What is the role of hydrogen bonds in DNA base pairing?

• A. They form between sugar and phosphate in the backbone
• B. They connect nucleotides within a single strand
• C. They hold bases together across the two strands
• D. They link amino acids

Answer: (C)

The key idea is that hydrogen bonds stabilize the DNA double helix by connecting complementary bases across the two strands. Adenine pairs with thymine using two hydrogen bonds, and cytosine pairs with guanine using three hydrogen bonds. These non-covalent interactions hold the bases together between the strands, forming the base pairs that create the helical structure. The backbone’s sugar-phosphate linkage is a covalent bond, not hydrogen bonds, and it does not connect bases. Hydrogen bonds also do not link amino acids—that's the role of peptide bonds in proteins. So the role of hydrogen bonds in base pairing is to hold bases together across the two strands, enabling precise, complementary pairing and allowing the strands to separate when needed for replication or transcription.