In contrast to RNA, DNA contains which nitrogenous base instead of uracil?

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

Answer: (B)

Verified step by step guidance

1. Recall the four nitrogenous bases found in RNA: adenine (A), guanine (G), cytosine (C), and uracil (U).
2. Recall the four nitrogenous bases found in DNA: adenine (A), guanine (G), cytosine (C), and thymine (T).
3. Understand that the key difference between RNA and DNA bases is that DNA contains thymine (T) instead of uracil (U), which is found in RNA.
4. Recognize that thymine pairs with adenine in DNA through two hydrogen bonds, similar to how uracil pairs with adenine in RNA.
5. Therefore, the nitrogenous base present in DNA but not in RNA, replacing uracil, is thymine.