DNA is the molecule which carries all
our inherited information. It has a double helix structure, and
is made up of four nucleotide bases – adenine, thymine, cytosine
and guanine - joined together in pairs. Since the structure and
importance of DNA was first recognised over fifty years ago the
molecule has been studied by thousands of scientists. One development
which has made it much easier for everyone else working in the field
is the Polymerase Chain Reaction (PCR).
PCR has revolutionised molecular biology and DNA technology. Invented
by Kary B Mullis, it enables the production of large quantities
of DNA from very small samples in a remarkably short time. This
in turn makes it possible to analyse tiny samples of DNA and unravel
the mysteries of individual genes.
Every time a cell in the body reproduces itself, the DNA in the
nucleus is copied. The double helix of the DNA ‘unzips’,
and the enzyme DNA polymerase makes a copy using the separated strands
as templates. For the process to work there must be plenty of nucleotide
bases, the small primer sequences which are needed to get the copying
process started and the enzyme DNA polymerase.
 In
1983 Kary Mullis came up with the idea of using enzymes from
a bacterium which lives in the hot springs in Yellowstone National
Park to develop a technique for replicating DNA artificially in
the lab. His idea worked, and he was awarded the Nobel prize for
chemistry in 1993.
How does PCR work?
The polymerase chain reaction depends on the fact that the different
stages of DNA replication using enzymes from Thermus aquaticus
take place at different temperatures. So by mixing all the ingredients
together at the beginning and then changing the temperature of the
mixture in the PCR machine a tiny amount of DNA can be amplified
to produce millions of identical molecules.
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