Uracil-containing nucleotides are transcribed from nucleotides containing which base?

• A. Cytosine
• B. Guanine
• C. Adenine
• D. Thymine

Answer: (C)

Transcription creates an RNA strand that is complementary to the DNA template strand, and RNA uses uracil in place of thymine. The base that pairs with uracil in RNA is adenine in the DNA template. So, when the DNA template has adenine, the RNA polymerase inserts uracil opposite it, producing uracil-containing nucleotides in the RNA. If the DNA template had thymine, the RNA would incorporate adenine instead of uracil; cytosine or guanine in DNA would guide the incorporation of cytosine or guanine in RNA, respectively. Thus, uracil-containing nucleotides in RNA come from adenine in the DNA template.