State and explain the principles of the Polymerase Chain Reaction (PCR)

Firstly, PCR is used to amplify DNA so that it can be used in analysis. It is particularly useful in processes like forensic science to identify DNA samples left behind at a crime scene. The process begins with a sample of the DNA being mixed with DNA nucleotides, DNA primers, Magnesium ions and the thermostable enzyme Taq DNA Polymerase. This mixture is then heated to around 95 degrees celcius to denature the DNA strand and break the hydrogen bonds between the two DNA strands. Then the mixture is cooled as this allows the DNA Primers to anneal to each DNA strand. This is important as now the Taq DNA polymerase can bind to the DNA primer and elongate the chain in the 5' to 3' direction and produce new identical double-stranded DNA. The Magnesium ions act as cofactors to the enzyme Taq DNA Polymerase.Whilst the process repeats in cycles, the amount of DNA increases exponentially.