What is a nucleoside?

What is a nucleoside?

• A. A base + sugar
• B. A base + sugar + 1 phosphate
• C. A base + sugar + 3 phosphates
• D. A sugar + 3 phosphates

Answer: (C)

A nucleoside is a building block made of a nitrogenous base attached to a five‑carbon sugar, with no phosphate groups attached. The phosphate groups are what turn a nucleoside into a nucleotide; adding one, two, or three phosphates yields a nucleotide monophosphate, diphosphate, or triphosphate (like ATP), respectively. So the description that fits a nucleoside is base plus sugar only. Descriptions that include phosphate groups describe nucleotides, not nucleosides; for example, base plus sugar plus three phosphates would be a nucleotide triphosphate, not a nucleoside.

A nucleoside is a building block made of a nitrogenous base attached to a five‑carbon sugar, with no phosphate groups attached. The phosphate groups are what turn a nucleoside into a nucleotide; adding one, two, or three phosphates yields a nucleotide monophosphate, diphosphate, or triphosphate (like ATP), respectively. So the description that fits a nucleoside is base plus sugar only. Descriptions that include phosphate groups describe nucleotides, not nucleosides; for example, base plus sugar plus three phosphates would be a nucleotide triphosphate, not a nucleoside.