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BIOL 2321_Microbiology for Science Majors - 3332_CH 06 Part 1 Video Lecture
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00:01 Welcome in this module. We're gonna viruses, viruses and prions. In
00:06 first section we're going to look at viral structure definition of a virus viral
00:13 relates to its infectivity and a little about classification of viruses. Um The
00:19 module on part two we look at life cycles, both bacterial and various
00:25 virus types. Um So it's a bit of get started here. The
00:32 course viruses weren't discovered for quite some after bacteria war discovered. Many do
00:38 course is a very small size of . It requires really electron microscope to
00:45 these. But they're um the discovery was found by looking at this virus
00:55 causes disease and tobacco plants and uh disease and healthy tobacco plants by
01:03 And I've Janowski um use the technique filtration, thinking that they were dealing
01:10 a bacterial agent of disease. Um would have been a common thing to
01:19 because of course this is during the when following cokes postulates and discovery of
01:25 bacteria are the cause of diseases of diseases that naturally they had the kind
01:30 the same same thought process. So it would take the diseased plants crush
01:37 the leaves and uh filter the thinking that bacteria would be trapped on
01:48 of the filter and then they'd have agent of disease. But it turns
01:53 that when they tested the material on filters thinking they've trapped bacteria uh and
02:02 administered that the healthy plants, it never cause disease. It was only
02:05 they took to fill trait, the that went through the filter obviously being
02:10 tiny uh organisms. Then uh then fill trade itself is what actually would
02:17 disease when they applied it to healthy . So they knew they were doing
02:21 very very small. Much more so bacterial size. It wasn't until later
02:28 that development electron microscope that they were to visualize uh these uh Viruses and
02:36 turned out really to be on the end of the spectrum in terms of
02:39 size 20 nm. But about about nanom size range is very very
02:47 Of course. And so so of now we know what versus structurally are
02:52 about. And there's a whole they a range of sizes. Um So
02:57 course, you know viruses require a to replicate the kind of occupy that
03:04 in life. Where are they living not living? Um Of course when
03:10 are in a host and replicating you could consider them alive. Um
03:16 in fact all all taxonomic groups. there's viruses that are specific to almost
03:23 every life form on earth And even and affect other viruses. Um so
03:30 a result they basically found everywhere as . So like bacteria we call them
03:34 viruses right? Um but also we really in the last 10 years or
03:41 the the benefits of viruses. So do have an ecological importance. And
03:49 here just shows the kind of the range on the larger size and nearing
03:57 one micron is the Ebola virus on smaller end are things like the tobacco
04:03 virus. Um through pages. Um you know, roughly 20 nanometers as
04:12 as 20 nanometers up to as large almost micron. But there are
04:15 we'll talk about briefly, I would it giant viruses which are which are
04:20 micron and larger. So uh so spend quite the size range now the
04:30 they do have important roles in They can of course, in fact
04:37 organisms. And in doing so by them, they convert into organic materials
04:45 can be used by others in the . And so it's what's called the
04:50 shunt that um this organic material of provides provides nutrients for for um different
05:01 of organisms above, above that in in the ecosystem. And so as
05:10 , they can have effects like on controlling populations of those that cause uh
05:17 these toxic uh allergy that uh that that can blow up in population size
05:27 marine environments. Uh when they proliferate of these produce toxins that actually can
05:33 fish. And so there's viral types can actually keep a check on those
05:38 as well. So, so viruses have an important role in ecologically from
05:44 aspect. Um so when we talk defining a virus, of course we've
05:51 before that these are a sailor They don't have the properties of
05:57 They can't replicate on their own. course, they don't have really have
06:00 metabolism. They don't carry out protein uh within within their on their
06:09 So they rely on the host for of their functions. Okay. And
06:14 most basic all viruses are comprised of genome. DNA or RNA surrounded by
06:22 protein coat or caps. It all will have that basic structure.
