How do we separate the different pieces of DNA
that we've cut up and that we've joined?
Now to do that, we use a technique for separating molecules of different sizes
that is widely used in biological work, that depends on electricity.
And we've got an example of it here.
You see in this box, we've got a gelatinous surface,
you can see it, the grey material, on a glass plate.
And it's bathed in a liquid.
And we've got a negative and a positive charge here going through.
So that electricity is running through that liquid.
So if we put things at one end, they're subject to an electric current.
So Nigel is going to give me this pipette
and I'm going to put a little bit of the material in just into these slots here at this end.
Just a little bit in there.
Now.
What's going to happen is the electricity is going to run through that.
And while that's happening let's explain the basis on which that can separate molecules.
So you see what we've got here is, we've got a negative and a positive,
in our solution.
And the current can flow from the negative to the positive.
And we put in that a mixture of molecules, big ones and little ones.
So as the current flows, what happens? The molecules they move along.
They move along.
But the little ones move quicker than the big ones.
So after a period of time we've separated them.
The little ones have moved further than the big ones.
We've separated out molecules of different size.
Now we set up an experiment like this a little earlier,
so that you could see just exactly what happens.
And here is the gel on this lectern.
And you can see the gelatinous material on the glass slide.
And you can see the separation now of three different dyes.
The blue, the purple, and the yellow.
That's what happened when we let
that electric current run through a period of time
to separate out those molecules of different size.
And that's the principle on which we separate out the DNA molecules of different size
that arise when we cut a DNA molecule up.
So we're going to show you a picture of such an experiment
in which we've cut a DNA molecule into several pieces.
And then we've separated the pieces according to size using this technique.
I'm putting these gloves on because we've stained the DNA with a chemical stain
and we've got to be careful when handling this.
And that's why Nigel and I are wearing these gloves.
And we're sliding this... we'll slide this onto here.
Slide it onto here.
And what we're sliding it onto is a UV light.
A source of UV so I'm, because I'm looking at this from close up,
I'm going to put on these spectacles to protect myself from the ultraviolet light.
Now we'll switch on the ultraviolet light.
And the ultraviolet will fluoresce the samples of DNA that have picked up the dye.
Can you see that?
Can you see here these three columns here?
You see these three? That's the DNA that's not being cut with the enzyme.
When we cut the DNA with one of those enzymes, we cut it into several pieces,
and we separate out the pieces.
One there. One there.
Can you see those pieces?
We've separated those pieces by this technique of electrophoresis
into their different parts, into the parts into which they're been cut by the enzyme.
Now we can take those pieces out from the gel and use them for our experiments.