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Current time:0:00Total duration:5:10

Video transcript

so in this video I'm going to be talking about something known as a southern blot so a southern blot basically allows you to visualize a specific piece of DNA that you're interested in so let's imagine that we have a cup and it's filled with DNA so it's got just a whole bunch of DNA inside and there's just lots and lots of this DNA and let's imagine that I'm specifically interested and once this one gene so let's imagine that I'm interested in gene a and I want to see if gene a is inside of this cup if it's inside of this long piece of DNA now in order to figure out whether or not gene a is inside this cup basically we have to do this process known as a southern blot and we'll break it up into a couple of different steps so step one what we're going to do is we're going to take this DNA and we're going to cleave it so take the DNA and cleave it so let me draw that out so we're going to take this big old strand we're going to remove it outside of the cup over here so we've got this big strand and we're going to cut it up we're going to expose it to enzymes that will basically cleave the DNA and a whole bunch of different parts and that will result in lots of these smaller pieces of DNA and so that's basically the first step so we've got a bunch of small little pieces of DNA now step two what do we do well what we're going to do is we're going to take all these tiny little DNA fragments and we're going to run them on the gel so specifically we're going to do a gel electrophoresis electrophoresis on these DNA fragments and I made a video on gel electrophoresis so if you want to refresh you can watch that video but basically the gel electrophoresis will help us separate these DNA fragments based on size and based on charge so let's just diagram that out so we're going to take these DNA fragments and we're going to run them on a gel so let's imagine that this is the gel and we add the DNA fragments to different wells so the fragments are going to move down the gel and they're going to basically be separated based on size and based on charge so we're have these fragments separated like so so now we've got this gel and we've got the DNA fragments separated by size on this gel so the next step step number three is basically we're going to take this gel and we're going to transfer it to a filter so transfer the gel onto a filter and what the filter will basically allow us to do is utilize two visualizes this gel is very flimsy so we want to transfer it onto a filter so what we'll do is we'll take a filter that's basically the same size as the gel and we're going to basically just put it right on top of the gel for a little bit and the fragments will basically transfer onto the filter so now we're going to have a filter with these fragments and the filters a lot sturdier than the gel so this is the filter and I'll just write that down over here and this over here is the gel okay so the next step step number four is we're going to take the filter and we're going to expose it to a radio labeled D piece of DNA so expose to radio labeled DNA now this radio labeled DNA is going to be the complement to our gene of interest so we're interested in finding out of gene a is present in this massive DNA over here so what we do is we're going to take the complementary sequence to gene a and radio label it and expose it to this filter so let's imagine that the radio labeled piece of DNA is this pink piece of DNA and let's imagine that we do have gene a so let's imagine that this piece of this DNA fragment was actually gene a our gene of interest so what's going to happen is when we expose the radio labeled DNA to this filter paper it's going to anneal to our gene of interest so we're going to have this radio labeled piece of DNA stuck to this DNA fragment which is its complement so in order to visualize it in order to visualize this radio labeled piece of DNA we have to do the fifth and final step which is exposed the filter to an x-ray film in order to visualize the radio labeled per so expose to x-ray and the x-ray basically it'll shoot a bunch of x-rays and since this piece of DNA is radio labeled it will pop up on the x-ray film so we're going to have a film and we'll draw that film over here so we'll have this film basically the only thing that will pop up is this fragment over here and that fragment will have a control we'll be able to say okay well since we have this fragment it's basically the radio level piece of DNA and since we see the radio label DNA it means that it had bound it was bound to this gene a which means that gene a was in this cup of DNA