Polymerase chain reaction (PCR) is a revolutionary method developed by Kary Mullis in the 1980s. PCR is based on using the ability of DNA polymerase to synthesize new strand of DNA complementary to the offered template strand. Because DNA polymerase can add a nucleotide only onto a preexisting 3'-OH group, it needs a primer to which it can add the first nucleotide. This requirement makes it possible to delineate a specific region of template sequence that the researcher wants to amplify. At the end of the PCR reaction, the specific sequence will be accumulated in billions of copies (amplicons).
PCR consist of three main stages: Denaturing – when the double-stranded template DNA is heated to separate it into two single strands. Annealing – when the temperature is lowered to enable the DNA primers to attach to the template DNA. Extending – when the temperature is raised and the new strand of DNA is made by the Taq polymerase enzyme.
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