Polymerase Chain Reaction (PCR)

There are three stages to PCR: denaturation, heating, and extension.

In the first stage, denaturation, the reaction tube in the thermal cycler is heated to 95 degrees Celsius. The high heat denatures DNA by breaking the hydrogen bonds; the double helix is broken into single strands. In the second stage, annealing, the temperature is cooled to 60 degrees Celsius to allow DNA primers to form H-bonds with their complementary bases at 3' end at both strands. In the third stage, extension, the temperature is increased to 72 degrees celsius. Taq DNA polymerase binds to DNA template where primer has annealed. Complementary nucleotides are added to 3' end of both primers, thus catalysing synthesis of a new daughter strand. Chain reaction occurs as the products of previous reactions are used as the reactants in the next cycle.