What is a nucleoside?

What is a nucleoside?

• A. A nitrogenous base bound to a sugar with a phosphate group.
• B. A nitrogenous base bound to a sugar without a phosphate.
• C. A nucleotide with three phosphate groups.
• D. A chain of nucleotides bound by glycosidic bonds.

Answer: (B)

A nucleoside is a nitrogenous base attached to a sugar (ribose or deoxyribose) with no phosphate group. The bond between the base and the sugar is an N-glycosidic bond, and the absence of phosphate distinguishes it from a nucleotide. When one or more phosphate groups are added, you get a nucleotide; a nucleotide with three phosphates is a triphosphate like ATP. A chain of nucleotides forms DNA or RNA. So the description of a base bound to a sugar without a phosphate matches a nucleoside, while including phosphate describes a nucleotide, and a long chain of nucleotides describes a polynucleotide.

A nucleoside is a nitrogenous base attached to a sugar (ribose or deoxyribose) with no phosphate group. The bond between the base and the sugar is an N-glycosidic bond, and the absence of phosphate distinguishes it from a nucleotide. When one or more phosphate groups are added, you get a nucleotide; a nucleotide with three phosphates is a triphosphate like ATP. A chain of nucleotides forms DNA or RNA. So the description of a base bound to a sugar without a phosphate matches a nucleoside, while including phosphate describes a nucleotide, and a long chain of nucleotides describes a polynucleotide.