Essay What is the Polymerase Chain Reaction (PCR)

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The polymerase chain reaction or PCR for short can be used to create many copies of DNA. This allows the DNA to then be visualized using a dye like ethidium bromide after gel electrophoresis. The process has been refined over the years, however the basic steps are similar.

The first is to denature dsDNA through heating to ~96 °C. This separates the two strands of DNA. The exact temperature to be used can be calculated with Tm = 4oC x (no. of G & C) + 2oC x (no. of A & T). Tm is the melting point of the strands and to supply the number of G, C, A, & T ‘s the primer is used.
Annealing of primers is then possible when the temperature cools down to 37-65 °C.

Extension from these primers can be done through the use of heat stable (has to
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However it is a known carcinogen and therefore alternatives have been developed. These, for instance gelred, can be used without the use of UV lighting. However they are often a lot more expensive.

A general issue is that PCR techniques can be very sensitive; any contamination can be amplified. This in combination with the improvements in technique seen over the last few years can mean that for instance in forensics, extensive care needs to be taken when handling samples to prevent contamination. The interpretation of results can also prove tricky for levels of contamination (or DNA that was there due to circumstances unrelated to the crime) that may not have been noticeable with earlier techniques can point the blame to someone who was in fact innocent.

However forensics is not the only area that has been advanced by PCR techniques. Diseases diagnosis can be made much more accurately and quickly. The diagnosis however is not just limited to infectious diseases caused by bacteria, tumours can also be analysed. Therefore it may become apparent if it is the result of a general genetic abnormality or simply an untimely mutation. Viruses similarly can be detected if someone is infected, along with the viral load; this allows disease progression to be monitored.
Genetic mutations are important for tracking disease abnormalities and if there are any causal links between unsuspecting genes and diseases. Not
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