Polymerase chain reaction was invented by Kary Mullis. He was awarded the Nobel Prize in Chemistry in 1993 for his invention, only seven years after he and his colleagues at Cetus first reduced his proposal to practice.
During PCR a selected target sequence of DNA or RNA (reverse transcriptase PCR) is amplified. In the annealing step primers (20-30 bp oligonucleotides) complementary to a conserved region at the beginning of the template create the short piece of double stranded DNA for the polymerase (heat stable enzyme for amplification) to start amplification. PCR is a cycling reaction. Each cycle has three components: Denaturation at high temperature (about 94°C, separates double-stranded DNA into single strands); Annealing (50-65°C to allow primers to hybridize/anneal to target DNA sites); replication/elongation (72°C DNA polymerase binds and makes DNA) (see figure).
Because the products of each PCR cycle can act as templates for the next PCR cycle, the number of new identical molecules produce doubles with each repetition of the cycle leading to exponential amplification.
Click on image to enlarge
