Polymerase chain reaction
Polymerase chain reaction, or PCR, refers to a method of heat cycling to amplify DNA. It was made possible by the discovery of a thermophilic (heat loving) bacterium: thermus aquaticus. The DNA polymerase from this bacterium made DNA replication at high temperatures (60-70 degrees Celsius) possible.
PCR works by the cycling of several temperatures:
- a melting period, usually set at a high temperature (anywhere between 70 and 90 degrees Celsius)
- an annealing period, set at a lower temperature (anywhere between 45-55 degrees Celsius)
- an elongation period, set at a moderate temperature (anywhere between 60-70 degrees Celsius)
After an initial denaturing period, these three periods are cycled anywhere between 10 and 30 times, using various lengths for each period depending on what the researcher is working with. Most PCR machines will, after reaching the end of the cycling and completing the final elongation phase, hold the DNA at a very low (comparatively) temperature of 2-4 degrees Celsius for an infinite time, or until the researcher removes the DNA from the machine.
- Bartlett & Stirling (2003)—A Short History of the Polymerase Chain Reaction. In: Methods Mol Biol. 226:3-6