Polymerase chain reaction, or PCR, is a method scientists use to make millions of copies of a segment of DNA. Polymerases -- a type of enzyme protein -- help to build the new segments. Scientists often use the Taq polymerase in PCR.
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Taq polymerase comes from the bacterium Thermus aquaticus, which lives in hot springs. Kary Mullis and Fred Faloona originally developed PCR in the mid-1980s using a polymerase from Escherichia coli, but scientists soon began using Taq in PCR because it was more suitable for high temperatures.
PCR involves denaturing, annealing and replication steps, usually repeated 20 to 30 times. Denaturing separates the double-stranded DNA into single strands. In the annealing step, primers bind to the segments of DNA to be copied. Taq polymerase goes to work in the replication step: the polymerase builds each single strand of DNA marked by a primer into a new, double-stranded DNA segment.
The high temperatures required to denature DNA destroyed the E. coli polymerase originally used in PCR, requiring new polymerase to be added after each PCR cycle. Taq polymerase can withstand these temperatures, so scientists can now run many PCR cycles automatically.
Taq polymerase makes a relatively high number of errors when copying DNA. Other polymerases that are stable at high temperatures have lower error rates, but Taq is still the most widely used because of its reliability and versatility, according to Colorado State University.
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