A third argument holds that PCR did not exist until it was made to work in an experimental system. In a matter of hours, this target sequence can be amplified a million fold. The complementary strands of a double-stranded molecule of DNA are separated by heating. Two small pieces of synthetic DNA, each complementing a specific sequence at one end of the target sequence, serve as primers. Each primer binds to its complementary sequence.
Polymerases start at each primer and copy the sequence of that strand.
Within a short time, exact replicas of the target sequence have been produced. Koshland described described PCR entirely in terms of molecular biological technique. In an account he gave to the Smithsonian Institution's Archive of Biotechnology, Kary B. Mullis defined PCR not as a specific technique , or bundle of techniques, but rather as a concept . For Mullis, PCR came into existence at the moment he conceived of it. For him, making the concept work was of secondary importance.