Which pair of nitrogen bases are correctly matched in the structure of DNA?

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

Answer: (B)

Verified step by step guidance

1. Recall the base pairing rules in DNA, which are based on complementary nitrogenous bases forming hydrogen bonds.
2. Identify the purines and pyrimidines: Adenine (A) and Guanine (G) are purines, while Thymine (T) and Cytosine (C) are pyrimidines.
3. Remember that in DNA, a purine always pairs with a pyrimidine to maintain a uniform width of the DNA double helix.
4. Use Chargaff's rules, which state that Adenine pairs with Thymine, and Guanine pairs with Cytosine.
5. Conclude that the correctly matched pair in DNA is Adenine and Thymine, as they form two hydrogen bonds and fit the complementary base pairing rule.