Which statement describes complementary base pairing in DNA?

Which statement describes complementary base pairing in DNA?

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

Answer: (A)

Complementary base pairing in DNA means that specific bases pair together to form the double helix: adenine pairs with thymine, and cytosine pairs with guanine. This pairing is stabilized by hydrogen bonds—two between A and T, and three between C and G—and by the fit of the bases that keeps the DNA backbone uniformly spaced. That is why the statement describing A with T and C with G is the correct description for DNA. The other pairings would not provide the proper hydrogen-bonding pattern or would involve uracil (A with U), which is found in RNA, not DNA.

Complementary base pairing in DNA means that specific bases pair together to form the double helix: adenine pairs with thymine, and cytosine pairs with guanine. This pairing is stabilized by hydrogen bonds—two between A and T, and three between C and G—and by the fit of the bases that keeps the DNA backbone uniformly spaced. That is why the statement describing A with T and C with G is the correct description for DNA. The other pairings would not provide the proper hydrogen-bonding pattern or would involve uracil (A with U), which is found in RNA, not DNA.