Which description of transcription initiation is accurate?

• A. RNA polymerase binds to the promoter region and unwinds DNA to start RNA synthesis.
• B. DNA polymerase unwinds DNA to begin RNA synthesis.
• C. Ribosomes attach to DNA to transcribe it.
• D. mRNA is translated into protein in the nucleus.

Answer: (A)

Transcription initiation starts when RNA polymerase binds to the promoter region on DNA. This binding positions the enzyme and causes local unwinding of the DNA, creating a transcription bubble so RNA polymerase can start adding RNA nucleotides complementary to the template strand. This process specifically describes transcription, not replication or translation. The other descriptions mix in roles from different processes: DNA polymerase builds DNA, not RNA; ribosomes translate RNA into protein, not transcribe DNA; translation of mRNA into protein occurs in the cytoplasm (not the nucleus in eukaryotes).