Which of the following describes the three parts of a nucleotide?

• A. an amino acid
• B. a sugar and a lipid
• C. a sugar, a phosphate group, and one of the four nitrogenous bases
• D. a phosphate group and a glycerol

Answer: (C)

The main concept here is what a nucleotide is made of. A nucleotide has three parts: a five‑carbon sugar, a phosphate group, and a nitrogenous base. The sugar (ribose in RNA or deoxyribose in DNA) forms the backbone, with the phosphate group connecting to the sugar and linking nucleotides together through phosphodiester bonds. The base—adenine, cytosine, guanine, thymine (or uracil in RNA)—provides the genetic code. The other descriptions mix in components from entirely different molecules (amino acids, lipids, or glycerol), which aren’t part of nucleotides. So the description that includes a sugar, a phosphate group, and one of the four nitrogenous bases correctly captures the nucleotide’s structure.