The first step in DNA replication is the breaking of the _____ that exists between the nitrogen bases.

• A. Covalent bonds
• B. Hydrogen bonds
• C. Peptide bonds
• D. Ionic bonds

Answer: (B)

During DNA replication, the two strands must unzip so each can serve as a template. The bonds holding the base pairs together are hydrogen bonds between complementary bases. These are relatively weak and break easily, allowing the strands to separate at the replication fork and enabling the synthesis of new strands. In contrast, the covalent bonds in the sugar-phosphate backbone are much stronger and stay intact during this initial separation; breaking them would fragment the DNA rather than unzip it. Peptide bonds connect amino acids in proteins, and ionic interactions are not the main stabilizing force in the DNA double helix, so they are not the bonds disrupted at the start of replication.