Biomedical Engineering Reference
In-Depth Information
How Does PCR Work?
The DNA isolated from cells, or from another source, is combined with primers and with
DNA polymerase , a protein that copies the DNA between the primers. The trick is to use
a DNA polymerase that can withstand high temperatures. Taq polymerase, widely used in
PCR, was isolated from a bacterium, Thermos aquaticus , discovered growing in a hot
spring. With 20 to 30 repeated cycles of heating to separate the strands of DNA, and then
cooling to allow the primers to bind and the DNA polymerase to copy the region between
the primers again, enough DNA for analysis is made from the sample. Twenty-three
cycles will generate 2,097,152 copies of the original sequence (Figure 1.3).
This ground-breaking technique for making multiple copies of DNA in a test tube was
invented in the 1980s by Kary Mullis, a biochemist. Mullis' revolutionary technique earned
him a Nobel Prize in Chemistry in 1993.
Figure 1.3 Polymerase chain reaction, or PCR, allows scientists to produce many exact
copies of a piece of DNA. The process is illustrated here.
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