Which statement best describes complementary base pairing?

Which statement best describes complementary base pairing?

• A. In DNA, thymine pairs with adenine; guanine pairs with cytosine.
• B. In DNA, adenine pairs with cytosine; guanine pairs with thymine.
• C. In RNA, adenine pairs with cytosine; guanine pairs with uracil.
• D. In RNA, thymine pairs with adenine; cytosine pairs with guanine.

Answer: (A)

Complementary base pairing in DNA means bases pair with their specific partners: adenine with thymine and guanine with cytosine. This pairing, driven by hydrogen bonds and the need to keep the double helix width constant, lets each strand serve as a perfect template for the other during replication. Adenine-thymine forms two hydrogen bonds, while guanine-cytosine forms three, providing stability to the DNA molecule. In RNA, thymine is replaced by uracil, so the pairing is adenine with uracil and guanine with cytosine. That’s why the statement describing DNA A–T and G–C pairing best captures complementary base pairing.

Complementary base pairing in DNA means bases pair with their specific partners: adenine with thymine and guanine with cytosine. This pairing, driven by hydrogen bonds and the need to keep the double helix width constant, lets each strand serve as a perfect template for the other during replication. Adenine-thymine forms two hydrogen bonds, while guanine-cytosine forms three, providing stability to the DNA molecule. In RNA, thymine is replaced by uracil, so the pairing is adenine with uracil and guanine with cytosine. That’s why the statement describing DNA A–T and G–C pairing best captures complementary base pairing.