PCR: Uses, Steps, Purpose

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, and 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

The match would be

T A C T A T A C C

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 specimen intact.  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 C 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 possibilities 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.

William Anderson (Schoolworkhelper Editorial Team)

William completed his Bachelor of Science and Master of Arts in 2013. He current serves as a lecturer, tutor and freelance writer. In his spare time, he enjoys reading, walking his dog and parasailing. Article last reviewed: 2022 | St. Rosemary Institution © 2010-2024 | Creative Commons 4.0

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