In DNA structure, adenine (A) always pairs with which nitrogenous base through hydrogen bonding?

• A. Cytosine (C)
• B. Thymine (T)
• C. Guanine (G)
• D. Uracil (U)

Answer: (B)

Verified step by step guidance

1. Recall the base pairing rules in DNA, which describe how nitrogenous bases pair through hydrogen bonds.
2. Understand that DNA is composed of four bases: adenine (A), thymine (T), cytosine (C), and guanine (G).
3. Remember that adenine (A) pairs specifically with thymine (T) via two hydrogen bonds, ensuring the DNA double helix structure is stable.
4. Note that cytosine (C) pairs with guanine (G) through three hydrogen bonds, which is a different pairing rule.
5. Recognize that uracil (U) is found in RNA, not DNA, and pairs with adenine (A) in RNA instead of thymine.