06:28 of course there'll be variations and will on that basic definition or that basic
06:35 . But all viruses do have that common a genome of course, and
06:40 a protein coat or caps it around it. Um captured proteins. Uh
06:47 capsule shell is comprised of units called mirrors. And so as mentioned in
06:58 for them to proliferate, they must the host and basically used to host
07:04 to make more viral particles. But all begins with and we're just gonna
07:10 through kind of a basic viral It all begins with the virus being
07:14 to recognize the host. If that happen, then the virus is not
07:17 to replicate. And so there's gonna a specificity there of the virus for
07:23 particular host cell type. This all with molecules that are on the periphery
07:29 the virus and the host. So obviously occurring at the interface of the
07:35 cell membrane and the viral uh surface the molecules interacting between the two um
07:44 the host of course things like DNA , RNA polymerase, ribosomes, RNA
07:50 um are required. And of course primary unemployment rates that will vary uh
07:59 on the genome that the virus Whether it needs these components. Again
08:08 lack a metabolism. So you know relying on the host for for for
08:15 processes and as a result obviously it a toll on the host in terms
08:21 energetic six uh and and supporting this replication that's going on. And so
08:29 the host suffers to some degree. Of course depending on how active the
08:36 is within the cell. Um So is if recognition of the virus of
08:42 host is successful, then the viral is enters and then that will begin
08:46 make copies of the genome and in cases the the genome may integrate into
08:53 host chromosome. There are viral types do that. HIV does that,
09:00 herpes simplex virus does that. Um there papilloma virus does that there's other
09:06 that their life cycle is to integrate the host chromosome. Um So one
09:12 to keep in mind is that um virus that enters its host, it's
09:20 to of course I want to make to make lots of viral particles.
09:24 that means lots of materials gonna be from the host. Okay and so
09:30 copies of genomes because each viral particle going to be produced, we will
09:34 to have a genome in it. obviously copying the genome is important.
09:40 the complex forms inside this host called replication complex which is basically a factory
09:48 make the viral particles. So of there's transcription translation of the viral
09:56 expect to express the viral genes into viral proteins which then are assembled into
10:03 ins um and uh variants are the . And then of course once they
10:13 formed they will exit the host and go on to infect other neighboring
10:21 Basic life cycle of any virus. of course we're gonna as we go
10:26 and look at different viral life So there will be some variations here
10:31 there but overall it kind of follows process. Okay, it has a
10:36 influence is the nature of the viral RNA or DNA. And that can
10:42 you know where where events occur in cases so within the cell, I
10:49 um remember that animal viruses in fact and some in some cases viruses go
10:56 the nucleus as part of the life . And other times they don't often
11:01 on the nature of the viral genome viruses of course don't. There is
11:06 nucleus in the bacterium. So basically of the viral cycle occurs within the
11:14 of that um bacterium. So Um so as we look at infectivity
11:21 course is very important. Uh and can have a range of hosts.
11:29 uh what's called Either narrow or broad can affect a number of different hosts
11:35 it's relatively narrow. Examples are things rabies virus of course can affect many
11:41 types of hosts, malian hosts of humans, dogs, cats,
11:48 various rodents etcetera. Okay. But of course our narrow range HIV infects
11:54 humans for example. So it can . Um Then of course there's the
12:01 to affect multiple hosts. Okay. but then with within a single
12:08 how many different tissues can be So how many cell types within a
12:15 host can be infected? That's what refer to as trope is. Um
12:19 so think of it as tissue Um And so there again it can
12:25 brought on narrow and so Ebola of can affect multiple cell types in a
12:32 host. That's one of the reasons it can be so deadly. Um
12:36 can infect cells making up blood vessels are called cells and they can infect
12:45 uh other types, other cell types the body as well. Um The
12:52 range or something like a cold virus in fact you know only sells the
12:57 lower respiratory tract. Um HIV infects specific cell type type of so called
13:04 immune system cells called the t. cells. So very narrow range.
