- So in this video, I'm gonna 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 those DNA
and let's imagine that I'm specifically
interested in 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 1, what we're gonna do
is we're gonna take this DNA
and we're gonna cleave this.
So, "take the DNA and cleave it."
So, let me draw that out.
So, we're gonna take this big old strand.
We're gonna remove it outside of the cup over here.
So, we got this big strand
and we're gonna cut it up.
We're gonna expose it to enzymes
that will basically cleave the DNA
in a whole bunch of different parts.
And that will result in lots
of these smaller pieces of DNA.
So that's basically the first step.
So we got a bunch of small little pieces of DNA.
Now Step 2, what do we do?
Well, what we're gonna do is we're gonna
take all these tiny little DNA fragments
and we're gonna run them on the gel.
So, specifically we're gonna do
a gel electrophoresis, "electrophoresis"
on these DNA fragments.
And I made a video on gel electrophoresis
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 gonna take these DNA fragments
and we're gonna 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 gonna move down the gel
and they're gonna basically be separated
based on size and based on charge.
So, we're gonna 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 gonna take this gel
and we're gonna transfer it to a filter.
So, transfer the gel onto a filter.
And what the filter will basically allow us to do
is it allow us to visualize
'cause this gel is very flimsy.
So, we want to transfer it onto a filter.
What we'll do is we'll take a filter
that's basically the same size as the gel
and we're gonna basically just put it
right on top of the gel for a little bit
and the fragments will basically
transfer on to the filter.
So now, we're gonna have a filter with these fragments
and the filter is 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
that we're gonna take the filter
and we're gonna expose it to a radio-labeled
the 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
if Gene A is present in this mass of DNA over here.
So what we do is we're gonna 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 or our gene of interest.
So what's gonna 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 gonna have this radio-labeled
piece of DNA stuffed to this DNA fragment
which it's 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 expose the filter to an x-ray film
in order to visualize the radio-labeled probe.
So, "expose to x-ray."
And the x-ray basically it will 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 gonna have a film and we'll draw
that film over here so we'll have this film
and basically the only thing that will pop up
is this fragment over here
and that fragment will have a control
and we'll be able to say,
"Okay. Well, since we have this fragment
"it's basically the radio-labeled piece"
"of DNA and since we see the radio-labeled 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."