Nucleotides containing Uracil are transcribed from nucleotides that must contain a...

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

Answer: (D)

In transcription, the RNA strand is built to be complementary to the DNA template strand. Uracil in RNA pairs with adenine in DNA, so whenever an RNA nucleotide is uracil, the DNA template must have adenine opposite it (the coding DNA strand would have thymine, but the template strand provides adenine to pair with U). Therefore, nucleotides containing uracil in the transcript come from positions in DNA that contain adenine. The other bases don’t explain uracil incorporation: cytosine pairs with guanine, guanine with cytosine, and thymine in DNA pairs with adenine in RNA, not uracil.