Which term best describes a single unit of DNA or RNA that includes sugar, phosphate, and base?

Which term best describes a single unit of DNA or RNA that includes sugar, phosphate, and base?

• A. Nucleoside
• B. Monomer
• C. Base
• D. Nucleotide

Answer: (D)

A nucleotide is the basic unit that makes up DNA and RNA, carrying three essential components: a sugar (deoxyribose in DNA or ribose in RNA), a phosphate group, and a nitrogenous base. This combination is what builds the nucleic acid chain through phosphodiester bonds, linking the sugar of one unit to the phosphate of the next and forming the sugar–phosphate backbone with the base protruding to store genetic information. The information content comes from the sequence of bases, while the sugar–phosphate backbone provides structure. A nucleoside, by comparison, has only sugar plus base and lacks the phosphate group, so it isn’t the actual monomer used to assemble nucleic acids. A base alone is just one component of a nucleotide, not the complete unit that forms the polymer. A monomer is a general term for the single repeating unit in polymers and isn’t specific to nucleic acids in the way nucleotide is.

A nucleotide is the basic unit that makes up DNA and RNA, carrying three essential components: a sugar (deoxyribose in DNA or ribose in RNA), a phosphate group, and a nitrogenous base. This combination is what builds the nucleic acid chain through phosphodiester bonds, linking the sugar of one unit to the phosphate of the next and forming the sugar–phosphate backbone with the base protruding to store genetic information. The information content comes from the sequence of bases, while the sugar–phosphate backbone provides structure.

A nucleoside, by comparison, has only sugar plus base and lacks the phosphate group, so it isn’t the actual monomer used to assemble nucleic acids. A base alone is just one component of a nucleotide, not the complete unit that forms the polymer. A monomer is a general term for the single repeating unit in polymers and isn’t specific to nucleic acids in the way nucleotide is.