List and briefly describe the three main steps of the Polymerase Chain Reaction (PCR).

Step-by-step solution

1. State the first step: Denaturation, where the reaction mixture is heated to about $94-95^{c}irc\text{C}$ to separate the double‑stranded DNA into single strands.
2. State the second step: Annealing, where the temperature is lowered to $50-65^{c}irc\text{C}$ so that the short forward and reverse primers can hybridise (bind) to their complementary sequences on the template strands.
3. State the third step: Extension (or elongation), where the temperature is raised to the optimum for Taq DNA polymerase ($72^{c}irc\text{C}$) and the enzyme adds nucleotides to the 3' ends of the primers, synthesising new DNA strands.
4. Mention that these three steps constitute one PCR cycle and are repeated 25–35 times to amplify the target DNA exponentially.

Concept tested: PCR process

Published 18 September 2026 · How this solution was prepared and checked