Which of the following is a correct sequence of steps in a PCR (Polymerase Chain Reaction) ?

The Polymerase Chain Reaction (PCR) amplifies a specific DNA segment through repeated cycles of three distinct steps.

1. Denaturation
During this step the reaction mixture is heated to around 94–98 °C. The high temperature breaks the hydrogen bonds between the two strands of the DNA double helix, producing two single‑stranded templates that are ready for primer binding.

2. Annealing
The temperature is then lowered to 50–65 °C, allowing short synthetic primers to hybridize (anneal) to their complementary sequences on each single‑stranded template. Proper annealing temperature depends on the primer’s melting temperature (Tm) and ensures specific binding.

3. Extension (or Elongation)
The reaction temperature is raised to the optimal working temperature of the DNA polymerase, typically 72 °C for Taq polymerase. The enzyme adds deoxynucleotide triphosphates (dNTPs) to the 3' end of each primer, synthesizing a new complementary DNA strand along each template.

These three steps—Denaturation, Annealing, Extension—constitute one complete PCR cycle. Repeating the cycle 25–35 times results in exponential amplification of the target DNA fragment.