Taq Polymerase: Definition & Function

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  • 0:00 What Is PCR?
  • 3:05 Enzymes
  • 3:30 Environment is Everything
  • 5:05 What Does Taq Do?
  • 6:20 Lesson Summary
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Lesson Transcript
Instructor: Adrienne Brundage
In this lesson, we will learn about Taq polymerase and how it is used to amplify segments of DNA in the lab. We will discuss who discovered it, the method, and its function.

What Is PCR?

Imagine you're a scientist in the mid-1980s, trying to figure out how to copy lots of DNA all at once. The idea that we could use DNA for anything has only been around for a few years, and there you are, driving up the coast of California, musing on how to make your job easier. Suddenly it hits you - what if you could copy tiny parts of the huge DNA molecule really quickly, just like using a photocopier to duplicate a page in a book? That would sure make your life in the lab much more pleasant! Well, that's how Kary Mullis helped advance the science of DNA by advancing the science of PCR.

PCR is short for polymerase chain reaction and is a method we can use to clone sequences of DNA. We often want to clone these sequences a lot (on the order of a billion copies of a single sequence!), so technology is obviously involved. This is how it works:

DNA is collected from somewhere. Then we take that DNA and break it apart. Knowing what we know about the structure of DNA makes this process simple. The two complementary strands of DNA are attached via bonds. Heat can break those bonds. This is one of the reasons living things can only tolerate so much heat - DNA actually breaks apart.

PCR is the amplification of specific regions of DNA. First, we need to break up the double strands using heat. As luck would have it, we know that heating DNA up to around 94° C will cause DNA bonds to rupture, and we'll be left with a single-stranded DNA.

Once we have our single strand, we need to focus in on just the region we want. Imagine wanting a single page of a book but photocopying the whole thing! That wouldn't do. PCR is basically focusing on one page and photocopying it over and over again. To do that with DNA, we need to tell the DNA what to replicate, and then give it the means to do so. We do this by using enzymes and primers.

Primers are a subject for another time, but they are responsible for telling the polymerase where to do its work. Think of them like the bookmarks you use to remember which page you want to photocopy. Primers help the enzymes focus on a particular section of DNA so the entire thing doesn't get copied.

The next step in PCR is actually making a new strand of DNA. Have you ever tried doing really delicate work when it's really hot out? DNA can't replicate at that high temperature of 94° C, either, so in order for PCR to continue, we have to cool it down a bit, to 72° C, to be exact. That's still pretty toasty at about 160° F, but most enzymes work well at that temperature, especially those that replicate DNA. However, most enzymes can't stand that super-high temperature of 94° C and end up melting apart, just like DNA. That was an issue with early PCR methods, and one that we found a solution to in nature. Let's focus on those enzymes!

Enzyme

Enzymes are proteins that speed up reactions without being consumed themselves. The most important enzyme in a PCR reaction is called taq polymerase. A polymerase is an enzyme that attaches molecules together, and we just so happen to want to attach many nucleotides (the building blocks of DNA) together, so it works out for us.

Every cell that has DNA has its own polymerase that takes care of replication of DNA. PCR uses a polymerase from a species of bacteria, Thermus aquaticus, which normally lives in hot springs.

Environment is Everything

Have you been to any hot springs? They are ridiculously hot, yet some bacteria are able to survive very well under these steamy conditions. Why is this important? Well, cells that live happily at lower temperatures have enzymes that work perfectly at lower temperatures. If the temps get too high, the enzymes denature, or lose their structure, and no longer work.

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