
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| 05:33 | , then they saw the disease. they, when they discovered that they |
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| 05:36 | they were dealing with something that was , very, very small. |
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| 05:39 | Having pasture the filter. And it until a few years later uh with |
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| 05:45 | the development of the electron microscope because what you need to visualize viruses, |
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| 05:50 | microscope. That they weren't. Uh when they were first able to see |
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| 05:55 | these things look like. Then the mosaic virus, you see there is |
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| 05:58 | on a very small in range size , uh small end in terms of |
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| 06:04 | range, 20 nanometers. So, uh of course, viruses, as |
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| 06:10 | mentioned are, are parasites parasitic. you will, they, they require |
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| 06:13 | host cell, they must have the cell to do their functions, which |
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| 06:17 | course is to replicate themselves. Um gonna use the host materials to do |
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| 06:22 | . OK. Um Virtually every uh of every taxonomic group, uh |
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| 06:29 | plants, um zones, et All aren't, are have a particular |
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| 06:35 | that will infect them typically. Uh So they span the range. |
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| 06:41 | And so you see in terms of size range as well as I mentioned |
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| 06:45 | on the small end, 20 nanometers so to large end like Ebola, |
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| 06:49 | 1000 nanometers and everything in between and course, various sizes and shapes. |
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| 06:55 | of course, um you know, the last 10, 15 years or |
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| 07:00 | , it has become known that viruses thought to be really nothing, |
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| 07:05 | causing nothing but disease, there's actually , they're very ecologically important in a |
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| 07:10 | of ways uh found a very lots different environments. Um They, they |
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| 07:16 | a role in, in controlling populations of, of certain types. Um |
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| 07:23 | , and are, are have shown have you know, ecological importance and |
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| 07:26 | importance in our own microbiome in our as well. OK. OK. |
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| 07:32 | , and don't forget, you that viruses can also uh be the |
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| 07:36 | to transmit genes between bacteria as So remember the transduction uh phenomenon. |
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| 07:42 | um closest define more clearly. So defining viruses, they're, they're number |
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| 07:51 | , they're not cells. Hence the ace they obligate intracellular parasites, obligate |
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| 07:57 | they must have uh a host OK. Uh The structure. So |
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| 08:03 | structure of any virus is, is genome can be RN A or |
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| 08:08 | It won't be both, it'll be or the other um surrounded by a |
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| 08:12 | coat called the caption. OK. these captions will often have uh depend |
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| 08:17 | a vial type. This kind of uh shape. It's called the |
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| 08:22 | 20 sided polyhedron shape. Um The process of a life of a viral |
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| 08:31 | cycle is shown here. Now, gonna see that there's variations as we |
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| 08:34 | at different viral types. But this is the main thing that goes |
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| 08:39 | . So now, first and foremost the recognition of the virus to the |
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| 08:45 | . OK. And this of gonna be through peripheral proteins, glyco |
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| 08:50 | on the viral surface and on the cell surface, that's where the interaction |
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| 08:55 | and where it begins or ends. there's no recognition, then the virus |
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| 08:58 | not infect. So then um from host, uh of course, is |
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| 09:03 | be using things like DNA polymer. again, it all with viruses kind |
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| 09:07 | how they infect. And the nature their infection depends on really the genome |
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| 09:11 | have. So it's a DNA RN and that will determine what it will |
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| 09:15 | to, to carry out its Uh They will all need from the |
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| 09:20 | . RSS trn A nucleotides. Uh all the parts of the proteins they |
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| 09:26 | get from the host. Uh very they'll of course, use a, |
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| 09:29 | plea from the host. D A from the host but have asked asterisked |
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| 09:34 | because they can vary. Uh an A virus, for example, won't |
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| 09:38 | DNA plum. Um Certain RN A have their own particular RN A |
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| 09:44 | Uh some DNA viruses actually tear their DNA plumbers. So there is, |
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| 09:47 | , there's variation, OK. Um again, the viruses don't really have |
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| 09:52 | metabolism. They, they don't, don't have glycolysis or so respiration, |
