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How Does The PCR Test Work and When Can It Be Used?

By Natasha Quinton-Hibberd - Biology Student @ St Catharine's College, Oxford


The polymerase chain reaction amplifies DNA in vitro (performed outside of a living organism, for example in a test tube or culture dish). The process occurs in three main steps: DNA strand separation, the annealing of primers and DNA synthesis. During DNA strand separation, the double stranded DNA is heated to 95 degrees Celsius. Consequently, the hydrogen bonds between the base pairs of the parent molecule are broken; the three hydrogen bonds between cytosine and guanine base pairs as well as the two hydrogen bonds between adenine and thymine. This leaves two single strands of DNA that can be used as template strands when the amplification step begins.