In the context of DNA structure, how many hydrogen bonds are formed between each complementary base pair of adenine-thymine (A-T) and guanine-cytosine (G-C)?

• A. A-T pairs have 2 hydrogen bonds; G-C pairs have 3 hydrogen bonds.
• B. A-T pairs have 3 hydrogen bonds; G-C pairs have 2 hydrogen bonds.
• C. Both A-T and G-C pairs have 3 hydrogen bonds.
• D. Both A-T and G-C pairs have 2 hydrogen bonds.

Answer: (A)

Verified step by step guidance

1. Recall the basic structure of DNA, where nucleotides pair specifically: adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C).
2. Understand that hydrogen bonds are the forces that hold these complementary bases together, contributing to the stability of the DNA double helix.
3. Remember the specific number of hydrogen bonds formed between each base pair: adenine and thymine form fewer hydrogen bonds compared to guanine and cytosine.
4. Specifically, adenine (A) pairs with thymine (T) through 2 hydrogen bonds, which makes this pair slightly less stable than the G-C pair.
5. Guanine (G) pairs with cytosine (C) through 3 hydrogen bonds, providing greater stability to the DNA structure in regions rich in G-C pairs.