In PCR, what is the purpose of the denaturation step?

• A. To separate the two DNA strands by heating.
• B. To extend new DNA strands by polymerase.
• C. To synthesize primers.
• D. To ligate DNA fragments.

Answer: (A)

Denaturation is about melting the DNA so the two strands separate. By heating to a high temperature, the hydrogen bonds between complementary bases break, turning the double helix into single strands. That separation is crucial because the primers must find and bind to their matching sequences on single-stranded templates, and the DNA polymerase can only copy from those exposed templates. Once the strands are separated, the cycle proceeds to primers binding and then the polymerase extending the new DNA from those primers. This step isn’t about extending DNA, making primers, or ligating fragments—those happen in the other parts of the process.