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| 09:56 | they rely on the host for And so as a result, the |
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| 10:00 | the host, uh the, the of a virus infecting it and exploiting |
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| 10:05 | to replicate itself is going to take toll on the host in terms of |
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| 10:10 | and resources being uh taken from And so that of course, will |
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| 10:14 | the health of the host cell OK. And so if we look |
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| 10:18 | the basic cycle here, so the virus enters, OK. |
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| 10:23 | we'll see in some cases, the for animal viruses is very common for |
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| 10:26 | entire caps to enter the cell. bacterial virus is not so the geno |
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| 10:31 | the genome comes in. But regardless when the viral genomes has made it |
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| 10:36 | the uh has been exposed inside the , then copies of the genome can |
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| 10:40 | made. It may, some virus types will integrate into the host |
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| 10:47 | integrate their genome into the host chromosome become part of the host cell |
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| 10:52 | Um at some point though it will to replicate. And so it will |
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| 10:56 | copies of the genome and form what's the intracellular replication complex. So basically |
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| 11:01 | a virus producing factory inside the cell it will transcribe and translate viral |
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| 11:08 | Uh of course, then uh producing viral proteins and assemble uh the variances |
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| 11:14 | and viruses means the same thing. And so we'll form particles which will |
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| 11:20 | exit the cell. OK. And those can go on to infect other |
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| 11:26 | susceptible cells. Um The rate of production can vary by viral type. |
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| 11:33 | may some bacterial viruses can produce 100 200 or more viral particles per cell |
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| 11:39 | kill the cell. Others will produce particles at a very low rate. |
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| 11:46 | that will allow the actually will will allow the host cell to remain |
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| 11:50 | while the virus is producing uh bar at a very low rate. So |
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| 11:55 | cell can actually survive that process. others where the virus just integrates this |
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| 12:00 | and the, the host cell feels effects until it initiates a viral uh |
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| 12:05 | viral replication process. OK. So , the effect on the host can |
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| 12:12 | uh while it's, while it's affected the virus can be minimal, it |
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| 12:16 | be maximal and just basically kill it somewhere in between. So it's a |
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| 12:21 | as well and it depends on the viral type, in fact, |
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| 12:27 | a little bit more about structure. the caps the captures the caps, |
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| 12:30 | is the the structure that uh encloses the um viral genome uh convert in |
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| 12:38 | and shape. So I mentioned the shape, it can also form what's |
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| 12:43 | the helical uh form as you see like with Ebola. And so it |
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| 12:50 | forms kind of a filament. Uh capsid proteins surrounding the the genome is |
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| 12:55 | of a filament form rather than just 20 sided polyhedron. Uh The genome |
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| 13:00 | be, as I mentioned being it can be single stranded or double |
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| 13:04 | . Now, the difference between enveloped naked viruses. OK. So um |
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| 13:13 | a naked virus is one that of does not contain a, an |
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| 13:16 | A naked virus is basically a uh viral genome surrounded by a capsid and |
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| 13:21 | it. OK. There may be um molecules part of it captured, |
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| 13:28 | it's there's no surrounding envelope and and the envelope itself is acquired uh |
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| 13:34 | from the host cell as the virus the host cell. Ok. Um |
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| 13:41 | so you see there with uh whether a virus, um it the filming |
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| 13:48 | uh surrounded by an envelope or uh an influenza virus. Uh captured uh |
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| 13:56 | hero virus is. What influenza is is they get surrounded by an envelope |
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| 14:00 | well. OK? You may have multiple glycoprotein spikes. That's true, |
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| 14:07 | it's enveloped or or non enveloped um as you see there. So that's |
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| 14:12 | uh I think an antenna virus uh glycoprotein spikes uh as part of its |
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| 14:17 | caps. Uh it's one that's not , but envelope viruses can also have |
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| 14:22 | as well when they're present. Uh may be these, these are typically |
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| 14:26 | in the recognition and attachment to the cell. OK. So um the |
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| 14:37 | and so we look at uh complex , OK, such as a bacterial |
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| 14:44 | and bacterial viruses, which is what seeing here to even bacterial phage. |
