Polymerase Chain Reaction
has been called by some the greatest achievement of
modern molecular biology, Kary B. Mullis developed the polymerase chain reaction (PCR) in 1983. PCR allows the
rapid synthesis of designated fragments of DNA. Using the technique, over one
billion copies can be synthesized in a matter of hours.
One cycle of the PCR process, which consists of three main steps, takes under two minutes. In the first step, called denaturation, the DNA, stored in a vial, is heated for thirty seconds at a temperature of about 90 degrees Celsius. This heating breaks apart the two strands of the DNA molecule. The temperature is lowered to 55 degrees Celsius for the next twenty seconds. During this period, called annealing, oligonucleotide primers bond to the individual strands of DNA. The oligonucleotide primers serve to initiate DNA replication. The temperature of the solution is raised to 75 degrees Celsius during the polymerization period, in which an enzyme called polymerase replicates the strands of DNA. Thirty iterations of this process will create over one billion copies of an original DNA segment.
PCR is valuable to scientists by assisting gene mapping, the study of gene functions, cell identification, and to forensic scientists in criminal identification. Cetus Corporation, Mullis' employer at the time of his discovery, was the first to commercialize the PCR process. In 1991, Cetus sold the PCR patent to Hoffman-La Roche for a price of $300 million. It is currently an indispensable tool for molecular biologists and the development genetic engineering.