Many Applications from a Simple Idea
April, 1983, Kary Mullis took a drive on a moonlit California mountain
road and changed the course of molecular biology. During that drive, he
conceived the Polymerase Chain Reaction (PCR).
is an in vitro
method for enzymatically synthesizing defined sequences of DNA
(Figure 1). The reaction uses two oligonucleotide primers that hybridize
to opposite strands and flank the target DNA sequence that is to be
amplified. The elongation of the primers is catalyzed by a heat-stable
DNA polymerase (such as Taq DNA Polymerase)1.
ends of the fragment are defined by the 5' ends of the primers2.
Because the primer extension products synthesized in a given cycle can
serve as a template in the next cycle, the number of target DNA copies
approximately doubles every cycle; thus, 20 cycles of PCR yield about a
million copies (220) of the target DNA.
The PCR technique is now so pervasive in molecular biology that it is difficult to think of life without it. Because of PCR, “insufficient nucleic acid” is no longer a limitation in molecular biology research and many medical diagnostic procedures. More importantly, innovative researchers have continually updated the definition of “PCR applications”, increasing the usefulness and scope of the technique.