Polymerase chain reaction (PCR) is a method widely used in molecular biology to rapidly make millions to billions of copies of a specific DNA sample allowing scientists to take a very small sample of DNA and amplify it to a large enough amount to study in detail. PCR was invented in 1983 by Kary Mullis. It is fundamental to much of genetic testing including analysis of ancient samples of DNA and identification of infectious agents. Using PCR, copies of very small amounts of DNA sequences are exponentially amplified in a series or cycles of temperature changes. PCR is now a common and often indispensable technique used in medical laboratory and clinical laboratory research for a broad variety of applications including biomedical research and criminal forensics.

A basic PCR set-up requires several components and reagents, including:

1. a DNA template that contains the DNA target region to amplify
2. a DNA polymerase; an enzyme that polymerizes new DNA strands; heat-resistant Taq polymerase is especially common, as it is more likely to remain intact during the high-temperature DNA denaturation process
3. two DNA primers that are complementary to the 3′ (three prime) ends of each of the sense and anti-sense strands of the DNA target (DNA polymerase can only bind to and elongate from a double-stranded region of DNA; without primers there is no double-stranded initiation site at which the polymerase can bind);specific primers that are complementary to the DNA target region are selected
4. deoxynucleoside triphosphates, or dNTPs (sometimes called “deoxynucleotide triphosphates”; nucleotides containing triphosphate groups), the building blocks from which the DNA polymerase synthesizes a new DNA strand
5. a buffer solution providing a suitable chemical environment for optimum activity and stability of the DNA polymerase
6. bivalent cations, typically magnesium (Mg) or manganese (Mn) ions; Mg2+ is the most common

The basic steps are:
1. Denaturation (96 °C): Heat the reaction strongly to separate, or denature, the DNA strands. This provides single-stranded template for the next step.
2. Annealing (55- 65° C): Cool the reaction so the primers can bind to their complementary sequences on the single-stranded template DNA.
3. Extension (72 ° C): Raise the reaction temperatures so Taq polymerase extends the primers, synthesizing new strands of DNA.

Assets

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