Which statement describes DNA base pairing and hydrogen bonds?

• A. A pairs with T via two hydrogen bonds; C pairs with G via three hydrogen bonds
• B. A pairs with G via hydrogen bonds; C with T
• C. A pairs with T via two hydrogen bonds; C pairs with G via three hydrogen bonds
• D. All bases pair via covalent bonds

Answer: (C)

DNA base pairing is driven by hydrogen bonds between complementary bases. Adenine forms two hydrogen bonds with thymine, while cytosine forms three hydrogen bonds with guanine. This pairing pattern helps keep the two strands of the double helix the same width and allows the strands to separate easily during replication and transcription because hydrogen bonds can be broken and reformed. Covalent bonds hold the sugar-phosphate backbone together along each strand, not the bases between strands. So the accurate description is that adenine pairs with thymine via two hydrogen bonds and cytosine pairs with guanine via three hydrogen bonds.