Question

Arrange steps of PCR:
A. Extension
B. Denaturation
C. Annealing

• A. B $\rightarrow$ C $\rightarrow$ A
• B. C $\rightarrow$ B $\rightarrow$ A
• C. B $\rightarrow$ A $\rightarrow$ C
• D. A $\rightarrow$ C $\rightarrow$ B

Hint:

Think of the process logically: you must first separate the strands (Denature), then attach the starting blocks (Anneal primers), and finally build the rest of the wall (Extend).

Answer 1

The Correct Option is A

Polymerase Chain Reaction (PCR) is a widely used technique in molecular biology to amplify specific DNA segments. The process involves three principal steps that cycle repeatedly to produce millions of copies of the DNA. Let's explain these steps in the correct order:

1. Denaturation: The first step is heating the reaction mixture to a high temperature, usually around 94-98°C, for 20 to 30 seconds. This high temperature causes the double-stranded DNA to denature, meaning the two strands are separated.
2. Annealing: Following denaturation, the temperature is rapidly decreased, typically to 50-65°C, for 20 to 40 seconds. This allows the primers to anneal or bind to their complementary sequences on the single-stranded DNA templates. The primers are short DNA sequences that are necessary for the initiation of DNA synthesis.
3. Extension: Finally, the temperature is increased to the optimal temperature for the DNA polymerase used, usually around 72°C. In this step, the polymerase enzyme extends the primers to form a new DNA strand by adding nucleotides complementary to the template strand.

The correct sequence for PCR is therefore: Denaturation, Annealing, and Extension, which corresponds to option B → C → A in the given choices.

This ordered sequence is crucial for the accuracy and efficiency of DNA amplification during PCR.