13:09 so again whether it's broad or narrow all about the types of molecules the
13:16 recognizes. Okay, so here's a target cell. Here's a viral
13:21 Whether that virus will be able to is all about interaction with specific molecules
13:29 the host. And uh it may able to interact with michael types shared
13:36 various cell types in the body, it a broader range or marriage is
13:40 specific. Like HIV only recognizes a type of receptor on a immune system
13:47 cell. And so that's that's that's dictates the infectivity and infectivity relates to
13:57 being to recognize a host get inside begin to replicate. Um No in
14:05 of viral structure. So we can first look at what it called metrical
14:11 . Uh these will have a Geometric of pattern shape to it. So
14:17 casa hydra was 20 sided. As see there. So they can have
14:22 um cemeteries, accesses, cemeteries, twofold, threefold and fivefold. Um
14:32 are but there's a simplicity to the . So we have to remember that
14:36 don't have large genomes and they have economize in terms of the number of
14:45 and what they express. And so captions They may produce maybe 3-4 or
14:51 different types of captured proteins. But they combine in combinations to produce the
14:57 . So as you see here the a virus has four um capital types
15:04 proteins that they assemble into these into cost federal shape. Okay, so
15:13 aside from that basic capital structure that the genome, there can be then
15:18 viruses and naked viruses and naked viruses will lack an envelope. An envelope
15:24 has an additional layer surrounding the Okay, as you see there,
15:28 herpes virus is an enveloped virus. you see the hexagon captured in the
15:34 uh surrounded by that large envelope. then of course various uh envelope proteins
15:41 are embedded into that uh envelope. so of course those envelope protein is
15:48 to be instrumental in in for the to infect. That's what that's what
15:53 envelope proteins are gonna what what will particular host surface molecules and that will
16:00 if recognized and they and they match then you'll have infectivity occurring naked viruses
16:07 envelopes. They too will have obviously proteins are gonna have other proteins on
16:12 surface as well. Uh So for proteins, we often see these carbohydrate
16:21 molecules called glycoprotein spikes, spikes because very prominent and they stick out as
16:27 see there again involved in host recognition and or attachment of course uh and
16:35 other types of functions as well. . Um and there is an
16:42 So dinner viruses, a non enveloped , a naked virus but it too
16:47 glycoprotein spikes. Okay. Um and just for you know, we're all
16:56 coronavirus these days. So this is that looks like. It's actually an
17:02 virus and there's actually many RNA viruses we're familiar with. Measles,
17:08 Ebola, uh West Nile virus. cold virus flu virus. A lot
17:15 the viruses were familiar with phone to RNA category. Uh And again you
17:20 this is an enveloped virus. You the glycoprotein spikes are very prominent.
17:26 . Um so just an example, example of an enveloped virus uh not
17:33 viruses are also symmetrical. They will a more elongated structure to them.
17:42 kind of like a tube like Uh Again from price of captured it's
17:49 and uh a genome uh of course wrapped inside it. Uh Ebola is
17:57 type of filament this virus um M bacterial type of filament this virus.
18:03 you can also have those that are tailed viruses. This is a type
18:08 sea among many different bacterial type viruses bacterial fage is we call them um
18:15 T4 bacteriophage ages the type that has structure, you do see the capsule
18:22 . They contain the genome but then see these additional structures and these are
18:26 for the tail fibers of course are buying recognition and binding to a host
18:33 the actual tube or the sheath they it actually kind of a tube that
18:41 compress. And and it's through which genome will pass and enter into the
18:48 . So you can have some kind more um um bury instructors from your
18:57 types like the filament this and symmetrical filament is and the cost of federal
19:04 . So um asymmetrical viruses influences example that lack captured cemetery. So they
19:11 have this geometric shape that can be kind of um although it was kind
19:18 pretty much a circle there, they to be more oblong and oval
19:24 not perfectly round. And so hence call them asymmetrical. Um uh and
19:30 flu happens to also be an envelope as well as you see there.
19:33 the green the green is the camps surrounded by a an envelope.