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| 14:48 | , phage is a bacterial virus. bees are generally not enveloped, |
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| 14:52 | Because uh they don't uh generally bacterial just have a have the protein coat |
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| 15:01 | in this more complex structure where you it caps, but additionally, some |
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| 15:04 | parts to it like the sheath and fibers which again are part of the |
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| 15:09 | and binding to the host surface. The um activity. So, activity |
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| 15:19 | , as I mentioned is where it and ends in terms of the |
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| 15:23 | being successful and being able to replicate . And so, uh the course |
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| 15:28 | all about recognition between host and And again, it's gonna be surface |
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| 15:33 | , glyco proteins uh through certain types and the the there's other proteins there |
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| 15:42 | in the caps besides capsid proteins, can have like a protein spikes, |
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| 15:45 | could be other types of proteins in uh that recognize particular host surface moles |
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| 15:51 | can be receptors or uh other types uh surface molecules. So that, |
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| 15:58 | um recognition um is gonna be specific the virus will bind to it and |
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| 16:05 | that's how, how it will gain . Um So we talk about host |
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| 16:10 | . There's two two things here, host range which is how many different |
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| 16:16 | can the virus infect? OK. classic example there we we we can |
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| 16:21 | at in terms of broad and Is it a very broad, can |
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| 16:24 | a number of different host types or it very narrow? Ok. And |
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| 16:29 | is a typical example here. Um rabies can infect squirrels, cats, |
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| 16:34 | , humans, um different types of . So it different types of |
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| 16:41 | And um so obviously a very broad of hosts HIV it can only affect |
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| 16:47 | , no other type. And so obviously a very narrow range. Um |
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| 16:55 | uh uh Coronavirus, very narrow it only affects humans. Um The |
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| 17:06 | also exhibit tissue specificity. OK. this is a variation of host |
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| 17:14 | So, whereas host range is having host, it can effect. Tissue |
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| 17:21 | relates to here's a virus inside a host. How many different cell types |
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| 17:27 | infect? Ok. So let's just rabies virus. All right, rice |
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| 17:31 | affect, as I mentioned, different of mammals can be affected with |
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| 17:35 | But within a mammal, whether it's , a squirrel or a dog or |
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| 17:39 | human, it's only gonna infect uh cells. It actually gets inside nerve |
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| 17:45 | , cells of the central nervous, nerves and then nerves to the central |
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| 17:49 | system. So nerve cells is it's your host. OK. Um And |
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| 17:55 | the only cell types it will OK. So that's what we mean |
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| 18:00 | tissue specificity and that can be brought broad on error as well. And |
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| 18:04 | your HIV again, in fact, very specific type of cell of the |
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| 18:08 | system called the T helper cell. , and it's actually a very specific |
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| 18:13 | of to help cells because we have types of those. So uh cold |
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| 18:18 | only affects cells of the uh mucus of their respiratory tract. Um Ebo |
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| 18:25 | respiratory tract, Ebola is very it can affect cells, uh potato |
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| 18:30 | , endothelial cells which make up blood . So it's a very uh um |
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| 18:35 | range, OK. It actually the that is like that explains why it's |
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| 18:41 | very deadly. Ok. Because it um uh infect a number of different |
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| 18:45 | types, causing inflammation, uh loss fluids, et cetera. It's a |
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| 18:50 | nasty disease. And in large part of the different cell types in the |
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| 18:55 | that it can infect. Um So viral gm, so viral |
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| 19:03 | um of course, can because viruses span a range of size from about |
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| 19:09 | nanometers to nearly 1000. Then of , that means they can accommodate a |
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| 19:14 | or larger genome. Uh which means have more genes than that genome. |
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| 19:19 | so the genes that viruses code Again, even though viruses um rely |
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| 19:24 | the host for a number of different . There, of course will be |
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| 19:27 | genes and uh in the genome that for virus specific components, right, |
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| 19:33 | will be things like capsid proteins, Other associated proteins that are in that |
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| 19:39 | envelope and or captured. Um and can be that are critical to its |
