18. Viruses, Viroids, & Prions
Introduction to Bacteriophage Infections
Map of Lesson on Bacteriophage Infections
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in this video, we're going to begin our introduction to bacteria fage infections. And so first we need to recall from our previous lesson videos that bacteria pages are also sometimes referred to as fe ages. And so these bacteria pages are pages recall these are viruses that specifically infect bacterial cells and also recall that these bacteria phages can serve as a vehicle for horizontal gene transfer through trans direction. Now these fage infections can actually occur in a variety of different ways. And as we move forward in our course, we're going to talk about some of those different ways in which bacteria phages can infect cells. And so down below what we have is our map of the lesson on bacteria fage infections which is this image that you see down below. And so because this is a map of our lesson, you can actually use this map to help guide you as we move forward in our course talking about fage infections. And as always we're going to be exploring this map of our lesson by exploring the left most branches first and then zooming out to explore these branches in this order from left to right. And so what you'll notice here in this map is that fage infections can be categorized as either productive infections that cause cell death or they could be categorized as productive infections that do not cause cell death or these fage infections could be latent state infections. Now in terms of the productive infections that cause cell death, these include lyric or virulent fae ages. And in these pages, what we're going to see as we move forward in our course and talk more about them is that it causes the host cell to lice. And so when the host cell lice is, it ruptures and bursts and the fe ages can be released. And so that's what we're seeing here is that the host cell is rupturing open and all of the bacteria phages can be released in this way as the cell is dying now for these latent state infections, these are going to be caused by lizzo genic fage is also known as temperate fe ages. And these lice eugenic phase is what we're going to see is that they are going to integrate silently into the host chromosome. And occasionally they will be able to cause something known as lisa genic conversion, which we will get to talk more about later in our course as we move forward in our course. But that is going to help prevent something known as super infection. And so again, we'll be able to talk more details about this later in our course as we move forward and then last but not least the last section of our map, we're looking at productive infections that do not cause cell death. And this includes filament tous pages. And so these filaments pages are going to be able to infect the host cell via the pill. I of the hosts up and so down below you can see a filament is fage infecting the host cell via its pillow. And once again, we'll be able to talk more about these filaments ISF ages uh and all of these different types of fage infections as we move forward in our course. But for now, this year concludes our brief introduction to bacteria fage infections. And once again, we'll be able to learn more about each of these pages in their own separate videos as we move forward in our course. So I'll see you all in our next video.
Productive vs. Latent State Infections
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in this video, we're going to distinguish between productive infections and latent state infections. And so really there are two main types of fage infections. Once again, there are productive infections and there are latent state infections. Now the productive infections as its name implies, new fage particles are going to be produced. And so the production of these new fage particles during a productive infection could potentially kill or lice the cell when the cell ruptures, releasing viruses. Or on the other hand, a productive infection may not kill the host cell and so it's possible to host cell does not die, but it will continuously release and produce viruses. And so regardless if this host cell dies or not, productive infections are going to produce new fage particles. Now, during a latent state infection, the viral genome is going to silently integrate into the host cell's chromosome. But during a latent state infection, there will not be the production of any new fage particles. And so during a latent state infection, when the viral genome silently integrates in the host chromosome, the integration of the viral genome can change the genotype of the host cell. And by changing the genotype, of course, that's going to be changing the set of genes that it has. And also the viral genome that has been integrated into the host cell's chromosome can replicate as the host cell multiplies and divides into more cells. And so if we take a look at our image down below, notice the left hand side of the image is focusing in on a productive infection and so productive infections may or may not kill the host cell but which will notices during productive infections. New fage particles are going to be produced. And those fage particles once again it may kill or rupture or lice the cell releasing fage particles or it may not kill or rupture the cell. Um But new fage particles are going to be produced during a productive infection. Um And so on the right over here. What we're focusing in on is a latent ST infection. And during the latent state infection when the bacteria fage infects the bacteria, what you'll notice is that the fage genome is going to integrate into the host cell's chromosome. And so you can see the integrated fage D. N. A. Is being pointed out right here in this image. And so when the fage D. N. A. Is integrated like this, the uh cell is not going to be producing new fe ages. And so the host cell is going to uh basically host the viral genome and the viral genome is going to be silently integrated into the host cell's chromosome. And so the integration of the viral genome here once again can change the genotype of the host cell. And so it could give the host cell new properties. Um but the viral genome can also replicate as this host cell multiplies as well. And so we will get to learn and talk more about productive infections and latent state infections as we move forward in our course. But for now, this here concludes our brief differentiation of productive and Layton state infections. And once again, we'll be able to get some practice applying these concepts and learn more as we move forward in our course. So I'll see you all in our next video.
Some viruses, such as human herpesvirus 1, infect a cell without causing symptoms; these are called:
Lytic & Lysogenic Bacteriophages
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in this video we're going to differentiate between lyric and Lissa genic bacteria pages. And so lyric fe ages are also sometimes referred to as virulent fae ages And these are bacteria pages that can cause a productive infection and this productive infection specifically will kill the infected host cell by cell like ISIS. Now listen to genic fage is, on the other hand, are sometimes referred to as temperate fage is. And so these Lissa genic, or temperate fage is our bacteria pages that can carry out a productive infection or they could carry out a latent state infection. And so we'll be able to learn more about these lice, a genic and temperate pages as we move along. But there are a few things that you should note here and that is that the fage DNA of a Lysa genic or temperate fage has the ability to integrate itself into the host chromosome, creating what scientists refer to as a pro fage. And a pro fage is really just the integrated fage DNA. And so this creates what is called a Lysa gin and a list login is a cell uh that is carrying a pro fage. And so this pro fage, the integrated fage DNA can either remain integrated indefinitely for long periods of time or the pro fage can actually excites itself or remove itself from the host chromosome in order to begin a lyric or productive infection. And so if we take a look at our image down below, we can get a better understanding of this and so notice at the top, we're showing you bacteria fage attachment where a bacteria fage like this one here is able to attach itself to a bacterial cell and the fade will inject its DNA into the host bacteria. And so if it is a little fage then it will be able to conduct the lyric cycle. And as the lyric cycle implies with the term lyric uh it is going to be a productive infection where new viruses are going to be made and it is going to occur result and sell license. And so you can see the lyric here in the lyrics cycle is for the uh license that occurs to sell rupturing. And so notice that these bacteria pages are being produced, making it a productive infection. And it does indeed lice and kill the cell. And so all the pages are able to be released through license. Now, if it is a Lysa genic or a temperate fage then it will induce the lice a jet or it can induce the light psychogenic cycle. And so in the list eugenic cycle, which will notice is that the injected fage D. N. A. Has the ability to integrate itself into the bacterial chromosome to create a pro fage. And once again, the profile page is really just the integrated fage DNA that has integrated itself into the host chromosome. And so once the fate has integrated itself into the host chromosome it can then be replicated alongside the host chromosome and be passed down to future progeny. Uh and uh it is possible for this profile page to excite itself to remove itself and to shift into a lyric cycle. And so that is what this green arrow that you see here over towards the lyric cycle represents. That a page that is Lissa genic is able to integrate to create a profile page. And the cell that contains the profile page is called a Lysa gin, like what we mentioned up above in our text. And so this profile page again has the ability to x ice itself, remove itself and to initiate a lyric cycle. And so we'll be able to talk more about this idea here as we move forward in our course. But for now, this here concludes our brief introduction to lyric bacteria pages and Lissa genic bacteria pages. And so I'll see you all in our next video.