19:40 Um Alright so thyroids now so we're take a little bit of a detour
19:47 for a couple of slides. So this point we've been describing the structure
19:53 viruses. Okay so Vai roids and are not viruses, viruses have their
20:00 structure of Eiroy AIDS are variation there RNA molecules. That's all they
20:07 There's no there's no captured uh it's just an RNA molecule. Okay.
20:14 but there's types of these plants, virus that we are aware of.
20:21 as far as I know only exclusively types that are known only exclusively infect
20:28 . Um There are no human pathogens thyroids. The probably the most famous
20:35 I guess is this one that causes and potato plants called potato spindle
20:40 Bayreuth. So regardless the the RNA uh of course replicated by the host
20:48 polymerase to make more copies. Um army is not does not code for
20:53 . Okay, what it does it are some that can have catalytic
20:59 So there are RNA molecules in general can have catalytic capabilities. The one
21:07 part aware of is the the are a in in Arriba zone that capitalizes
21:14 bond formation for example. Um But the thyroid it interacts, it's
21:21 N. A. Interacts with transcripts the plant to alter expression of genes
21:28 the plant and that's how it causes . Um So bottom line with
21:34 they're they're an infectious RNA molecule that replicate using host polarize. Um and
21:41 can interfere with gene expression in the . Um Pry un's again, prions
21:50 viruses but they are infectious proteins. , so again the virus is an
21:57 molecule, the prion protein. And so the there's no nuclear acid
22:04 is simply just a protein. And prion disease we're familiar with is what's
22:13 spongiform encephalopathy, you know, as cow disease. Um And the general
22:21 . Uh It can be found of in different types of livestock cattle,
22:27 . Uh It was first found in actually um of course humans uh and
22:37 causes a disease that affects of course uh brain cells and uh causing a
22:51 neurological condition. And so in it's called creutzfeldt Jacob disease or
22:57 kuru, um sheep, it's called regardless. Um the diseases transmitted through
23:09 food barn and I'm sort of So as mentioned, the prime diseases
23:19 transmitted through food from infected animals the virus is in the food supply
23:29 then it can be ingested by someone are these prions are relatively resistant um
23:38 normal types of disinfection treatments and So it can be a they that's
23:45 they can pass through food and uh cause disease. Now here in the
23:49 it's rich, it's next to nothing rare. Uh we have pretty good
23:57 of types of foods that come into country and Uh so it's really not
24:03 issue for us, there was maybe years ago um outbreaks here and there
24:09 England. Um but again, it's been an issue for us here in
24:16 States, but regardless uh think about is it's a protein that's infectious.
24:21 so how does it perpetuate itself? it does so by uh combining with
24:31 normal form of the protein. And apparently is what induces to assume this
24:39 shape and that's the infectious form. it's a it naturally occurs in
24:48 this protein, the normal form of protein and uh it's still unknown really
24:54 the exact function of it is. we do know that when it's
25:01 not working properly, it can cause . And so how it perpetuates itself
25:09 through, as I mentioned, the of a prion protein to a normal
25:14 . And this approach it kind of a chain reaction and these can
25:20 So these uh misfolded forms kind of together in like a kind of like
25:28 polymer if you will. A prion and these serve to of course affect
25:35 cell function. And so the these create than killed neurons, neurons and
25:46 basically holds in the tissue and as accumulates over time it's a very slow
25:53 disease. But as it progresses over um do the plaques as they're often
26:02 that form in the brain tissue. changes the consistency and texture of the
26:06 . Such it becomes kind of more like and obviously that's that that result
26:11 severe neurological um symptoms and conditions. um obviously this is ultimately gonna be
26:23 . The as mentioned, they're very to physical chemical agents. Um So
26:31 we look at here's an example of neuron uh that would make the normal
26:43 that you see there in green um version of the protein. And again
26:49 private version of the protein could be be presumably through and acquired through ingestion
26:55 food. There is evidence to that maybe a genetic component to this as
27:00 . Um But regardless the the misfolded combines with the normal form and induces
27:07 change in shape. And so you the accumulation of red of the red
27:11 proteins that aggregate and um and then destroy the cell creating plaques for the
27:19 has died. And so these accumulate time again and neurological conditions result from
27:27 . Okay, so um so it's it's a it's a type of
27:33 that um infectious protein that causes a . Okay. Beyond this particular um
27:43 type of disease. I'm not aware any other kind of prion related diseases
27:47 this. Okay. Um but so to summarize so vai roids and prions
27:55 not viruses completely different structure ones and RNA virus roids ones and infectious protein
28:04 . Okay, so getting back to then we look at viral genomes obviously
28:11 viruses are relatively small and they're going have a small genome. Of course
28:17 a size range of viruses and large can of course accommodate larger genomes.