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| 19:45 | cycle. Uh some synthesize its own of their own. A and from |
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| 19:51 | , for example. So these are kind of things we're talking about |
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| 19:55 | Um This is a couple of here is the genome of the Zika |
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| 20:00 | . Um It is an enveloped virus you see there, it has specific |
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| 20:06 | uh that are of course make up capture and those that make up uh |
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| 20:10 | proteins. The E and mm protein you don't need to know these |
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| 20:14 | But just kind of an example of different types of proteins, virus specific |
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| 20:18 | proteins that are present and, and will be included for by their |
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| 20:22 | OK. And so Zika virus uh a AAA single strand RN a |
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| 20:29 | it's called plus strand. Um It's single molecule which that's what non segmented |
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| 20:35 | to uh about 11,000 nucleotides in uh which means approximately about 10 to |
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| 20:41 | genes. Uh And here are some of these are virus specific proteins that |
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| 20:46 | be um that it will encode for , coding for these various proteins of |
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| 20:52 | in an envelope. So um the , all right. So that too |
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| 21:01 | a uh envelope virus. You could like a protein spikes. Um the |
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| 21:08 | genome in the uh within the capsid kind of the pink coiled structure, |
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| 21:14 | number of glyco proteins. Uh So has that typical um envelope structure of |
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| 21:21 | virus. It two is a plus strand of a virus and this genome |
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| 21:26 | also within the size range of A Zika virus 10 to 12,000 |
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| 21:32 | Um The influenza virus is the minus a strand genome. And it's |
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| 21:38 | it's an example of one where the is segmented. So you see eight |
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| 21:42 | segments that mix up this genome, size range as uh Coronavirus and Zika |
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| 21:50 | . Uh 13,000 base, uh nucleotide and proteins encoded and again, had |
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| 21:55 | number of different um um virus specific . It uh possesses now one thing |
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| 22:04 | about the flu virus is because of segmented genome. Uh it can recombine |
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| 22:13 | it can infect. So the other to remember is that when viruses infect |
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| 22:17 | certainly more than one virus can infect single cell. And as those viruses |
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| 22:23 | , it's possible that genome recombination can within the host cell. That's exactly |
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| 22:27 | happens with the flu virus. flu virus has its origins in um |
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| 22:33 | , uh aquatic birds, things like , geese, et cetera. And |
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| 22:38 | from there, it passed on through fowl, like chickens and things as |
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| 22:44 | as ducks and then actually in the as well um and eventually into |
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| 22:51 | So the variants you see there, ducks, the H seven N three |
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| 22:57 | in wild burns, age seven and , domestic poetry, age nine and |
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| 23:01 | . And the ancient N numbers referred these particular viral proteins. The |
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| 23:09 | that's the end and the hemoglobin is H. So that's what the H |
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| 23:15 | N refers to. And the, actually both play a role in the |
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| 23:18 | life cycle. The hemo glutton is involved in attachment to the host cell |
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| 23:24 | facilitates entry and the neuro actually facilitate exit of the virus from the host |
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| 23:29 | . So they both have uh opposite but uh their importance as well is |
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| 23:35 | when, when there's changes in these , then that can change the effectivity |
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| 23:40 | the virus. Um And so we trace kind of the genome origins or |
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| 23:47 | viral or two viral origins through this and where it has acquired these from |
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| 23:53 | various previous animal hosts. And reassortment can occur uh with these viruses |
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| 24:01 | uh similar, same cells. And you see there uh so these are |
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| 24:07 | coded. So, from the domestic , the H seven N three is |
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| 24:10 | blue coat blue. Uh the wild , H seven N nine virus in |
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| 24:16 | and the domestic poultry H nine and in red. And so you see |
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| 24:20 | they've recombined um these forms in what's, what is the H seven |
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| 24:25 | nine virus uh from 2013 which then uh infective uh in, in humans |
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| 24:33 | well. And so, of for, for this to, for |
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| 24:38 | , for a form to recombine and infectious in humans, of course, |
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| 24:41 | must be contact with humans with these because that, that's the only way |
