Polymerase Chain Reaction is a technique in which any genetic
sequence can be quickly amplified. The starting material for PCR is a solution
of double stranded DNA containing the nucleotide sequence that is targeted
for copying. It is important to know the DNA sequence of the interested
gene.
The enzyme DNA polymerase, which catalyses the reaction, is then added
together with nucleotides and primers. The primers determine the DNA sequence
to be amplified. The DNA strand is denatured (separated) when heated to
a certain temperature, and this allows the primers to bind to a single
stranded DNA.
Within a short time the amount of target DNA sequence has been doubled.
By repeating this cycle, we can generate an unlimited number of copies
of the DNA sequence.
Examples in the use of polymerase chain reaction:
a. A patient has a severe posterior uveitis. The clinician is concerned
about
acute retina necrosis caused by herpes simplex.
The vitreous fluid can
be aspirated and sent for PCR detection of herpes
simplex.
b. A contact lens wearer has an indolent ulcer and repeated culture
has
been negative for Acanthoamoeba. The scrapped tissue
can be sent for
PCR to look for any evidence of Acanthoamoeba.