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. You will be able to make a wise decision.
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