Compared to covalent bonds in the DNA backbone, how do hydrogen bonds between base pairs compare in strength?

• A. They are stronger than covalent bonds.
• B. They have the same strength as covalent bonds.
• C. They are weaker than covalent bonds.
• D. They do not exist between base pairs.

Answer: (C)

The main concept is that bond strength depends on bond type: covalent bonds form the DNA backbone and are very strong, while hydrogen bonds between base pairs are non-covalent attractions and are much weaker. Each base pair is held together by several hydrogen bonds—two for A–T and three for G–C—but even collectively these are far weaker than the covalent phosphodiester bonds that make up the sugar–phosphate backbone. This weaker, reversible nature of hydrogen bonds explains why the two strands can be separated during replication and transcription, while the backbone remains intact. So, hydrogen bonds between base pairs are weaker than the covalent bonds in the DNA backbone.