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What is PCR (Polymerase Chain Reaction)?

posted by DNA Identifiers @ 10:10 AM
Friday, April 9, 2010

By Grant Kretzer

One of the issues that scientists commonly encounter when they are processing a DNA test is that they don’t have enough DNA to work with. By using a method called polymerase chain reaction (PCR), scientists can take a single copy of a piece of DNA and multiply it consistently until they have millions, if not more, copies of the DNA piece to work with.  Many times scientists are given just a few strands of DNA to work with, this can prove challenging when trying to obtain a sample. The main problem is that sometimes, more abundant DNA is required for testing purposes to produce accurate results. Often, a scientist is looking for thousands, if not millions, of different chains of the DNA in question so that they can continuously run tests on in order to produce accurate results.

The name polymerase chain reaction (PCR) comes from the key component in the amplification of DNA.  DNA polymerase is an enzyme that assists in the replication of DNA. They catalyze (speed up) the polymerization of deoxyribonucleotides alongside the DNA strand. These polymerases read the code and then use it as a template. By using it as a template, they are able to make another strand and then another strand, to create the required quantity of material for examination.

DNA Testing – Development of the PCR technique

The PCR technique was developed in 1983 by Karry Mullis. Karry Mullis shared the 1993 Nobel Prize in Chemistry with Michael Smith. Mullis received the prize for his development of the Polymerase Chain Reaction (PCR), a process first described by Kjell Kleppe and 1968 Nobel laureate H. Gobind Khorana that allows the amplification of specific DNA sequences.  The improvements provided by Mullis have made PCR a central technique in biochemistry and molecular biology. The story behind its invention is rather interesting. The inspiration for PCR came from road markings, according to Mullis, he was driving his vehicle late one night with his girlfriend, who was also a chemist, when he had the idea to use a pair of primers to bracket the desired DNA sequence and to copy it using DNA polymerase, a technique which would allow a small strand of DNA to be copied almost an infinite number of times.

DNA Testing – Key application of PCR

One particular field of science that relies heavily on PCR is DNA forensic testing. If hair was left at a crime scene that was not that of the victim, scientists would have little material to work with. If they want to run one of the many different types of DNA testing, they will naturally require more DNA to analyze. Therefore, by running a polymerase chain reaction, they can replicate more of the DNA for testing purposes. By doing this, they can ensure that they have enough to continuously run DNA tests, with a view to providing more accurate results.

The creation of the polymerase chain reaction was a defining improvement to molecular biology and biochemistry. At one time, scientists were only able to use very little amounts of the desired DNA chain, yet now they are able to replicate the sequence they desire and continuously create more and more material for testing purposes, which is of particular relevance in forensic testing of genetic material or in determining whether an accused individual may in fact be guilty of the alleged crime.

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2 Responses to “What is PCR (Polymerase Chain Reaction)?”

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