PCR stands for Polymerase Chain Reaction. In this reaction, multiple copies of the gene (or DNA) of interest is synthesised in vitro using two sets of primers (small chemically synthesised oligonucleotides that are complementary to the regions of DNA) and the enzyme DNA polymerase.
Each cycle of Polymerase chain reaction (PCR) has three steps: (i) Denaturation; (ii) Primer annealing; and (iii) Extension of primers.
(i) Denaturation, in which double-stranded DNA templates are heated to separate the strands.
(ii) Annealing, in which short DNA molecules called primers bind to flanking regions of the target DNA.
(ii) Extension, in which DNA polymerase extends the 3′ end of each primer along the template strands. These steps are repeated (“cycled”) 25–35 times to exponentially produce exact copies of the target DNA.