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PCR: Polymerase chain reaction

PCR is used to generate millions of copies of a particular DNA sequence. Watch the key steps of PCR in this presentation prepared by science, mathematics, and technology teacher fellow Peta Poletti.


The polymerase chain reaction, or PCR, is used to make multiple copies of a piece of DNA.

Everything happens inside a special machine. A solution containing the DNA is placed in the machine.

The first thing that happens is that the temperature is increased to about 90 degrees. This causes the two strands in the DNA double helix to come apart, or denature.

In the second step, the temperature of the solution is lowered. This causes the primers to attach, or anneal, to the DNA.

Primers are pieces of RNA that match specific pieces of DNA. They are needed to start the process of making new DNA.

The third step requires an enzyme called Taq polymerase. This enzyme is used to make new DNA. The temperature is again increased, and the enzymes make new DNA to match the DNA strands that were separated.

The cycle is then repeated many times. The temperature is increased, and the DNA strands separate, the primers bind and the enzymes make new DNA chains.

Then it starts again – the DNA chains are separated, the primers bind, new DNA chains are made and so on.

After only 20 cycles, you have over a million copies of the original DNA.


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