RNA molecules differ from DNA molecules because only RNA typically:

• A. is composed of deoxyribose sugar in its backbone
• B. forms a stable double helix with complementary base pairing throughout its length
• C. contains the nitrogenous base uracil instead of thymine
• D. contains the nitrogenous base thymine instead of uracil

Answer: (C)

Verified step by step guidance

1. Recall the structural differences between RNA and DNA molecules, focusing on sugar type, nitrogenous bases, and typical molecular structure.
2. Identify the sugar present in RNA, which is ribose, and contrast it with DNA, which contains deoxyribose sugar.
3. Consider the nitrogenous bases found in RNA and DNA: RNA contains adenine, guanine, cytosine, and uracil, while DNA contains adenine, guanine, cytosine, and thymine.
4. Understand that RNA usually exists as a single-stranded molecule and does not form a stable double helix like DNA does.
5. Conclude that the unique feature of RNA compared to DNA is that RNA contains uracil instead of thymine.