PCR stands for polymerase chain reaction. In this reaction, multiple
copies of the gene of interest are synthesized in vitro under three
steps.
(i) Denaturation : In this, double stranded DNA is converted
to the single stranded often achieved by heating or alkaline conditions.
This is called "melting" of DNA.
(ii) Annealing : The two sets of
primers (small chemical synthesized oligonucleotides that are
complementary to the regions of DNA) undergo biochemical process of
annealing at an optimum temperature of 40−650C.
Extension: The
enzyme DNA polymerase extends the primers using the nucleotides provided
in the reaction and the genomic DNA as template.
In the process of
replication of DNA is repeated many times, the segment of DNA can be
amplified to approximately billion times. Such repeated amplification is
achieved by the use of a thermostable DNA polymerase and the amplified
fragment if desired can be used to ligate with a vector for further
cloning.