28:22 on the upper end is I think polio virus is on the upper end
28:26 may have upwards of close to 100 or more. Um Others on the
28:32 end of the range may have 7-8-10 . And then of course spanning the
28:40 in between Zika virus. You see an example of a of a what's
28:46 a non segmented. Right? It's single piece of the fake acid in
28:51 case a single stranded plus RNA And um and it was just an
28:58 of this is this is probably about average size for a virus. About
29:04 nucleotides and size uh carrying a few . You see there some of these
29:13 are for um the proteins uh and functions. The influenza virus is unique
29:23 that it contains, it's what's called segmented virus. So it has multiple
29:27 genome segments in this case they're single uh minus RNA genomes, Eight segments
29:34 those that are organized into the capsule um and this one code similar in
29:43 to the Zika virus, a little little bit larger quoting for 11 proteins
29:49 . And uh with the influenza this has been its origins are an
29:56 aquatic birds. So ducks and things like that, which then over
30:03 spread into domesticated fowl chickens, for , domestic ducks and then um and
30:12 well as swine pigs and the virus institute for Essentially true for any of
30:19 viruses when they in fact there can more than one Type of impact and
30:24 can recombine their genomes, which is influenza virus can do. And so
30:32 the numbers H&N. You see the virus, H2 into these refer to
30:39 proteins that are on the surface of virus. One of these is involved
30:44 attachment and actually elements actually involved in exit of the virus from the
30:50 And so both are required but changes these ancient and proteins in the virus
30:56 come about through mutation and and re of viral types in these animal hosts
31:06 of course in humans. So you a reassortment and uh rearrangement of these
31:11 genomes. Such you have uh genomes segments from uh different hosts that can
31:18 combined together uh and in some of combinations forming uh variants that are infectious
31:27 humans. The H three N two example. Um So um so that
31:35 flu flu bars is unique in having uh multiple segments as part of its
31:42 . Now as mentioned there are these viruses and so mm virus is is
31:53 of these pitta virus virus are these large types of viruses uh infecting things
32:00 amoeba. So uh these are of infecting you carry out type cells.
32:10 so as a result of being very larger genome of course uh may have
32:17 some some metabolisms okay, not extensive eukaryotic cell or bacterial cell would but
32:26 know, remnants of some of some as you see their metabolism, lipid
32:34 . And so uh some of these , large viruses that is even half
32:40 that viruses that infect them. So see there in the lower right is
32:45 memo virus, the large particles and within one of those you see smaller
32:50 which are actually uh what are called fage there are viruses that infect other
32:56 . So um quite unusual. So to show you that there are even
33:03 beyond the the quote typical range of 20 or 30 nanometers to about 900
33:11 that we can get into ranges. we're we're getting on the smaller size
33:15 bacteria almost. Okay so um So you can imagine that you can
33:24 at a number of viral features when viruses to kind of classify them.
33:31 Do they have an envelope or What's the nature of the caps?
33:35 symmetrical? Asymmetrical. Isn't filament? is it a federal um What's the
33:43 range is a broad and narrow uh something common in terms of hosts are
33:48 uh What's the virus size. Okay all these directly be used for um
33:55 classification uh is a standard though is called the Baltimore classification. And and
34:03 has to do with the um the used to express the transcript to get
34:14 the M RNA template that can be to express the proteins translate. I'm
34:19 uh transferred into proteins. And so know the terms the plus and minus
34:26 . Right so then the plus RNA what's called a sense RNA.
