Polymerase chain reaction

The polymerase chain reaction (PCR) is a laboratory method widely used to amplify copies of specific <a href="/facts/DNA/nB89Iauz">DNA</a> sequences rapidly, to enable detailed study. PCR was invented in 1983 by American <a href="/facts/Biochemist/gAWNAY5v">biochemist</a> <a href="/facts/Kary_Mullis/Ad33QwQe">Kary Mullis</a> at <a href="/facts/Cetus_Corporation/Fr0keNBj">Cetus Corporation</a>. Mullis and biochemist <a href="/facts/Michael_Smith_(chemist)/UGxtgVjX">Michael Smith</a>, who had developed other essential ways of manipulating DNA, were jointly awarded the <a href="/facts/Nobel_Prize_in_Chemistry/8Nb8Ajjy">Nobel Prize in Chemistry</a> in 1993.
PCR is fundamental to many of the procedures used in <a href="/facts/Genetic_testing/H21wH0ze">genetic testing</a>, research, including analysis of <a href="/facts/Ancient_DNA/CVKj1QhD">ancient samples of DNA</a> and identification of infectious agents. Using PCR, copies of very small amounts of <a href="/facts/DNA_sequences/qAf4kTee">DNA sequences</a> are exponentially amplified in a series of cycles of temperature changes. PCR is now a common and often indispensable technique used in <a href="/facts/Medical_laboratory/ov10GjQD">medical laboratory</a> research for a broad variety of applications including <a href="/facts/Biomedical_research/lSVBFxDJ">biomedical research</a> and <a href="/facts/Forensic_science/4upVa2vB">forensic science</a>.
The majority of PCR methods rely on <a href="/facts/Thermal_cycler/9Y3ep6j4">thermal cycling</a>. Thermal cycling exposes reagents to repeated cycles of heating and cooling to permit different temperature-dependent reactions—specifically, <a href="/facts/DNA_melting/4YD7V7hM">DNA melting</a> and <a href="/facts/Enzyme/DSI1Fh7y">enzyme</a>-driven <a href="/facts/DNA_replication/wrU6RuR3">DNA replication</a>. PCR employs two main reagents—<a href="/facts/Primer_(molecular_biology)/I3fBfwte">primers</a> (which are short single strand DNA fragments known as <a href="/facts/Oligonucleotide/Gc99fPnC">oligonucleotides</a> that are a <a href="/facts/Complementary_DNA/P2nWeY4T">complementary</a> sequence to the target DNA region) and a <a href="/facts/Thermostable_DNA_polymerase/2NGGusco">thermostable DNA polymerase</a>. In the first step of PCR, the two strands of the DNA double helix are physically separated at a high temperature in a process called <a href="/facts/Denaturation_(biochemistry)/Eh1hc3Bg">nucleic acid denaturation</a>. In the second step, the temperature is lowered and the primers bind to the complementary sequences of DNA. The two DNA strands then become <a href="/facts/DNA/nB89Iauz">templates</a> for DNA polymerase to <a href="/facts/Enzyme/DSI1Fh7y">enzymatically</a> assemble a new DNA strand from free <a href="/facts/Nucleotide/pQKEwlJI">nucleotides</a>, the building blocks of DNA. As PCR progresses, the DNA generated is itself used as a template for replication, setting in motion a <a href="/facts/Chain_reaction/5UwHTKXS">chain reaction</a> in which the original DNA template is <a href="/facts/Exponential_growth/m4yEqKJ7">exponentially</a> amplified.
Almost all PCR applications employ a <a href="/facts/Thermostable_DNA_polymerase/2NGGusco">heat-stable DNA polymerase</a>, such as <a href="/facts/Taq_polymerase/ElSRbPss">Taq polymerase</a>, an enzyme originally isolated from the <a href="/facts/Thermophile/HGuP161d">thermophilic</a> bacterium <a href="/facts/Thermus_aquaticus/AUvSjc6U">Thermus aquaticus</a>. If the polymerase used was heat-susceptible, it would denature under the high temperatures of the denaturation step. Before the use of Taq polymerase, DNA polymerase had to be manually added every cycle, which was a tedious and costly process.
Applications of the technique include <a href="/facts/DNA_cloning/Te56373e">DNA cloning</a> for <a href="/facts/DNA_sequencing/hsPsNCQW">sequencing</a>, gene cloning and manipulation, gene mutagenesis; construction of DNA-based <a href="/facts/Phylogeny/f5vVEpeY">phylogenies</a>, or functional analysis of <a href="/facts/Gene/e1swwPY6">genes</a>; <a href="/facts/Medical_diagnosis/J47rvb0p">diagnosis</a> and <a href="/facts/Monitoring_(medicine)/cTc3d1j5">monitoring</a> of <a href="/facts/Genetic_disorder/hFqt2NLn">genetic disorders</a>; amplification of ancient DNA; analysis of genetic fingerprints for <a href="/facts/DNA_profiling/NhYPDDH4">DNA profiling</a> (for example, in <a href="/facts/Forensic_science/4upVa2vB">forensic science</a> and <a href="/facts/Parentage_testing/1d1tGXGa">parentage testing</a>); and detection of <a href="/facts/Pathogen/axMXtV1M">pathogens</a> in <a href="/facts/Nucleic_acid_test/mqXky9Ej">nucleic acid tests</a> for the diagnosis of <a href="/facts/Infectious_disease/182XrncP">infectious diseases</a>.

Polymerase chain reaction open-in-new

Polymerase chain reaction