PCR POLYMERASE CHAIN REACTION

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Learn about PCR and how it is used to make many copies of DNA for crime scene investigations (and other applications). • Transcript: • Imagine that you are investigating a crime scene and only find a tiny drop of blood or a hair follicle as clues. Although these pieces of evidence have DNA, they only have a very small amount, not nearly enough to deduce who they belong to. So how can you get enough DNA from this evidence to help solve the crime? • The answer is PCR, or Polymerase Chain Reaction. • PCR is an important biotechnology technique that allows us to make many copies of DNA. Essentially PCR is DNA replication in a test tube, and it allows us to get sufficient DNA to determine which suspect was present at the crime scene. • Here’s how PCR works: • A special microfuge tube called a PCR tube is filled with all the stuff that you will need to copy the DNA of interest. This includes: • 1. The crime scene DNA you wish to copy. • 2. DNA nucleotides (these are the building blocks of DNA that will be used to build our copies). • 3. Primers (these are needed to get the process started). • 4. A special form of DNA Polymerase that tolerates high temperatures known as Taq polymerase. Taq polymerase comes from a bacterium that lives in hot springs with nearly boiling water. Since PCR uses high temperatures, this type of DNA polymerase is necessary. Other types of polymerase would denature at these high temperatures. • Once all of these reagents are added, the PCR tube is placed in a PCR machine, also known as a thermal cycler. • Inside the PCR machine, the DNA is heated, breaking the hydrogen bonds that hold its two strands together. • The machine then cools down the reaction mixture. This allows primers to attach to the ends of the DNA segment that we want to copy (which is usually a region that varies a lot between different individuals). • Now that the primers are attached, we can use Taq polymerase and nucleotides to build new DNA strands. The PCR machine raises the temperature to the optimal temperature for Taq polymerase, so that this enzyme can get to work. Nucleotides are added following base-pairing rules, just like in normal DNA replication in a cell. • This process of heating and cooling the PCR mixture is repeated many times, and every time it is repeated the amount of DNA doubles. This can make a lot of DNA. After 30 cycles, for example, a single molecule of DNA can become over a billion (with a B) copies! • This amount of DNA is plenty to be able to analyze using other techniques like gel electrophoresis so that we can determine whose DNA it is. • Music: • Dark Trap | DARKNESS | by Alex-Productions | / @alexproductionsnocopyright • Music promoted by https://www.free-stock-music.com • Creative Commons Attribution 3.0 Unported License • https://creativecommons.org/licenses/... • Hot Spring Photo: Freeimages.com/tijmen • PCR Tubes image: Madprime, CC0, via Wikimedia Commons https://commons.wikimedia.org/wiki/Fi... • Thermal Cycler Image: Karl Mumm, CC BY-SA 3.0 https://creativecommons.org/licenses/..., via Wikimedia Commons. https://commons.wikimedia.org/wiki/Fi...

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