Editing Molecular biology (section)

===Polymerase chain reaction===
{{main|Polymerase chain reaction}}

Polymerase chain reaction (PCR) is an extremely versatile technique for copying DNA. In brief, PCR allows a specific [[DNA sequencing|DNA sequence]] to be copied or modified in predetermined ways. The reaction is extremely powerful and under perfect conditions could amplify one DNA molecule to become 1.07 billion molecules in less than two hours. PCR has many applications, including the study of gene expression, the detection of pathogenic microorganisms, the detection of genetic mutations, and the introduction of mutations to DNA.<ref>{{Cite journal|last=Lenstra|first=J. A.|date=July 1995|title=The applications of the polymerase chain reaction in the life sciences|url=https://pubmed.ncbi.nlm.nih.gov/7580841/|journal=Cellular and Molecular Biology (Noisy-Le-Grand, France)|volume=41|issue=5|pages=603–614|issn=0145-5680|pmid=7580841}}</ref> The PCR technique can be used to introduce [[Restriction site|restriction enzyme sites]] to ends of DNA molecules, or to mutate particular bases of DNA, the latter is a method referred to as [[site-directed mutagenesis]]. PCR can also be used to determine whether a particular DNA fragment is found in a [[cDNA library]]. PCR has many variations, like reverse transcription PCR ([[RT-PCR]]) for amplification of RNA, and, more recently, [[quantitative PCR]] which allow for quantitative measurement of DNA or RNA molecules.<ref>{{cite web|title=Polymerase Chain Reaction (PCR)|url=https://www.ncbi.nlm.nih.gov/probe/docs/techpcr/| work = National Center for Biotechnology Information | publisher = U.S. National Library of Medicine |access-date=31 December 2016}}</ref><ref>{{cite web|title=Polymerase Chain Reaction (PCR) Fact Sheet|url=https://www.genome.gov/10000207/polymerase-chain-reaction-pcr-fact-sheet/|website=National Human Genome Research Institute (NHGRI)|access-date=31 December 2016}}</ref>[[File:Two percent Agarose Gel in Borate Buffer cast in a Gel Tray (Front, angled).jpg|thumb|Two percent [[agarose|agarose gel]] in [[Borate buffered saline|borate buffer cast]] in a gel tray]]