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In the denaturation step, the PCR mixture containing the DNA template, primers, nucleotides, and Taq DNA polymerase is heated to a temperature of approximately 94-96°C. The high temperature causes the double-stranded DNA template to separate into single strands, making it accessible for the primers to bind to the target sequence.

The second step in the PCR cycle is annealing, where the temperature is lowered to a range of 50-65°C depending on the primer sequence. This allows the primers to bind specifically to the complementary sequences on the single-stranded DNA. The primers are short DNA sequences that are designed to match and bind to specific regions of interest on the template DNA. They provide a starting point for DNA polymerase to begin extending the new DNA strands.

The third and final step is the extension or elongation phase. The temperature is increased to approximately 72°C, which is the optimal temperature for the Taq DNA polymerase enzyme to function efficiently. Taq DNA polymerase binds to the primer-template complex and begins adding complementary nucleotides to the 3' end of the primers. This synthesis of the new DNA strands is carried out in the 5' to 3' direction, using the original DNA template as a guide. At the end of the extension step, a new double-stranded DNA molecule has been formed, consisting of one original DNA strand and one newly-synthesized strand. The PCR cycle is repeated multiple times (usually 25-40 cycles) to achieve a significant increase in the amount of the target DNA sequence. Each subsequent cycle amplifies the desired DNA fragment exponentially, creating millions to billions of copies of the target DNA sequence.