In PCR, which process involves primers binding to complementary DNA sequences?

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

Answer: (A)

The process where primers bind to their complementary sequences on the target DNA during PCR is annealing. After the DNA is denatured, the reaction cools to a temperature that allows short primers to pair with their matching regions on each single-stranded DNA. This establishes starting points for DNA polymerase to extend from, which happens in the next step. Transcription is RNA synthesis and isn’t part of PCR, and denaturation is the heating step that separates the DNA strands, while extension is when polymerase copies DNA from the primers. So the binding of primers to their targets is annealing.