Which DNA strand is used as the template for RNA synthesis in transcription?

• A. Coding strand
• B. Template strand
• C. Leading strand
• D. Lagging strand

Answer: (B)

In transcription the template strand is the DNA strand that RNA polymerase reads to build the RNA. The RNA transcript is complementary to this template and is synthesized in the 5' to 3' direction. Because RNA uses uracil instead of thymine, the RNA sequence is identical to the coding (sense) strand except that T is replaced by U. The idea is that the transcription machinery binds the promoter and uses the template strand to determine the sequence of the RNA, while the coding strand simply mirrors the RNA (with T for U). The terms leading and lagging strands come from DNA replication, not transcription, so they aren’t used as the template for RNA synthesis. For example, if the coding strand is 5'-ATG-...-3', the RNA would be 5'-AUG-...-3', and the template strand would be 3'-TAC-...-5'.