Which of the following is NOT part of a nucleotide?

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

Answer: (C)

Nucleotides are built from three parts: a sugar, a phosphate group, and a nitrogenous base. The sugar (deoxyribose in DNA or ribose in RNA) forms the main chain, the phosphate group links sugars together to create the backbone, and the nitrogenous base encodes genetic information through base pairing. An amino acid, however, is the building block of proteins, not nucleic acids. Therefore, the component that does not belong to a nucleotide is the amino acid.