Which is required for transcription to occur on a gene?

• A. RNA nucleotides
• B. DNA ligase
• C. Ribosomes and tRNA
• D. Spliceosome

Answer: (A)

Transcription requires building a new RNA strand using RNA nucleotides as the raw material. RNA polymerase couples these nucleotides to the growing chain, reading the DNA template and adding adenine, uracil, cytosine, and guanine in the correct order to form the complementary RNA sequence. Without RNA nucleotides, the RNA cannot be synthesized at all. The other components have roles in different steps or processes: DNA ligase is involved in sealing breaks in DNA, not in transcription; ribosomes and tRNA are the machinery for translation, not transcription; and the spliceosome processes pre-mRNA after it’s made, removing introns, which is not required for transcription to occur. Therefore, RNA nucleotides are essential for transcription to take place.