Bacteriophage: Lysogenic Phage Infections

in this video, we're going to continue to talk about bacteria pages by focusing specifically on lyssa genic fage infections. And so first recall from our previous lesson videos that Lissa genic fe ages are also sometimes referred to as temperate pages. And these pages may not immediately produce neuf ages. And so after Lissa genic fage D. N. A enters into a host cell, one of two possible scenarios are going to happen. And so the first scenario is that after injection of the Lissa genic fage D. N. A, it could lead to the production of new pages by the lyric cycle, as we already discussed in our previous lesson videos. But the second possible scenario of the Lissa genic fage D. N. A is that it could lead to integration of the fage DNA into the host chromosome forming what's known as a pro fage. And recall the profile page is just the fage DNA that has been integrated. And so this occurs by the Lissa genic cycle. And so the list eugenic cycle or list. So ginny is the Lissa genic fage replicating where the fage DNA remains silent or inactive in the cell. And so new fe ages are not being produced. However, the pro fage the integrated fage D. N. A. Can replicate inside of the Lissa gin. And so recall that the lycee gin is just the bacterial cell that carries the pro fage the integrated fage DNA. And so the pro fage which is within the chromosome of the host cell can be replicated as the host cell replicates. And so the pro fage can be passed down to future generations of the bacteria through the normal replication processes. And so if we take a look at our image down below, we can get a better understanding of the Lissa genic cycle as it occurs in a specific type of bacteria fage known as the land of age. And so what you'll notice here is the very top we're showing you bacteria fage attachment and genome entry where the bacteria fage is able to attach to the surface of the bacteria and then inject its genome into the fage. Now, if this is a temperate or a Lysa genic fage, then the fage uh could lead directly to the lyrics cycle as we talked about it previously. However, it could also go into the Lissa genic cycle. And in the list of genic cycle, what we have is integration would be the third step after genome entry. And of course in integration what happens is the fage D. N. A. Is going to integrate into the host cell's chromosome forming a pro fage. And so the profile page is really just the integrated fage DNA. And the bacterial cell along with the pro fage is referred to as a Lysa gin. And so this is where the Lissa genic cycle gets its name from. Because elissa gin is a bacterial cell that contains a profile page Now as the lice engine begins to replicate and divide, it will also replicate and divide the profile page as well. And so notice that the pro fades here is also being replicated and passed passed down. And so the pro fades replicates with the host chromosome with the license gines chromosome. And so what you'll notice is that all of the cells that result from replication are going to contain the profile page as well. And so the viral pro fage, the integrated viral DNA is being replicated and passed down to the future generations of cells and so all offspring are going to end up being license because they all contain the pro fage. Now, what can happen under the right conditions is the pro fage is able to x ice itself. And so that leads us to the fifth step excision and excision is really just the removal of the fage DNA. And so the excited fage D. N. A. Is when this profile page here is able to excite or remove itself and the pro phase can be excited by a viral enzyme and that can allow the lyrics cycle to begin. And so what this means is that the lice a genic cycle has the ability to transition back into a lyric cycle and it can ultimately cause the cell to lice and lead to a productive infection. However, the Lissa genic infection here notice that there are no viruses being produced in this period. Only the pro fage is being replicated. The integrated fage D. N. A. And so we'll be able to get some practice applying these concepts as we move forward in our course. But for now, this year concludes our brief introduction to the Lissa genic fage infections, so I'll see you all in our next video.

in this video, we're going to introduce Lissa genic conversion. And so Lissa genic conversion is really just a finna typically change of a lice a gin based on the profile page that it carries. And so once again recall from our previous lesson videos that a profile page is really just the integrated fage D N A. And the lice A gin is the cell that contains the profile page. And so once again listen, Jenna conversion is really just when the lice a gin changes, it's finna type due to the integrated fage DNA, the pro fage now typically Lissa genic conversion can result in the change of the host cell surface structures. And once again these host cell surface structures is what the fe ages rely on to attach and initiate an infection. And so by changing the host cell surface structures, the fage is will not be able to attach and so through this cells can become immune to what is known as super infection. And super infection is really just infection by the same type of fage. And so life's agenda conversion when it changes the host cell surface structures, the same fage will not be able to infect the cell. And so the cell the lycee jin becomes immune to super infection. Now, occasionally, in some cases Lissa genic conversion can also give the cell disease causing properties for example, the synthesis of a toxin, the ability to synthesize a toxin. And so if we take a look at our image down below, we can get a better understanding of Lissa genic conversion. And so notice on the left over here we're showing you a bacterial cell and before an infection a viral infection uh we have a bacterial cell with the normal phenotype. However notice that when a bacteriophage virus comes and infects the cell and injects its genome. That genome occasionally can insert itself into the chromosome to create a profile page which is what we're showing you here. The profile page is the integrated fage DNA. And so notice that the surface receptors okay of this lice a jinn are capable of being converted through Lysa genic conversion to alter the phenotype. And so notice over here we have an altered phenotype where now the surface structures are being altered through the pro fage. And so the alteration of the surface structures makes it so that the same fage is not able to bind and induce an infection. And so this Lissa gin with altered phenotype due to Lissa genic conversion is going to be immune to a super infection or immune to infection by the same fage. And so in addition to super infections, sometimes Lissa genic conversion can give these lice engines disease causing properties like for example the ability to synthesize a specific type of toxin. And so this year concludes our brief introduction to Lissa genic conversion and we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video