Life sciences · Reference
What is PCR (polymerase chain reaction)?
PCR is a laboratory method that rapidly makes millions of copies of a specific DNA sequence, allowing researchers to amplify a tiny amount of DNA into quantities large enough to study.
Amplifying DNA
PCR solves a basic problem: many experiments need more copies of a specific DNA sequence than a sample naturally provides. PCR amplifies a chosen region, defined by short DNA primers, doubling the number of copies with each cycle so that even a few molecules become billions. Because the copying is exponential, PCR can take a vanishingly small amount of starting DNA and produce enough to detect, sequence, or manipulate.
The three steps of a cycle
Each PCR cycle has three temperature-controlled steps. In denaturation, heat separates the two DNA strands. In annealing, the temperature is lowered so that short primers bind to their matching sequences flanking the target.
In extension, a DNA polymerase extends from the primers to synthesise new complementary strands. Repeating this cycle many times — typically using an automated thermal cycler — multiplies the target sequence exponentially.
Taq polymerase and the thermal cycler
A key enabling component is a heat-stable DNA polymerase, classically Taq polymerase from a thermophilic bacterium, which survives the repeated high temperatures of denaturation. The reactions are run in a thermal cycler, an instrument that automatically shifts the sample through the precise temperatures of each step, making PCR fast, reliable, and easy to repeat.
History and research use
PCR was conceived by Kary Mullis in 1983, work for which he shared the 1993 Nobel Prize in Chemistry. It has become one of the most important techniques in molecular biology, used in research for cloning, sequencing preparation, detecting specific sequences, and much more. For the instrument-and-protocol details, see the laboratory-techniques companion page at /lab-techniques/pcr; this page focuses on the definition and core concept of PCR.
Key facts
At a glance
- Full name: polymerase chain reaction
- Purpose: amplify a specific DNA sequence
- Invented by: Kary Mullis, 1983
- Nobel Prize in Chemistry: Mullis, 1993
- Three steps: denaturation, annealing, extension
- Key enzyme: a heat-stable DNA polymerase (e.g. Taq)
Common questions
FAQ
What does PCR do?+
PCR makes many copies of a specific DNA sequence. Through repeated cycles of denaturation, annealing, and extension, it amplifies a small starting amount of DNA into millions or billions of copies for study.
Who invented PCR?+
PCR was invented by Kary Mullis in 1983. He shared the 1993 Nobel Prize in Chemistry for developing the method.
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