What is PCR - Polymerase Chain Reaction

PCR (Polymerase Chain Reaction) is a technique to copy DNA in a test tube. DNA is mixed with reagents and placed the test tube is placed in a thermal cycler. Thermal cycler enables the mixture to be incubated at a series of temperatures that are varied in a preprogrammed manner.

Following are the steps:

  1. Heat the mixture to 94 degree Celsius to break H bonds that hold the double strand together. This is called denaturation.
  2. Cool the mixture to 50-60 degrees. The strands can join back together at this temperature but they won't due the heavy presence of oligonucleotides or primers which anneal to the DNA molecules at specific positions.
  3. Temperature is raised to 74 degrees, which is optimum temperature for Taq DNA polymerase which is present in the mixture. Taq DNA polymerase attaches to one end of each primer and synthesizes new strands of DNA, complementary to the template DNA molecule. Thus we now have 4 strands instead of 2.
  4. We then increase the temperature back to 94 degrees and denature to repeat the process. At the end of this step, we would have 8 DNA strands. We continue until, the DNA is sufficiently amplified.

Source: Gene Cloning & DNA Analysis by T. A. Brown

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