What is polymerase chain reaction (PCR)?

PCR was developed in the early 80’s by a biochemist named Kary Mullis. He was eventually awarded the Nobel Prize for his work in chemistry. PCR is used to make multiple copies from a very small amount of DNA or a gene. PCR is commonly used in biology labs conducting disease research. It is especially used to detect the absence or presence of genes to assist in identifying infectious pathogens. All from small samples of DNA.

What makes PCR work?

The science behind PCR is simple. Just five ‘ingredients’ are necessary to run a successful PCR test.  These ingredients are:

  1. The sample or DNA template that is to be copied
  2. A short stretch of DNA (also known as a primer) that will trigger the PCR reaction and bind to the DNA the scientist wishes to copy
  3. A DNA nucleotide base (dNTPs). DNA bases are the standard building blocks of DNA and are required to build a new strand of DNA.
  4. Taq ( a polymerase enzyme) that will be added to the fresh DNA bases
  5. A buffer to protect the conditions and help create the reaction.

PCR involves thermal cycling, a process of heating and cooling, which is performed by the machine.

There are three primary stages:

  1. Denaturing – this happens when heating the template DNA causes separation into two single strands.
  2. Annealing – this happens when the temperature is cooled to allow the DNA primer the ability to attach to the present template DNA.
  3. Extending – this happens when the heat is reintroduced to the new strand of DNA.

Each stage is repeated between twenty and forty times. This increases the number of DNA copies present each cycle. The PCR reaction is completed in just a few short hours. In certain cases, high-speed machines can complete the reaction in under an hour. Upon completion, electrophoresis can be deployed to verify the size and quantity of the DNA created.