34:30 Which is essentially the messenger RNA. remember that Plus RNA equals the message
34:37 is the message that can be So we call it the sense
34:40 So it's kind of what? Right the virus take to get to that
34:44 . Okay so for your and so uh seven groups. And so the
34:50 two are DNA viruses whether double stranded single stranded. And they'll follow the
34:58 route DNA RNA. And they'll do using using host RNA polymerase to produce
35:05 transcripts. Okay so that's actually pretty . It's the RNA viruses where it
35:11 get a little tricky. So um so here we have 345 double stranded
35:21 . A single stranded plus RNA single minus RNA. Okay and so the
35:30 he needed here is one that's going be a viral enzyme. Okay the
35:36 will have a gene that will encode it. And these are what are
35:42 RNA dependent RNA polymerase. Is the is found in your cells um is
35:48 called A. D. N. dependent on a plane race. Right
35:52 you don't carry around eukaryotic cells don't enzymes like this because they don't have
35:58 function of copying their RNA into other molecules. We copy DNA and
36:05 So this is gonna be a viral that carries this out. And so
36:10 happens is it enables the RNA virus to copy its RNA genome into uh
36:21 translatable transcript into a sense or plus strand. Okay um and so
36:28 And the unemployment rate is needed for by these RNA viruses. Are these
36:32 groups. Okay so you're the thing remember is that this is all about
36:37 base pairing. So a plus When it's copied reforming minus strand minus
36:45 . When it's copied forms a plus it doesn't matter if you're talking about
36:48 DNA RNA RNA RNA to DNA. . DNA and RNA is all that's
36:55 going to be. That relationship plus copied to a minus minus into a
37:00 . It's just simply the rules of base pairing is why that occurs.
37:05 there's nothing special or unique to It's just it's unique to simulate gasses
37:10 when you copy them it's just the of how it works. Okay so
37:14 a plus RNA virus the memories will produce a minus strand which will then
37:23 used to produce many positive strands. so these are the book will be
37:30 into translated into proteins. Okay and just know that. Um because I'm
37:37 you're thinking well why is it why it need to do that? If
37:41 got a plus strand here right there a plus grand why do we need
37:46 copy? Why can't we just express ? The reason is is because what
37:51 virus is want to do they want replicate themselves and make lots of viruses
37:56 particles. Um It's much more efficient have more than one copy of
38:01 And so you have to remember that particular group for viruses and plus single
38:09 RNA is gonna make lots of viral . Each one of those particles have
38:13 have a plus RNA genome in So we gotta make lots of copies
38:18 that's why we have to go through process. Okay one will not suffice
38:23 need we need hundreds of copies. again for the base pairing rules we
38:28 A plus into a minus minus into plus. Okay and so of course
38:32 gonna generate lots of plus trains. Similarly for the minus single stranded RNA
38:39 . Again yes a virus infects here's genome but we're gonna have to get
38:45 have to get to the plus form that's the one that translates into
38:49 Okay so again here is a step get um on a the independent preliminary
38:57 that into a plus strand. So we can produce its proteins. Okay
39:04 now here's what we put in So groups 34 and five are all
39:11 viruses that required. The only dependent the plan is to get it to
39:18 um plus RNA form that can be to produce the M. R.
39:23 . A. Okay retrovirus is Okay because it takes the route of
39:31 a plus or any virus genome but goes through A. D.
39:34 A. Intermediate and does so using transcriptase. So RNA is copied into
39:39 . N. A. Okay and that is copied into a double strand
39:44 that's using host DNA polymerase to copy minus D. N. A.
39:49 . So again you see the Right? In minus plus RNA is
39:53 in this case to DNA. But a minus strand so it's always the
39:57 . Right? Um And then of the minus DNA is copied into a
40:03 and we have a double stranded And that's really because the retrovirus group
40:08 types that integrate into the host If they're going to do that they
40:12 to have a D. N. . Double stranded DNA A. In
40:15 to integrate into the host chromosome. they've evolved this mechanism to do
40:20 Okay. Um and they can just host preliminaries to transcribe their D.
