What type of bonds link atoms in the DNA backbone?

• A. Hydrogen bonds
• B. Ionic bonds
• C. Covalent bonds
• D. Van der Waals forces

Answer: (C)

The backbone of DNA is a sugar–phosphate chain connected by covalent bonds, specifically phosphodiester bonds. Each linkage forms when the 3' hydroxyl of one deoxyribose reacts with the 5' phosphate of the next nucleotide, creating a strong, continuous polymer that gives the strand its durable structure. The hydrogen bonds you hear about are between complementary bases across the two strands and do not link the sugar–phosphate units themselves. Ionic interactions and van der Waals forces play other roles in molecular interactions and base stacking, but they do not form the backbone linkage. So the bonds that link atoms in the DNA backbone are covalent bonds.