In double-stranded DNA, what is the correct base-pairing rule (Watson–Crick base pairing)?

• A. A pairs with U, and G pairs with C.
• B. A pairs with T, and G pairs with C.
• C. A pairs with G, and C pairs with T.
• D. A pairs with C, and G pairs with T.

Answer: (B)

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 Watson–Crick base pairing describes how these bases pair specifically in double-stranded DNA to maintain a consistent structure.
3. Remember the key rule: adenine (A) pairs with thymine (T) through two hydrogen bonds, and guanine (G) pairs with cytosine (C) through three hydrogen bonds.
4. Note that uracil (U) is found in RNA, not DNA, so A does not pair with U in DNA.
5. Therefore, the correct base-pairing rule in double-stranded DNA is: \(A \leftrightarrow T\) and \(G \leftrightarrow C\).