Phosphate, sugar, and a nitrogen base make up which biomolecule's basic units?

• A. Nucleotides
• B. Amino acids
• C. Carbohydrates
• D. Lipids

Answer: (A)

Phosphate, sugar, and a nitrogen base assemble the monomer that forms nucleic acids. This unit, called a nucleotide, combines a phosphate group with a five‑carbon sugar (deoxyribose in DNA or ribose in RNA) and a nitrogenous base. When nucleotides link, they form a sugar–phosphate backbone with the bases extending outward to carry genetic information, enabling base pairing and the storage and transmission of hereditary instructions.

Amino acids are the building blocks of proteins, each with an amino and a carboxyl group. Carbohydrates are made from sugar units (monosaccharides), not a phosphate–sugar–base combo. Lipids are built from fatty acids and glycerol (or other nonpolar backbones) and may include phosphate in some structures, but they do not use a nitrogenous base as a defining component.