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Current time:0:00Total duration:5:11

Viral replication: lytic vs lysogenic

Video transcript

so let's talk about viral replication since we know that viruses are made of only proteins and one type of nucleic acid which means they have no organelles to make copies of themselves with they have to get inside other cells in order to use their ATP and their organelles to make copies of themselves so first step get inside that cell and I'm just going to mention a few things for review so remember there are three ways of getting into a cell you know one of the ways of getting in is that bacteria phages they literally just inject their genetic material inside of the cell whereas every other type of virus uses one of two ways they if they're not envelopes they they trick the cells receptors into letting them in or if their envelope they can either use that receptor trick or they directly fuse with the membrane and once that genetic material is inside of the cell the virus has hacked in and it's ready to do a takeover but here's where it makes a choice it's kind of either impatient and ready to get going to copy itself or it sits back and says you know what I'd rather sit and wait until I'm ready to take over so let's just draw these two possibilities out to see what happens and with the first choice the the impatient virus goes ahead and takes over the cells machinery they're their ATP ribosomes nucleic acids amino acids to start making copies of the virus's genetic material which again can be RNA or DNA and also the viruses proteins to make their protein coat and these will self assemble that means they just come together on their own to form fully functional viruses and because it keeps making more and more and more of these it will eventually force the cell to lyse or break open and once it breaks open all of these viruses are released into the environment and if there are other cells nearby then this army can start marching out to infect to hack into those nearby cells and create more armies so this makes a lot of sense if you have a lot of hosts around and your goal is to just create the biggest army in the fastest way possible and so that's the impatient virus so what about the other option the other option is where the virus decides it's just going to sneak in and hitch a ride it thinks that the bacteria seems to be doing fine on its own maybe there aren't other hosts nearby so there's no reason to kill off the host because lie sing it would kill the host so we don't want that we're just going to keep the host alive and in order to sneak in and and let the bacteria do its thing while it's waiting it's going to combine with the hosts genetic information so that the hosts really can't tell that it's there it's basically quietly sitting there because it's repressed there are repressor genes on this virus so it's not expressed it's not transcribed so it's not doing anything and this is called a pro virus or you might also hear the word Pro fade and again because it's not doing anything this is called a dormant or latent phase so the bacteria just does its own thing it continues replicating and of course the virus is already there so it will continue to replicate so it will replicate when the bacteria does because it's part of its genome but about one in 10,000 times that this happens or if something happens like the bacteria is exposed to UV light or something well in any case there's something that weakens that repressor gene that we talked about on that virus so it's no longer quiet and the hosts genome like most other genomes will start wanting to repair itself that means it will cut out to try to repair its genome it will excise out part of its DNA that just happens to be the virus and now the virus is active it's ready to make copies of itself lyse the cell and get its army out into infecting other cells so the official terms for the impatient method is the lytic cycle and the hitch a ride method is called the lysogenic cycle so now you should have a good idea of what the lytic and lysogenic cycles are in viral replication
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