In DNA base pairing, which pairing is correct?

In DNA base pairing, which pairing is correct?

• A. A-T and C-G
• B. A-U and C-G
• C. G-C and T-A
• D. A-C and T-G

Answer: (A)

DNA base pairing follows that adenine pairs with thymine and cytosine pairs with guanine. This arrangement keeps the DNA double helix uniform and is stabilized by hydrogen bonds—two between A and T, three between C and G. Uracil appears in RNA instead of thymine, so pairing that involves uracil isn’t correct for DNA. The standard way to express the rule is A-T and C-G, directly stating the two correct pairings. Writing G-C and T-A describes the same relationships but in reverse order, while A-C or T-G are not complementary in DNA.

DNA base pairing follows that adenine pairs with thymine and cytosine pairs with guanine. This arrangement keeps the DNA double helix uniform and is stabilized by hydrogen bonds—two between A and T, three between C and G. Uracil appears in RNA instead of thymine, so pairing that involves uracil isn’t correct for DNA. The standard way to express the rule is A-T and C-G, directly stating the two correct pairings. Writing G-C and T-A describes the same relationships but in reverse order, while A-C or T-G are not complementary in DNA.