The double helix of DNA is stabilized mainly by which type of bonds?

• A. Hydrogen bonds
• B. Covalent bonds
• C. Ionic bonds
• D. Hydrophobic interactions

Answer: (A)

Hydrogen bonding between complementary bases is what primarily holds the two DNA strands together. Adenine pairs with thymine using two hydrogen bonds, and guanine pairs with cytosine using three hydrogen bonds. This network of many relatively weak bonds provides enough stability for the double helix while still allowing strands to separate when needed for replication or transcription. The covalent phosphodiester bonds along each strand keep the backbone intact, but they don’t link the two strands to each other. Ionic interactions aren’t a major factor in the helix’s stability, and while base stacking driven by hydrophobic effects adds overall stability, the main force that stabilizes the double helix is hydrogen bonding between bases.