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We're on next lesson. DNA technology with Dr. Ruth Tennen.

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Another subtopic. How does the polymerase chain reaction or PCR work?

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Great, so polymerase chain reaction or PCR is a way of amplifying DNA, starting from a very small number of molecules.

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And it happens in three steps. So the first step is you heat up the DNA. It's called denaturation.

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Amplifying pieces of DNA. Amplifying meaning making them bigger? Louder?

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Making more copies of the same thing.

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So you've got this denaturation step. Basically, you heat up the DNA, it separates the two strands.

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The next step is called annealing. You lower the temperature.

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And what happens here is you have little DNA primers, which are similar to the RNA primers we talked about before during replication.

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These DNA primers sit on either end of the gene that you're interested in, and they basically get things started for DNA polymerase.

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So in the third step of the reaction, when you increase for the extension, the polymerase binds

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and it extends those primers, and goes across. So basically what you're doing is you're starting off with a single molecule of DNA...

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and after one step, you get two molecules of DNA. So it's a way of amplifying every time by a factor of two.

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Yeah, so you can imagine that most proteins don't like getting heated up.

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...to 95 degrees Celsius over and over. It's a thermostable, it's called.

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So it's basically from a bacteria that lives in heat vents, and so it has no problems being hot for long periods of time. It's a special polymerase.

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What is the end game here in making all these copies?

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The basic reason is because it's really hard to work with single molecules of DNA.

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So for example, if you wanted to figure out the sequence of a piece of DNA from one of your cells, it's a lot harder to do that if you only have one copy...

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versus if you could make multiple copies. So it helps with that.

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It also helps if you wanted to clone. You can't really clone very well with a single piece of DNA, but if you had multiple copies, it would be much easier to do that.

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Then we combine the multiple pieces back together, and that's what's called recombinant DNA?

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Recombinant DNA is actually...you take a single one of those copies and put it into a new backbone.

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So recombinant basically means you're taking DNA from two different sources and putting them into one place.

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Give us an example. Like, walk us through one slip of DNA that would be an obvious use case.

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So one really cool thing that scientists have done is for people who have diabetes...they need to get insulin.

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They used to get it from pigs and cadavers, which is not ideal for many reasons.

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And so you can actually take the human insulin gene that you made through, say, RTCPR...

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and you insert it into a backbone, and then you put it into bacteria, and then the bacteria will make the insulin for you.

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