PCR And Its Use


Often times, scientists only have a small amount of DNA to deal with when doing
genetic research or studies. In these situations, scientists can do one of
several things. One is to just try to work with it anyway, but this is nearly
impossible (depending on how much there is). Ther are a couple other processes
they can use, or they can use PCR. PCR is one of the more complicated, but
reliable ways to do tests on DNA when they only have a small amount to begin
with. PCR, or Polymearse Chain Reaction, is the scientific process used by
genetic scientists to clone DNA.

"A \'rapid diagnostic\' technique used in the clinical microbiology lab to detect
pathogens. It relies upon amplification technology utilizingthe heat stable DNA
polymerase from a thermophilic organism." (from
http://www.genes.com/pcr/pcrinfo.html) Dr. K.Mullis recently received the Nobel
prize for inventing the technique.

This is how they go about doing this: They first get their small DNA sample.
Then they mix all the chemicals (this includes the primer, etc). Then they have
to run it through the PCR machine. Here is a (rather detailed) description of
the process: "The cycling protocol consisted of 25-30 cycles of three-
temperatures: strand denaturation at 95degC, primer annealing at 55degC, and
primer extension at 72deg C, typically 30 seconds, 30 seconds, and 60 seconds
for the DNA Thermal Cycler and 4 seconds, 10 seconds, and 60 seconds for the
Thermal Cycler 9600, respectively."

Basically, that means that they set it to certain temperatures, then put it in
different cyles for different amounts of time. PCR machines can be compared
with washing machines. There are the different temperatures (here for example,
there is 72degC, where in the washing machine you would set it to cold/cold
respectively.

For it to properly replicate, we must know how to match each of the following:

A T G A T A T G G C A G C A A C G A C C A T A

the match would be

T A C T A T A C C G T C C T T G C T G T A T

The whole process is pretty much summed up like this: They heat up the DNA to
let the enzymes break it down (or \'unzip\' its bonds). Then add specific amounts
of the primer (relative to the amount of DNA you have. Then you add the enzyme
to sets of 4 nuclotides that will go through the genetic sequence of nucleotides
and hook up the matching nucleotide (A goes to T and G to C etc). Keep adding 4
more after the enzymes finish with the one you just added it to.

When all this is done, there will no longer be a shortage of DNA, but an
abundant amount, so the tests can be properly run on it. PCR isn\'t as difficult
to understand as it may seem at first, but it can be explained in a very simple
way:

C = Cytosine G = Guanine A = Adenine T = Thymine

You will now assume the role of a genetic scientist. Here is the little bit of
DNA that you have managed to obtain:

C G A T T A T G A G C C G A G

The PCR process will perform an artificial \'protein synthesis\' in a way. It
(through heat) will break down the bonds that currently keep your specimin in
tact. It will, basically, just line up the nucleotides with their match, and
the two strands of the double helix will become two full strands of DNA. So,
the above code is the coding for one strand of your DNA sample. The PCR machine,
will in effect, match them up:

G C T A A T A C T C G G A T C

PCR has many uses. It can be used in criminal cases, when they only have a
fragment of a speck of blood to deal with. They can also use it to piece back
together the DNA of an ancient fossil of a dinosaur. The possibilites just
never seem to end with DNA. Until recently, there was no such thing as the PCR
or a PCR machine. You had to do things by hand and that really added to the
cost of research. In effect, not as many people heard about what was going on
in the world of DNA. People should be educated about DNA because if you know
about DNA it can be useful if you are ever called to jury duty and they are
using that kind of evidence.