Biology 304, Molecular Biology
The Polymerase Chain Reaction
The polymerase chain reaction is a method allowing multiple copies of a specific DNA strand to be made. This method requires a double stranded DNA template, a DNA polymerase, nucleotides, and primers (Campbell, 1996).
The DNA to be amplified is heated to 90-95 degrees Celsius for thirty seconds. The two strands are thereby denatured (pulled apart). Primers are then added to the mixture which allow DNA synthesis to begin. The mixture is cooled to fifty to fifty five degrees Celsius so that the primers may anneal to the separated DNA strands and polymerization may begin (National Center for Human Genome Research, 1998).
Taq DNA polymerase, isolated from Thermus Aquaticus, bacteria which live in hot springs, is required for the polymerization step. The enzyme has highest activity at 75 degrees Celsius, so the reaction is then reheated (National Center for Human Genome Research, 1998). The Taq polymerase binds to the 3' OH groups and each of the initial strands is used as a template to create complementary strands of DNA. In this manner, the quantity of DNA is doubled.
The cycle is typically repeated about thirty times, creating
up to one billion molecules (The National Center for Human Genome Research,
1998). The vast numbers of these molecules make it easier to look for a
target sequence of DNA. It allows researchers to multiply one specific
sequence of DNA.
Figure found at URL server http://www-biology.ucsd.edu/others/dsmith/classses/pcr.html
National Center for Human Genome Research, National Institutes of Health. 1998. Polymerase Chain Reaction-Xeroxing DNA. New Tools For Tomorrow's Health Resourse. <http://www.gene.com/ae/AB/IE/PCR_ Xeroxing_DNA.html> Accessed 1998 Feb 17.
Smith. Douglas W. 1996. PCR: Polymerase Chain Reaction. <http://www-biology. ucsd.edu/others/dsmith/classes/pcr.html> Accessed 1998 Feb 17.
Campbell, Neil A. Biology, Fourth Edition. New York: The Benjamin/Cummings Publishing Company, 1996. p 380.
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