Polymerase chain reaction - Wikipedia, the free encyclopedia "PCR is used to amplify a short, well-defined part of a DNA strand. This can be a single gene, or just a part of a gene. As opposed to living organisms, the PCR process can copy only short DNA fragments, usually up to 10 kb (kb stands for kilo base pairs). Certain methods can copy fragments up to 47 kb in size, which is still much less than the chromosomal DNA of a eukaryotic cell--for example, a human cell contains about three billion base pairs.

PCR, as currently practiced, requires several basic components. These components are:

* DNA template, or cDNA which contains the region of the DNA fragment to be amplified
* Two primers, which determine the beginning and end of the region to be amplified (see following section on primers)
* Taq polymerase, which copies the region to be amplified
* Deoxynucleotides-triphosphate, from which the DNA-Polymerase builds the new DNA
* Buffer, which provides a suitable chemical environment for the DNA-Polymerase

The PCR reaction is carried out in a thermal cycler. This is a machine that heats and cools the reaction tubes within it to the precise temperature required for each step of the reaction. To prevent evaporation of the reaction mixture (typically volumes between 15-100µl per tube), a heated lid is placed on top of the reaction tubes or a layer of oil is put on the surface of the reaction mixture. These machines cost more than USD 2,500 in 2004."  ¶ 11:53 PM