Which type of bond connects the backbone of DNA?

• A. Phosphodiester bonds
• B. Glycosidic bonds
• C. Peptide bonds
• D. Hydrogen bonds

Answer: (A)

DNA's backbone is a repeating sugar–phosphate chain. The phosphate of one nucleotide bonds to the 3' carbon of the sugar of the next nucleotide via a phosphodiester bond, a covalent linkage that forms the continuous backbone of the molecule. This covalent connection gives the backbone its strength and rigidity, while the bases extend inward and pair with their complements through hydrogen bonds to hold the two strands together. Other bond types—glycosidic bonds linking a base to its sugar within a nucleotide, and peptide bonds joining amino acids in proteins—do not connect the DNA backbone. So the bonds that connect the backbone are phosphodiester bonds.