Which stage in PCR is used to separate DNA strands by heating?

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

Answer: (C)

Denaturation is the stage where the DNA double helix is melted into single strands by heating to a high temperature that disrupts the hydrogen bonds between base pairs. This separation creates single-stranded templates needed for primers to bind in the next step. Typically, this heating occurs around 94–98°C, breaking the bonds so that the polymerase can access the template in the subsequent step. The other stages involve different roles: annealing is when primers bind to their complementary sequences at a cooler temperature, and extension is when the polymerase extends from those primers to synthesize new DNA strands. The key idea is that only denaturation uses heat specifically to separate the strands, enabling the cycle to continue.