Lab & analytical techniques · Reference
What is PCR as a laboratory technique?
PCR is a laboratory technique that amplifies a chosen DNA sequence by repeated thermal cycling, doubling the target with each cycle so a tiny amount of DNA becomes millions of copies.
How the thermal cycling works
PCR is driven by repeated changes in temperature, carried out automatically in a thermal cycler. Each cycle has three steps: denaturation at around 95 °C separates the two DNA strands; annealing at a lower temperature lets short primers bind the sequence flanking the target; and extension at around 72 °C lets a heat-stable DNA polymerase build new complementary strands from free nucleotides. Repeating the cycle roughly doubles the number of target copies each time, giving exponential amplification. This biochemistry is explained in more depth at PCR in molecular biology.
Invention and key components
The polymerase chain reaction was conceived by Kary Mullis in 1983, work for which he shared the 1993 Nobel Prize in Chemistry. Its practicality came from using a heat-stable polymerase (Taq) that survives the high denaturation temperature, removing the need to add fresh enzyme each cycle.
A reaction needs the template DNA, a pair of primers defining the target, the four nucleotides, the polymerase, and a buffer with magnesium ions. The primer sequences determine exactly which region is amplified.
Variants and uses in research
Variations extend the basic method: quantitative PCR (qPCR) monitors amplification in real time to measure starting DNA amount, while reverse-transcription PCR (RT-PCR) first converts RNA to DNA so RNA can be amplified. As an instrument-based technique, PCR underpins cloning, sequencing preparation, genotyping, and the detection of specific sequences in research and forensic laboratories. Products are commonly checked by gel electrophoresis.
Key facts
At a glance
- Full name: polymerase chain reaction
- Invented by: Kary Mullis, 1983 (Nobel Prize 1993)
- Instrument: a thermal cycler
- Three steps per cycle: denaturation, annealing, extension
- Key enzyme: heat-stable polymerase (e.g. Taq)
- Growth: roughly doubles the target each cycle
Common questions
FAQ
How does PCR amplify DNA?+
PCR cycles a reaction through denaturation, primer annealing, and extension. A heat-stable polymerase copies the target sequence each cycle, and because each cycle roughly doubles the number of copies, the target grows exponentially.
Who invented PCR?+
PCR was invented by Kary Mullis in 1983, and he shared the 1993 Nobel Prize in Chemistry for it. The use of a heat-stable polymerase such as Taq made the technique practical to automate.
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