T2+PCR+Background

**PCR Background**

 The Polymerase Chain Reaction (PCR) is a technique used to amplify single or multiple copies of a specific region of DNA in order to produce enough DNA to be adequately tested. This technique is useful to start templates for sequencing and is one of the best means to produce a large number of copies of DNA molecules from minute quantities of DNA source material.
 * What is PCR? What is its purpose? **

The original molecule or molecules of DNA are replicated by the DNA polymerase enzyme, thus doubling the number of DNA molecules. Then each of these molecules is replicated in a second "cycle" of replication, resulting in four times the number of the original molecules. Again, each of these molecules is replicated in a third cycle of replication. This process is known as a "chain reaction" in which the original DNA template is exponentially amplified.

With PCR it is possible to amplify a single piece of DNA, or a very small number of pieces of DNA, over many cycles, generating millions of copies of the original DNA molecule. PCR has been extensively modified to perform a wide array of genetic manipulations, diagnostic tests, and for many other use.

**What is PCR used for?**
 It is widely used un a range of scientific disciplines. In Microbiology and molecular biology, for example, PCR is used in research laboratories in DNA cloning procedures, Southern blotting, DNA sequencing, and recombinant DNA technology. In clinical microbiology laboratories, PCR is invaluable for the diagnosis of microbial infections and epidemiological studies. PCR is also used in forensics laboratories and is especially useful because only a tiny amount of original DNA is required, for example, sufficient DNA can be obtained fro a droplet of blood or a single hair.

**What are used during the PCR procedure?**
The following are all in the test tube: 
 * Small quantity of DNA
 * Primers
 * Buffered solution containing DNA polymerase
 * Four base pairs of DNA
 * Cofactor MgCl2

**What is the PCR procedure? **

 * <span style="font-family: Georgia,serif; font-size: 120%; line-height: 37px;">﻿There are three main stages in a PCR that are usually repeated on an average of 35 cycles on an automated cycler which can **
 * <span style="font-family: Georgia,serif; font-size: 120%;"> The Basic steps for the PCR are as the following: **
 * 1) <span style="font-family: Georgia,serif; font-size: 120%;">__**Denaturation (at 95 degrees C).**__ In this stage, the double strand melts open to single stranded DNA and all enzymatic reactions stop.
 * 2) <span style="font-family: Georgia,serif; font-size: 120%;">__**Annealing (at 45 degrees C).**__ The single stranded sample DNA from the previous step is mixed with a probe, while hydrogen bonds form between this probe and its complementary sequence in the sample DNA. Therefore, the double-helix structure is re-created.
 * 3) <span style="font-family: Georgia,serif; font-size: 120%;">__**DNA Synthesis or Extension (at 72 degrees C).**__ This is the best stage and temperature for the polymerase. In this process, the primer (a piece of DNA where its 3' end is the starting point for the new DNA) starts mDNA by attracting bases to attach to it. Primers that are on positions with no exact match get loose again and don't give an extension of the fragment.



=<span style="background-color: #800080; font-family: Georgia,serif; font-size: 120%;"> Fun Facts on PCR! =
 * <span style="font-family: Georgia,serif; font-size: 120%;"> PCR has been used to amplify DNA from: **
 * <span style="font-family: Georgia,serif; font-size: 120%;">A preserved quagga (a zebra relative that became extinct 100 years ago)
 * <span style="font-family: Georgia,serif; font-size: 120%;">Crime Scenes
 * <span style="font-family: Georgia,serif; font-size: 120%;">Eight-celled human pre-embryos, to detect cystic fibrosis
 * <span style="font-family: Georgia,serif; font-size: 120%;">The brain of a 7000 year old American mummy
 * <span style="font-family: Georgia,serif; font-size: 120%;">Patients for disease diagnosis

<span style="font-family: Georgia,serif; font-size: 180%;">__**Bibliography:**__
 * <span style="font-family: Georgia,serif; font-size: 16px; line-height: 32px;">The Woodrow Wilson Foundation Leadership Program. "Background for Polymerase Chain Reaction (PCR)." // The Woodrow Wilson National Fellowship Foundation //. 2000 Summer Biology Institute Biodiversity, 2011. Web. 27 Apr. 2011. <http://www.woodrow.org/teachers/bi/2000/Doggy_DNA/background_for_polymerase_chai.html>.
 * <span style="font-family: Georgia,serif; font-size: 16px; line-height: 15px;">discover.mbl.edu/downloads/DMW.MolecularTechniques.ppt
 * <span style="font-family: Georgia,serif; font-size: 16px; line-height: 15px;">http://www.horizonpress.com/pcr/

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