PCR
BY Shelby, Alex, and Patrick
Polymerase chain reaction is a scientific technique that amplifies a single or a
few copies of a piece of DNA, creating many copies of a particular DNA sequence. In
order for this to occur thermal cycling is needed. Which is the repetitive heating and
cooling of the RXN for DNA melting and enzymatic replication of DNA.
Primers and DNA polymerase are important for selective and repeated
amplification. WHEN PCR progresses the DNA it generates is used for replication
making a chain reaction where the DNA template is greatly amplified. It then makes a
new DNA strand from nucleotides by using DNA primers and a single-stranded DNA as
a template, which starts the sequence.
Thermal cycling is put into to steps so it can physically divide two strands of the
double helix of a DNA through the process of DNA. Once at a lower temp. each strand is
used as a template for DNA synthesis by DNA polymerase. DNA polymerase selects the
strands by using primers that go along with a DNA region that’s been targeted by thermal
cycling
PCR can be manipulated for many different genetic purposes. Most PCR
applications need heat-stable DNA polymerase an example is taq polymerase.
PCR is necessary in cloning, since it is a cheap and effective method, but also
allows us to locate rare / hard to locate sequences. In environmental PCR, the method can
be used to amplify organisms found in nature samples and show us what is there. One
may also learn how different types of organisms affect the rate of PCR, and to compare
these different types based on their composition (i.e. invertebrate vs. vertebrate)
Summarized steps of PCR
Denaturation: Sample of DNA is heated, separating the double helix into two separate
strands of DNA.
Annealing: Temperature in the sample is decreased, allowing primers to bond to each
strand, with new bases forming on each. Once bases are set and strong, the template is
able to be fulfilled back into a double helix.
Extension: Temperature is increased to ideal temperature for ideal replication for the
primer to work in. Two strands of DNA are made instead of the natural number of one.
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http://users.ugent.be/~avierstr/principles/pcr.html
INTRESTING ARTICLE
In Guangdong, China, SARS (Severe Acute Respiration Syndrome) emerged as a disease
caused by the SARS coronavirus, which leads to severe trouble with breathing, and has
the potential to cause death. SARS disease is very contagious, and was spread through
travel from Guangdong. PCR is used as a method to test for the presence of SARS in
people, and is found to be one of the easiest and most effective methods. PCR is able to
replicate the desired strand of DNA, namely SARS in this situation, and not replicate
strands that are undesirable. By repeating this replication process, SARS will either be
located, or not (if not present). This method is very accurate and “sensitive” to DNA
present, and results are usually distorted due to laboratory failure or contamination of the
sample of DNA.
Works Cited
1. Phillips, By Theresa. "Polymerase Chain Reaction - PCR - How Pcr Works."
Biotechnology - Biomedical - Biotech. Web. 10 Dec. 2010.
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2. "WHO | Use of Laboratory Methods for SARS Diagnosis." Web. 10 Dec. 2010.
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3. "Principle of the PCR." Web. 10 Dec. 2010.
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