40:25 . A. Into transcript. So so they don't they don't have retroviruses
40:29 have the need to to to to an RNA dependent RNA polymerase. Okay
40:37 they're gonna make their transcripts from their . N. A. Form.
40:42 so uh so let's just kind of here the two genome types among
40:51 Right. So did you have a virus of course you can serve as
40:57 template for transcription. Right. We're of that DNA to RNA to
41:01 Right. Um can also serve as template for DNA synthesis of course.
41:07 . Through DNA primaries so just like D. N. A. Right
41:13 G. M. A virus that vary, right? It can be
41:16 template for translation. Right. So RNA virus uh can serve as a
41:23 for M RNA synthesis your minus RNA types working services template for D.
41:32 . A. Census. That's your . Right? So depending on the
41:36 viral genome and and the type of it is it can have these three
41:43 roles. Okay, for one of three roles depending on the viral type
41:48 is. Okay. So just just look at the various groups of viruses
41:54 you don't need to memorize this Ah So as mentioned, we have
41:59 group one and two which are DNA double or single stranded. You have
42:04 RNA viruses or different types. And is where we have a lot of
42:09 . A lot of the viruses we are aware of our in these three
42:13 . Okay. Particularly in the single of RNA groups. The plus and
42:17 . So you're measles, mumps, is in their polio virus West Nile
42:26 cold virus uh rabies virus, Ebola . A lot of these things we're
42:34 with are in these route four or . Um The retrovirus is of course
42:41 HIV different leukemias, Religious groups. they're characterized by the reverse transcriptase.
42:47 . N. A. D. . A. Okay. And then
42:50 this other unusual group. Not a of members in it. Hepatitis
42:56 Probably being the most prominent among medically types of infect humans. But the
43:02 of retroviruses. So they actually go it uh have a DNA genome and
43:08 can of course copy that into Just using regular RNA polymerase. But
43:12 they go through uh reverse transcriptase to their army into D. N.
43:18 . Okay. Uh and so that's of a cycle they utilize. So
43:28 use a rough transcript base uh to copies of their genome basically from RNA
43:35 . Okay. Unlike retroviruses which have RNA genome that goes through DNA intermediate
43:41 integrate into the host chromosome. Okay retroviruses are a little different that
43:47 So um so again so in this we'll look at kind of virus definition
43:55 structure of viruses. Uh little infectivity host range. So do or do
44:02 is a difference between host range and . Okay so um how many different
44:09 ? Think of rabies? How many hosts can that virus infect? That's
44:13 range trumpism is within a single How many different cell types can
44:21 Okay so I think of of um is very narrow, very narrow host
44:28 can only affect Cubans and very narrow is um it can only affect a
44:33 type of immune system cell in the . Okay so so just kind of
44:37 those two things straight. Uh Then course look at Bayreuth and primes virus
44:42 primes aren't viruses but they are unique entities ones and infectious RNA ones and
44:48 protein. Okay then we get to at the classification of viruses and the
44:54 there is with the Baltimore system where the standard is how does the
45:06 what's the pathway the virus takes to to an M. R.
45:10 A. That can then be translated proteins. That's that's the route.
45:14 so it doesn't need it may need it. If it's not a virus
45:18 may need this RNA dependent RNA polymerase is going to be a virus synthesized
45:23 virus encoded gene product. Okay um order to copy its RNA genome then
45:34 talk a little about the large viruses are kind of on the uh small
45:39 kind of representing a very large viral infect amoebas and self types of that
45:47 . So um so the next part two will look at the specifics
45:52 different viral life cycles first with bacterial life cycles and then shifting to animal
46:00 life cycles and seeing differences among your and DNA viruses. Animal viruses,
46:06 and DNA type animal viruses and how may differ in terms of their life
46:10 . Okay. Thanks folks. And catch you at the next
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