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| 24:45 | the virus can, can evolve into form that's infectious in humans by having |
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| 24:50 | and getting into the humans. And that it can occur in different |
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| 24:54 | Um uh but that is a central of it and that's, you |
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| 24:57 | flu virus changes, obviously, as know from season to season. Uh |
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| 25:02 | , the flu vaccine changes from season season for that reason because it um |
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| 25:07 | the virus changes and evolves as well these kind of reassortment and mutation |
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| 25:13 | Ok. Now, um and that's common for all viruses is to |
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| 25:18 | Um They don't, um their replication on the host and, and there's |
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| 25:25 | , we, we have repair mechanisms fix mistakes when we copy our |
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| 25:29 | But viruses don't, don't. And they can generate mistakes in their, |
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| 25:35 | their genome replication uh at a much rate. And um that's what can |
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| 25:42 | , you know, them to change much more rapidly than, than, |
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| 25:46 | other types of cells. No. So here just kind of a bit |
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| 25:52 | a just to summarize the virus structure just went through. OK. So |
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| 25:56 | begin with the definition, right? definition a cell requires a host, |
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| 26:01 | lacks a metabolism uh structure, So the caps, right? So |
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| 26:04 | basic virus structure that all viruses have a CAPD surrounding a um genome, |
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| 26:12 | ? So it could be uh he sided geometric shape or it can be |
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| 26:18 | filamentous helical form. OK. GM DNA RN, a single stranded, |
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| 26:24 | stranded, it can have an envelope not have an envelope, right? |
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| 26:29 | or envelope virus. Uh And that's acquired from the host, it |
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| 26:34 | um other things, maybe we have protein spikes sticking out of it. |
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| 26:38 | or no. Uh certainly it will virus specific specific proteins for sure. |
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| 26:43 | . So again, that caps if it's a naked virus that caps |
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| 26:46 | will have captured proteins, there may other proteins in there as well. |
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| 26:49 | similar with the envelope virus, there be envelope proteins and of different |
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| 26:55 | right? And some of these will involved in in recognition and attachment to |
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| 27:00 | host. Ok. So again, mentioned, the the viral life cycle |
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| 27:12 | in large part is turned by the it has. And so the genome |
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| 27:17 | A and so you think of it terms of what can that genome be |
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| 27:21 | for in terms of when it's OK. So the genome of a |
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| 27:25 | virus can serve as a template for , right? Just like ours, |
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| 27:29 | ? Our DNA can, can be into RN A and and of |
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| 27:33 | it can be copied into DNA as , as we undergo DNA application. |
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| 27:38 | similarly for viral uh the DNA it's the same thing. OK. |
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| 27:44 | again, it's using pretty much it's using hosts uh resources to do |
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| 27:48 | . A viruses. This is where a little bit more variation. |
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| 27:52 | So your plus RN A viruses, remember what the plus and minus, |
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| 27:57 | sense, anti sense uh plus is uh minus is template. OK. |
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| 28:05 | a A plus RN A virus uh template can be translated. OK. |
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| 28:12 | is combined to it and synthesized OK. So the plus A plus |
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| 28:20 | , OK. Equals a messenger RN . OK. Now, they might |
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| 28:32 | saw a new virus that genome serves a template to make an MRN |
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| 28:38 | right. So again, a minus , a virus will copy it genome |
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| 28:44 | produce a, to produce an a transcript that can then be |
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| 28:49 | OK. The minus RN A genome be directly translated. It must first |
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| 28:53 | copied into a transcript. Then we uh a complete, complete oddball or |
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| 29:00 | , right? So these, it's genome is a template to produce |
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| 29:06 | , not RN A. OK. so it does. So um we'll |
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| 29:11 | more about that next time. But it's DNA template is actually concrete to |
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| 29:19 | , are they? And I'm you back that up. It's RN |
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| 29:27 | template, it's RN A genome. . RN A genome is copied |
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| 29:42 | oh excuse me, it copied to a DNA which when it wants to |
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| 29:51 | a replication cycle, it will copy DNA into RN A and then translate |
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| 29:58 | protein. OK. So they go to the um to the um central |
