What happens to the DNA template during initiation of transcription?

• A. Denaturation (unwinding)
• B. Ligation
• C. Polyadenylation
• D. Replication

Answer: (A)

During initiation of transcription, the DNA template is unwound to expose the bases. RNA polymerase must read the template strand in order to synthesize a complementary RNA strand, so the double helix around the promoter region is locally melted, forming a transcription bubble. This unwinding breaks the hydrogen bonds between base pairs, separating the two strands so the template strand becomes accessible as a single strand for base pairing. This opening is localized and temporary—the enzyme stays at the promoter as it begins RNA synthesis, and the bubble moves along with the advancing enzyme as transcription proceeds. The other processes mentioned (joining DNA ends, adding a poly-A tail to RNA, or copying the entire DNA for replication) do not describe what happens to the DNA template during transcription initiation.