ABSTRACT
Principles of PCR The polymerase chain reaction (PCR) is an extremely simple yet immensely powerful technique. It allows enormous amplification of any specific sequence of DNA provided short sequences either side of it are known. The technique is shown in Figure 1. A PCR reaction contains the target double-stranded DNA, two primers that hybridize to flanking sequences on opposing strands of the target, all four deoxyribonucleoside triphosphates and a DNA polymerase. Because, as we shall see, the reaction periodically becomes heated to high temperature, PCR depends upon using a heat-stable DNA polymerase. Many such heat-stable enzymes from thermophilic bacteria (bacteria that live in hightemperature surroundings) are now available commercially. The first one used was Taq polymerase from the thermophilic bacterium Thermus aquaticus.