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| 30:08 | , right? Where information flows the RN A, the protein retroviruses |
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| 30:14 | a variation of that. They're countered that. So they have RN A |
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| 30:17 | that can gets copied into DNA and to RN A and then the |
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| 30:21 | So uh remember that that's an important concept. OK. So they're countered |
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| 30:28 | what, how information flows in every living thing, not that viruses are |
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| 30:32 | living things. But when they're you can consider, consider them to |
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| 30:36 | living. Uh But uh and they a particular enzyme that allows them to |
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| 30:41 | this, we'll talk about that in next, in the part two |
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| 30:45 | Um So in classification, so you , you can think about, you |
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| 30:52 | , the differences among viruses. You , the differences in genome DNA |
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| 30:56 | a single stranded, double stranded. it have an envelope? Does it |
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| 30:59 | have an envelope? Um uh The shape is it polyhedral? Is |
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| 31:04 | is it uh filamentous or helical? it, is it complex? |
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| 31:08 | So they're all me all criteria you use to classify a virus. |
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| 31:12 | Um So in this um scheme you see um this classification is based |
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| 31:20 | the genome type and the presence or of an envelope. OK. So |
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| 31:24 | see that there are six classes identified on that criteria, right? So |
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| 31:29 | groups one through six groups, one two being in DNA. Um viruses |
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| 31:37 | by uh double stranded, single stranded , absence of an envelope. The |
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| 31:44 | A groups of course come in uh varieties. You have the single |
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| 31:48 | double stranded uh and single stranded, um plus and minus, single |
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| 31:56 | And then the sixth group is the which uh use the template for deo |
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| 32:01 | and don't memorize this table. Uh only highlighted circle there uh A |
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| 32:07 | the four and five group, the ST AIA viruses, the plus and |
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| 32:13 | minus. This is the plus group . This is the minus group |
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| 32:25 | These books contain a number of viruses you're familiar with. Your measles and |
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| 32:29 | , your cold virus rabies. Uh fits in here. Um uh So |
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| 32:37 | West Nile virus which is, which uh endemic in this part of the |
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| 32:42 | . Um A number of different ones familiar with are in are in these |
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| 32:46 | groups, the plus and minus single of RN A viruses. Um |
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| 32:55 | so let's talk a little bit So we went over this previously just |
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| 32:59 | kind of set up the uh uh gonna finish here with the bac uh |
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| 33:05 | virus life cycles, but then we'll in part two with animal virus life |
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| 33:10 | . So, just uh remembering um steps here, right? So, |
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| 33:15 | recognition and attachment, of course, crucial and there's gonna be variations at |
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| 33:18 | of these steps, there's variations depending the viral type. So, of |
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| 33:22 | , is of recognition uh and binding the host cell occurs. Um |
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| 33:27 | obviously, envelope proteins uh of different can be of importance uh in this |
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| 33:35 | as well as you know, some , certain viruses present, uh proteins |
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| 33:39 | in this capsule will be instrumental in process. So, again, specific |
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| 33:44 | on the surface of both the virus host are what bring this about um |
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| 33:49 | . So as mentioned, the the captures may come in which is common |
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| 33:52 | animal viruses or not bacterial viruses don't it that way. Only the genome |
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| 33:58 | Once we have it, then basically and assembly and synthesis of our |
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| 34:03 | assemble our particles uh exit and then the host and then go on to |
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| 34:09 | other cells. And again, the of the host can vary. |
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| 34:15 | The um material phase life cycles which will focus on first and end this |
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| 34:21 | section. Um uh it can be tree type. So what we call |
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| 34:27 | cycle. So you're what are called P pages as you see there, |
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| 34:31 | are what these are the complex viruses have the captured, then they have |
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| 34:35 | uh the sheath part you see which is this, which is this |
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| 34:41 | right here. OK. That's the . Um And then the tail fibers |
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| 34:51 | see there. So certainly the tail are part of the recognition mechanism and |
