In the double helix structure of DNA, which nitrogenous base forms hydrogen bonds with adenine?

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

Answer: (D)

Verified step by step guidance

1. Recall that DNA is composed of four nitrogenous bases: adenine (A), thymine (T), guanine (G), and cytosine (C).
2. Understand that base pairing in DNA follows Chargaff's rules, where adenine pairs specifically with thymine, and guanine pairs with cytosine.
3. Recognize that the pairing occurs through hydrogen bonds: adenine forms two hydrogen bonds with thymine.
4. Note that uracil is not found in DNA; it replaces thymine in RNA and pairs with adenine there.
5. Therefore, the nitrogenous base that forms hydrogen bonds with adenine in DNA is thymine.