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

The correct option is Denaturation, Annealing, Extension.

Polymerase Chain Reaction (PCR) is a molecular biology technique used to amplify a specific segment of DNA through repeated cycles of heating and cooling. Each cycle consists of three sequential steps:

1. Denaturation:
The reaction mixture is heated to a high temperature, typically between 94 °C and 98 °C. This high temperature breaks the hydrogen bonds between the complementary bases of the double-stranded DNA template, separating it into two single strands that serve as templates for the next step.

2. Annealing:
The temperature is lowered, usually to a range of 50 °C to 65 °C. This allows short DNA sequences called primers to bind (anneal) to their complementary target sequences on the single-stranded template DNA.

3. Extension (Elongation):
The temperature is raised to the optimal operating temperature for the DNA polymerase enzyme, which is typically around 72 °C. A heat-stable DNA polymerase (such as Taq polymerase) extends the primers by adding free deoxynucleoside triphosphates (dNTPs) in the 5' to 3' direction, synthesizing a new complementary DNA strand.

By repeating these three steps in sequence, the amount of the target DNA sequence is doubled in each cycle, leading to exponential amplification.