Describe the mechanism of the polymerase chain reaction.

The polymerase chain reaction (PCR) is basically a series of three-stage cycles, each stage occurring at a different temperature. The three stages are denaturation, annealing and extension.Denaturation takes place at a temperature of about 95℃. When the double-stranded DNA that is to be amplified (ie increased in number) is heated to 95℃, the hydrogen bonds holding the two strands together are broken and the strands are separated. Denaturation is followed by annealing, which occurs at a temperature between 55-70℃. At this stage, primers bind specifically ('anneal') to their complementary sequence in the single-stranded DNA. The third stage is extension, which happens at a temperature of 72℃, which is the optimum temperature for the Taq DNA polymerase enzyme needed at this stage. During extension, the Taq DNA polymerase extends the primers from their 3' ends, thus creating new DNA using the original single strand of DNA as a template (with complementary base pairing and covalent bond formation between deoxynucleotide triphosphates, the bases you add to the template). This 3-stage cycle can then be repeated 30-40 times.