Hi. In this video, I'm going to be talking about nucleic acid hybridization. Hybridization is a process that takes advantage of the fact that nucleic acids, especially complementary nucleic acids, such as A or T, C and G, will form bonds with each other. Knowing that, you can perform two different techniques. The first is Southern blotting, and this is used to detect specific genes in cellular DNA.
How you do this is you take DNA from an organism, and then separate it by gel electrophoresis, which, if you don't remember is fine, but this is going to be separating via mass. Then you transfer that onto some type of paper, and then incubate that paper or set that paper in a solution with a DNA probe. This DNA probe is going to be complementary to a sequence that you're interested in. So, let’s say you need to know if the ATCGGAT sequence is present in the cell. What you do is you take the DNA, you run it, you say, okay, this size will run at 7 base pairs. You take that and then incubate it with a probe that would be TAGCCCTA because it's complementary. And, if it binds, then that means it's there.
You typically fix this probe with some type of fluorescent material, or it can be radioactive material. So if you have that on the paper and you incubate the probe, the probe will bind to the sequence if it's there. And that way, when you detect it you'll see this fluorescence. But if it's not there, that sequence isn't present, it won't bind, and there will be no fluorescence. The same technique can be done with Northern blotting, but this uses RNA instead of DNA.
This is what this looks like: This is an example of Southern blotting. You have two DNA sequences you are interested in looking at. You have one that is 5 kilobases and another that has 23 kilobases. You take, you isolate the DNA, you run it on a gel, which is in this box here, and then you incubate it with a probe that has a complementary sequence. And what you'll see is that if these sequences are present, then you'll see them. Here we have A, the sequence is present at 5, and B, the sequence is present at 23.
That’s Southern blotting and Northern blotting as well. It's just done with RNA for Northern blotting. So with that, let’s now move on.