Which feature most reliably differentiates RNA from DNA in most cells?

• A. RNA is found only in the nucleus, whereas DNA is found only in the cytoplasm.
• B. RNA is always double-stranded and uses thymine, whereas DNA is always single-stranded and uses uracil.
• C. RNA has a phosphate backbone but DNA does not.
• D. RNA typically contains ribose (with a 2′ $-OH$) and uracil, whereas DNA contains deoxyribose (2′ $-H$) and thymine.

Answer: (D)

Verified step by step guidance

1. Understand the structural differences between RNA and DNA, focusing on their sugar components and nitrogenous bases.
2. Recall that RNA contains the sugar ribose, which has a hydroxyl group (-OH) attached to the 2' carbon, while DNA contains deoxyribose, which lacks this hydroxyl group and has only a hydrogen (-H) at the 2' carbon.
3. Note the difference in nitrogenous bases: RNA uses uracil instead of thymine, which is found in DNA.
4. Recognize that RNA is typically single-stranded and DNA is usually double-stranded, but this is not the most reliable distinguishing feature since exceptions exist.
5. Conclude that the most reliable feature to differentiate RNA from DNA is the presence of ribose with a 2' hydroxyl group and uracil in RNA, versus deoxyribose with a 2' hydrogen and thymine in DNA.