In DNA, which base-pairing is incorrect under standard Watson-Crick pairing rules?

• A. A pairs with T
• B. C pairs with G
• C. A pairs with C
• D. G pairs with C

Answer: (C)

Verified step by step guidance

1. Recall the standard Watson-Crick base pairing rules in DNA, which state that adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G).
2. Understand that these pairings are based on hydrogen bonding patterns: A forms two hydrogen bonds with T, and C forms three hydrogen bonds with G, ensuring stable and specific pairing.
3. Identify the given options and compare each to the standard rules: A pairs with T (correct), C pairs with G (correct), G pairs with C (correct), and A pairs with C (not standard).
4. Recognize that A pairing with C is incorrect because these bases do not form the proper hydrogen bonds required for stable Watson-Crick pairing.
5. Conclude that the incorrect base pairing under standard Watson-Crick rules is A pairs with C.