What is Polymerase Chain Reaction?

Polymerase Chain Reaction (PCR) is a microbiological technique used to make copies of DNA, allowing very small samples of DNA to be replicated and analysed.

This means that a single DNA molecule can be turned into millions of copies, in a relatively short space of time.

PCR has many uses, including the diagnosis of genetic diseases, detecting low levels of viral infection. It also used in forensic science, allowing the analysis of very small traces of blood and other tissue samples.

There are 4 things required to carry out PCR successfully:
  • Target sample - This contains the template DNA – The DNA that contains the region to be copied. The sample can contain as little as one molecule of DNA to serve as the template.
  • Primer - This is a short strand of DNA that attaches to each end of the target sample, it provides a starting point for the replication process, by priming and laying a foundation for the replication of the DNA.
  • Taq polymerase - An enzyme with relatively high thermostability, that replicates the DNA by adding on free nucleotides in sequence.
  • Nucleotides - These are needed so that the enzyme has the building blocks to work with.
The 3 major steps for PCR are:
  • Heating - The target sample is heated, this step denatures the DNA, unwinding the helix and breaking the bonds. Leaving a single strand of DNA.
  • Temperature reduction - This step allows the primer to start working, by binding to the DNA, and providing a starting place for the replication.
  • Heating - The sample is then heated again, to allow elongation to begin. In this step the enzyme binds to the end of the primer and uses the single strand DNA as the template and incorporates the nucleotides.

PCR has revolutionised DNA replication and analysis.

Once the DNA has been copied it can then be analysed using Electrophoresis.

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