CBSE Class 12-science Answered

The PCR cycle consists of three main stages: denaturation, annealing and extension.

1. Denaturation: During this step, the temperature increases to around 95-98°C for 15-30 seconds. The high temperature causes the double-stranded DNA template to denature, resulting in two single-stranded DNA templates.
2. Annealing: This step involves lowering the temperature to around 50-56°C for specific amplification and 36°C for aspecific amplification. At this temperature, the primers bind to the single-stranded DNA templates to provide a starting point for the polymerase enzyme.
3. Extension: The temperature is raised to around 72-75°C for 15-30 seconds during this step. The polymerase enzyme extends the primers by adding nucleotides to the 3' end of the DNA template, creating a new double-stranded DNA molecule.