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The figure below shows three steps (A, B, C) of Polymerase Chain Reaction (PCR). Select the option giving correct identification together with what it represents.

1. A - Denaturation at a temperature of about 98°C separating the two DNA strands.
2. B - Annealing with two sets of primers.
3. C - Extension in the presence of heat stable DNA polymerase.
4. D - None of the above.

Correct answer: C - Extension in the presence of heat stable DNA polymerase.

Solution

In PCR, the extension step is when DNA polymerase adds nucleotides to the primers to synthesize new strands, and it must be heat-stable because the reaction has already been heated. That is why option C correctly identifies the step and its function.

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