Question

The correct order of steps in Polymerase Chain Reaction (PCR) is

• A. Extension, Denaturation, Annealing
• B. Denaturation, Extension, Annealing
• C. Annealing, Extension, Denaturation
• D. Denaturation, Annealing, Extension

Answer 1

The Correct Option is D

The Polymerase Chain Reaction (PCR) is a technique used to amplify specific segments of DNA. It involves three main steps which cycle repeatedly to gradually build up the desired DNA sequence. The correct order of these steps is crucial for the success of the reaction. Let's examine each step and its purpose:

1. Denaturation:

   The PCR process begins with denaturation, where the double-stranded DNA is heated to around 94-98°C. This high temperature causes the hydrogen bonds between the DNA strands to break, resulting in two single strands of DNA. This is crucial as it sets the stage for the primers to bind to their respective target sequences on these single strands in the next step.

2. Annealing:

   After denaturation, the reaction mixture is cooled to about 50-65°C. This allows the primers to bind, or "anneal," to their complementary sequences on the single-stranded DNA. Primers are short sequences of nucleotides that provide a starting point for DNA synthesis.

3. Extension:

   In the final step, the temperature is raised to the optimal range for the DNA polymerase enzyme, typically 72°C. The polymerase extends the primers, synthesizing new strands of DNA by adding nucleotides that are complementary to the template strands. This results in the duplication of the target DNA segment.

The correct order of these steps is therefore: Denaturation, Annealing, Extension. This order ensures that the DNA is properly replicated in multiple cycles, with each cycle doubling the amount of target DNA sequence.

Thus, the correct option is:
Denaturation, Annealing, Extension