Transcription is carried out by which enzyme?

• A. RNA Polymerase
• B. DNA Polymerase
• C. RNA Ligase
• D. Helicase

Answer: (A)

Transcription uses RNA polymerase to build RNA from a DNA template. This enzyme reads the DNA sequence in the 3' to 5' direction and links ribonucleotides together to form a complementary RNA strand in the 5' to 3' direction, without needing a primer. In bacteria, the RNA polymerase holoenzyme with a sigma factor recognizes promoters to start transcription; in eukaryotes, RNA polymerase II with transcription factors does the job. DNA polymerase, in contrast, makes DNA from a DNA template and requires a primer (and has proofreading). RNA ligase helps join RNA fragments or is involved in RNA processing, not transcription. Helicase unwinds the DNA to allow access, but it does not synthesize RNA.