Practice question

A PCR cycle comprises three precisely controlled steps governed by temperature. Denaturation at 94-95°C separates double-stranded DNA into single strands by breaking hydrogen bonds. Annealing at 50-65°C allows short synthetic oligonucleotide primers to bind to complementary sequences on each template strand via Watson-Crick base pairing and electrostatic stabilization. Extension at 72°C enables Taq polymerase to elongate primers synthesizing new strands. If primer binding fails during annealing, initiation cannot occur and no amplicon is generated. Thus productive primer-template hybridization during this stage determines specificity and efficiency.