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| 35:03 | the uh sheath is actually acts like spring uh pressurized spring that, that |
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| 35:09 | the genome into the uh host OK. So again, all the |
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| 35:16 | parts of that virus are staying outside cell, only the genome is |
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| 35:19 | And that's common for bacterial viruses. so light phage are types that basically |
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| 35:27 | infect the cell, infect the produce lots of viral particles and overwhelm |
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| 35:33 | cell and kill it. OK. is gonna lice the cell eventually but |
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| 35:37 | of P particles are gonna exit that lysogenic phage. And and then I |
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| 35:43 | mention another term for lytic P is , virulent PPH light P typically refer |
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| 35:50 | the same thing lysogenic pha will be temperate. So they can um kind |
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| 35:56 | remain dormant in the cell, not affecting it, but then can uh |
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| 36:04 | a a lighting cycle at some point order to replicate itself and then kill |
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| 36:09 | cell as it exits. So Lyo cycle is one that does not kill |
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| 36:14 | host immediately, right? It forms intermediate state called the prophage, |
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| 36:19 | So that's where the bacterial genome will into the host genome. And during |
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| 36:25 | phase, the host cells completely viable unaffected and and can grow as it |
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| 36:32 | would. But at some point uh stresses or other cues will initiate the |
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| 36:40 | of the virus entering a light cycle . And so we'll see that |
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| 36:45 | So it can reactivate to become light it comes out of the genome of |
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| 36:48 | host and then assumes its viral form uh replicates. OK. And |
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| 36:54 | it's all about what's what's going on the environment. What's the state of |
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| 36:57 | host cell kind of dictates this. first look at the la cycle and |
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| 37:02 | can break this down into five First is attachment. So uh recognition |
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| 37:09 | the page to the host cell um is where the brown genome enters. |
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| 37:16 | that everything else stays outside the cell enters. Uh it will direct um |
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| 37:22 | of certain in what are called early uh proteins in it for the life |
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| 37:27 | . Among these are ones that will the DNA. So you see the |
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| 37:31 | fragmented, the host DNA fragmenting. you can then use those nucleotides to |
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| 37:36 | its own DNA. Um then in , uh so we have attachment penetration |
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| 37:44 | is where of course uh translation of proteins is occurring. OK. Uh |
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| 37:51 | DNA is being copied and uh proteins being produced. Maturation is where we're |
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| 38:00 | , assembling viral particles. Uh in essence of our particles are mature |
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| 38:07 | infectious uh particles. So, during time, it's what we call the |
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| 38:14 | eclipse period. That's the period from uh the genome enters and begins to |
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| 38:20 | synthesis of viral uh uh components and assemble them together. OK. Um |
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| 38:30 | , and there's the assembly process how occurs. Um then release occurs. |
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| 38:38 | so um the eclipse period occurs up the point until there's intact viral particles |
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| 38:44 | . OK. So the eclipse period the kind of the steps prior to |
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| 38:49 | complete formation of viral particles. Uh Once that maturation has occurred, |
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| 38:56 | of course, there can be 100 up to 500 phage particles per |
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| 39:05 | And uh the virus also has a synthesizes lysosome lysozyme excuse me, lysozyme |
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| 39:12 | down cell walls. And so the of the very high amount of pha |
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| 39:20 | and the seis of lyo lysozyme, me will burst the cell. And |
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| 39:26 | you have many, many, many , exiting and going on to infect |
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| 39:30 | host cells. So that's, that's lighting cycle. So it um and |
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| 39:38 | can occur relatively rapidly. Um The you can imagine that when you have |
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| 39:45 | exit of 2 to 500 per and the bacterial culture can have, |
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| 39:50 | know, millions of cells uh that as as the release of phage occurs |
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| 39:58 | very quickly, uh the cells in population will be obliterated and uh um |
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| 40:06 | quickly. Um He so uh these fate can be quite um quite uh |
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| 40:15 | quite well. Now, the lysogenic , as mentioned, our example here |
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| 40:21 | lambda age. It's called lambda age a type of bacterial virus that can |
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| 40:25 | integrate its chromosome into the host And so, of course, it |
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| 40:32 | with the same process of attachment, , and then penetration. So where |
