DNA/PCR

How does the test work?

The Polymerase Chain Reaction (PCR), is the technique used to detect small amounts of DNA and make enough copies of it to be detectable.

All cells, bacteria and viruses contain DNA or RNA that is unique to them. When a sample arrives for testing it is prepared by a lengthy digestion and purification process to release all DNA from that sample.

The prepared sample is then added to a PCR mixture containing small pieces of DNA (primers) which match the DNA we are testing for, building blocks of DNA, and a polymerase enzyme which can join the blocks together to make copies of DNA.

If there is DNA that we are testing for in the sample, the matching primers will stick to the DNA, and the polymerase will start making copies of the DNA. Each copy of DNA can then bind the matching primers and another two copies can be made. This chain reaction is repeated up to forty times, resulting in a comparatively huge amount of DNA at the end of the cycle generated from the little that was originally present.

If the sample does not contain the DNA we are testing for, there is nothing for the primers to stick to and the polymerase will not make any DNA.

When the PCR is finished, the samples are run through a gel matrix and put under a UV light. Any DNA present will glow in a bright band which indicates that the sample is positive for the DNA we are testing for.