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Accurately describe the basic technique of PCR (Polymerase Chain Reaction) use by...

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michealm50 | Student, Undergraduate | (Level 1) Honors

Posted February 27, 2010 at 11:32 PM via web

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Accurately describe the basic technique of PCR (Polymerase Chain Reaction) use by Forensic Scientists?

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trophyhunter1 | College Teacher | (Level 3) Senior Educator

Posted March 8, 2012 at 7:21 AM (Answer #1)

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This technique was developed by Kary Mullis, in 1983 and allows for the amplification of a single or a few copies of DNA to as many as thousands or millions of copies. It is used for DNA cloning, to study the relationships among various organisms, to diagnose hereditary diseases, to determine paternity and for in the case of forensics, to identify genetic fingerprints. PCR uses a heat-stable DNA polymerase, usually Taq polymerase. This is an enzyme that assembles a new DNA strand from nucleotides using a single stranded DNA as the template. Either strand of the DNA double helix can serve as the template.  DNA primers are used to initiate DNA synthesis. Heating and cooling is used on the PCR sample to separate the DNA double helix during DNA melting. At the lower temperature, each of the two separated strands can serve as the template in DNA synthesis using the DNA polymerase. Primers are used that are complementary to the DNA region being selected for the amplification process. Virtually it is a chain reaction because you can continually copy the DNA, and make more copies from the copies being generated. At every cycle, the amount of product is doubled, and this is considered exponential amplification.

PCR or Polymerase Chain reaction is used in forensic science to identify genetic fingerprints. If a piece of DNA is found for example at a crime scene, it can be amplified by this technique and copied many times to be used as evidence in a case. An enzyme called DNA polymerase which is heat stable, is used to assemble a new DNA strand from DNA nucleotides, using a single-stranded DNA as a template. DNA primers are required to initiate DNA synthesis. Heat is needed to separate the two DNA strands from the DNA you are trying to copy. This stage is the DNA melting step. It is also called denaturation.  Then, each strand can be used as a template to create more copies of the DNA using the DNA polymerase enzyme. The DNA template contains a specific region to be amplified. Two primers complementary to the 3 prime ends of each of the sense and anti-sense strands are needed. The DNA polymerase stage is next, which along with free nucleotides(building blocks of DNA) this enzyme can assemble a new complementary DNA strand. Buffer solution maintains the proper ph for this reaction to occur. At every cycle of the PCR process, doubling of the DNA occurs, therefore, it can be amplified exponentially and only a small quantity of DNA is needed. In forensics, a person can be identified genetically by this method therefore, any DNA left at a crime scene can be compared to different suspects to try to connect someone to a particular crime.

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