The backbone of DNA is composed of which components?

• A. Deoxyribose and phosphate
• B. Ribose and phosphate
• C. Deoxyribose and sulfate
• D. Glucose and phosphate

Answer: (A)

DNA’s backbone is the sugar-phosphate chain that holds the nucleotides in place. Each nucleotide contains deoxyribose, a five‑carbon sugar, which is linked to the next sugar by a phosphate group through a phosphodiester bond. This repeated deoxyribose–phosphate linkage forms the stable framework of the molecule, with the nitrogenous bases extending inward to pair and create the double helix. The deoxyribose in DNA lacks a 2' hydroxyl group, unlike RNA which uses ribose; that difference explains why the backbone of DNA is built from deoxyribose rather than ribose. The other options aren’t correct because sulfate, glucose, or ribose would not constitute the DNA backbone; ribose is used in RNA, while sulfate and glucose aren’t components of the nucleic acid backbone.