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| 40:36 | uh virus attaches, recognizes and attaches host, then uh the genome enters |
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| 40:45 | uh cell cytoplasm. And it's at point where it can integrate into the |
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| 40:52 | chromosome. OK. So you see integration of that uh pha DNA into |
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| 40:58 | chromosome from your prophage. Um and , the host cell again is not |
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| 41:07 | affected. It can, it grows the eyes as it normally would. |
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| 41:10 | so you see there knowing how fast can divide very quickly, you can |
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| 41:14 | a lot of cells, each one a copy of that prophage. |
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| 41:19 | So now the prophage actually will proliferate the entire population as the cell |
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| 41:27 | But at some point, there's gonna environmental cues that will say that will |
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| 41:33 | the virus um to, to exit um lygen state because you have to |
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| 41:40 | that is uh although we can perpetuate by the cell dividing and the chromosome |
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| 41:50 | the host cell in a copy of prophage, ultimately, you will have |
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| 41:55 | get out of that state and into lighting state in order to uh direct |
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| 42:01 | that genome to produce new viral Ok. So eventually that will happen |
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| 42:06 | uh that's the only way for the to replicate and produce new viral particles |
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| 42:10 | to do that. And um if are environmental conditions are such that uh |
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| 42:16 | the, the survival of the virus is in danger, then it's going |
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| 42:21 | come out of that Lygen state into life cycle. So it can replicate |
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| 42:26 | then go on to infect more Um And that's essentially what it does |
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| 42:30 | time. So cells that um so we say it cells Vigen, that |
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| 42:35 | it contains a prophage, that the genome is integrated into the host chromosome |
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| 42:40 | those that are there in that state immune to infection. So, uh |
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| 42:45 | example, this cell here containing a will not be susceptible to an infection |
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| 42:51 | another lambda virus. The the the itself expresses certain proteins that prevent that |
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| 42:58 | happening. Um The uh but also with the, with the, when |
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| 43:08 | , when the um phage genome exits chromosome here, right? So say |
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| 43:14 | go back to this state. Or let's just go, excuse |
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| 43:20 | let's go to here. So we from here to here and you see |
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| 43:24 | genome exits, there's times when that can exit and actually take part of |
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| 43:29 | host, some of the host DNA it. And, and then that |
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| 43:32 | packaged, that's a form of And we talked about earlier. Uh |
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| 43:36 | actually, that's actually the example of specialized transduction that that can occur with |
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| 43:41 | uh lysogenic age, the back up . So the lytic pha, |
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| 43:46 | they're the type that can carry out generalized transduction. So note that here |
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| 43:51 | it breaks up the DNA of the chromosome, that parts of these particles |
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| 43:57 | be packaged into the page instead of instead of the host of instead of |
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| 44:02 | viral genome. And that's where we generalized transduction, right. So generalized |
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| 44:06 | is generally a product of can be part of the light cycle from light |
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| 44:12 | and the lysogenic pha or what contribute the specialized transduction. So in that |
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| 44:19 | , transduction involves the viral intermediate that's the genes on from one bacteria to |
|
| 44:24 | . Ok. So, um yeah, and with lysogenic phage, |
|
| 44:30 | , it's like uh this dormant this prophage state uh leaves the hotel |
|
| 44:37 | healthy and able to replicate. But , it must um come out of |
|
| 44:43 | state into the lighting cycle in order form viral particles. And so it'll |
|
| 44:48 | this genome to do that. Um , uh and we'll see a variation |
|
| 44:54 | this with animal viruses because there are viruses that can also integrate their uh |
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| 44:59 | into the host. And so, we just don't refer to that as |
|
| 45:03 | . OK. Um We just call a provirus state in, in animal |
|
| 45:09 | . So, um uh one last to say so with your bacterial |
|
| 45:13 | they're, they're pretty much to my , only DNA viruses. So, |
|
| 45:17 | viruses or DNA viruses. Um And this is a couple of examples of |
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| 45:24 | light cycle and lysogenic cycle. The so, uh so that concludes the |
|
| 45:31 | one. So again, this is red, the structure, uh |
|
| 45:34 | the structure, uh classification and then little bit about um life cycles specifically |
|
| 45:41 | to the bacterial viruses. OK. on part two, we'll go into |
|
| 45:47 | just talk Exclu exclusively on um animal and how, how they vary among |
|
| 45:54 | and from bacterial viruses in terms of bio. All right. Thanks, |
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| 5999:59 | |
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