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Helicase

PCR

The polymerase chain reaction copies a chosen stretch of DNA millions to billions of times.Source: NHGRISource: Saiki et al., 1988

Step 2 of 7ReadingTechnology or method

How it works

PCR is a DNA photocopier. It makes millions of copies of one small piece of DNA so there is enough to study.

Each cycle heats the DNA to separate the strands, cools it so short primers can bind on either side of the target, then lets a heat-stable polymerase copy each strand. Every cycle can roughly double the target.

Amplification is exponential while reagents last: after n cycles at efficiency E, copies grow about as (1 + E)^n. Quantitative PCR tracks this in real time; reactions eventually plateau as primers and nucleotides run out.

Used for
  • Diagnostic tests
  • Forensic DNA profiling
  • Research in genetics and evolution

Safety and ethics

Sensitive testing raises questions about consent and privacy when samples come from people.
See it in the Biotechnology lab

How PCR connects

PCR uses

  • Process

    DNA replication

    Copying DNA before a cell divides. Each new double helix keeps one original strand and gains one new strand.

  • Organism or group

    Thermophiles

    Microbes that thrive in heat, such as Thermus aquaticus from hot springs, the source of a heat-stable enzyme used in PCR.

    Open in Microbe Lab

Explore further

Open in Biotech LabIn the knowledge graphFind papers about PCR

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Next: DNA sequencing

Sources & further reading

The explanations on this page are our own summaries of these sources. Follow a link to read the original; if anything here disagrees with it, the original wins. How we choose and check sources.