LABORATORY
UNDERSTANDING
PCR
Remo Lobetti BVSc MMedVet (Med) PhD Dipl ECVIM (Internal Medicine)
Bryanston Veterinary Hospital
PO Box 67092, Bryanston, 2021, South Africa
Email: [email protected]
INTRODUCTION
The polymerase chain reaction (PCR) is a technique
in molecular biology that analyses short sequences of
DNA or RNA and is used in the diagnosis of a variety of
infectious and genetic diseases. PCR is used to amplify
a piece of DNA resulting a chain reaction in which the
target DNA is amplified exponentially leading to numerous
copies of that DNA, which can then be easily visualised on
an agarose gel. By use of a reverse transcriptase step, RNA
is converted to DNA and thus the technique can also be
used to detect RNA (RT-PCR).
The key to understanding PCR is that every human,
animal, plant, parasite, bacterium, or virus contains genetic
material sequences (nucleotide sequences or pieces
of DNA or RNA) that are unique to their species, and to
the individual member of that species. Thus if a sample
contains segments of DNA or RNA, PCR can amplify these
unique sequences so they can then be used to determine
with a very high probability the identity of the source (a
specific person, animal, or pathogenic organism) of the
trace DNA or RNA found in or on almost any sample of
material.
Once the amplification is done, the amplified segments
are compared to other nucleotide segments from a
known source (for example, a specific person, animal,
or pathogenic organism), which is done by placing PCR-
generated nucleotide sequences next to known nucleotide
sequences in a separating gel.
PCR IN PRACTICE
PCR can detect and identify pathogenic organisms,
especially those that are difficult to identify with other
methods; diagnose genetic diseases; and identify and
characterise genetic mutations found in certain cancers.
Issue 02 | APRIL 2017 | 21