From the article This Time, It’s Personal.
The 1993 Nobel Prize for chemistry recognized Kary Mullis for the invention of PCR because the technique has revolutionized medicine, forensics, biology and biochemistry. Since then, variations of PCR have emerged that have broadened its application – for example, real-time qPCR for measuring DNA and reverse transcription real-time qPCR for quantifying RNA.
Now that the human genome has been sequenced, scientists are thinking big when it comes to DNA and RNA. Demand has increased for faster, less expensive PCR that can quantify multiple RNA and DNA molecules at once.
Essentially, PCR mimics DNA replication as it occurs in the cell. Short sequences of DNA called primers are mixed in test tubes along with the DNA sequence of interest and DNA polymerase, an enzyme that copies the DNA sequence of interest and thus produces more of it. The DNA polymerase comes from a heat-tolerant organism, usually from Thermus aquaticus (Taq). The mixture in the test tubes is kept at a certain temperature at which the polymerase and primers can bind to the template DNA; then the mixture is heated so that the primers and polymerase separate from the strand. Next the temperature is lowered to allow the polymerase and primers to bind again for another round. The process is repeated many times to make a lot of DNA. In quantitative PCR, fluorescent probes are used to quantify exactly how much DNA is there to begin with
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