In the structure of DNA, which nitrogenous base pairs with thymine?

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

Answer: (B)

Verified step by step guidance

1. Recall that DNA is composed of four nitrogenous bases: adenine (A), thymine (T), cytosine (C), and guanine (G).
2. Understand that base pairing in DNA follows Chargaff's rules, where adenine pairs specifically with thymine, and cytosine pairs with guanine.
3. Recognize that uracil is not found in DNA; it is a base present in RNA and pairs with adenine there instead of thymine.
4. Identify that thymine forms two hydrogen bonds with adenine, stabilizing the DNA double helix structure.
5. Conclude that the nitrogenous base that pairs with thymine in DNA is adenine.