The monomers of RNA nucleic acids consist of three parts. What are those three parts?

• A. A base, ribose, and phosphoric acid.
• B. A base, deoxyribose, and phosphate.
• C. A base, ribose, and sulfate.
• D. A base, ribose, and pyrophosphate.

Answer: (A)

RNA monomers are nucleotides, built from three parts: a nitrogenous base, a five-carbon sugar called ribose, and a phosphate group. The base (adenine, uracil, cytosine, or guanine) provides the informational part of the molecule, while the ribose sugar gives the framework to which the phosphate attaches. The phosphate group links to the sugar and to the phosphate of neighboring nucleotides to form the backbone of the RNA strand through phosphodiester bonds. This trio—base, ribose, and phosphate—is what distinguishes a nucleotide from other molecules. Since this question is about RNA, the sugar is ribose (not deoxyribose, which would indicate DNA). Sulfate or pyrophosphate aren’t the typical monomer components of RNA nucleotides, though pyrophosphate appears in energy-rich contexts, not as the standard nucleotide monomer.