PCR

PCR, the polymerase chain reaction, synthesises many copies of a gene or DNA of interest in vitro.

It uses two sets of primers and the enzyme DNA polymerase. Primers are short, chemically synthesised oligonucleotides complementary to regions of the DNA.

Each cycle has three steps: denaturation of the double-stranded DNA, annealing of the primers, and extension of the primers.

The polymerase extends the primers, using the nucleotides supplied and the genomic DNA as the template.

Repeated many times, the process amplifies the DNA segment about a billion times, giving roughly 1 billion copies.

Repeated cycles are possible because the DNA polymerase is thermostable. It is isolated from the bacterium Thermus aquaticus and stays active through the high temperature used to denature the DNA.

The amplified fragment can then be ligated into a vector for further cloning.