How do nucleosides differ from nucleotides?

How do nucleosides differ from nucleotides?

• A. Nucleoside is base + sugar; nucleotide adds a phosphate group.
• B. Nucleoside is sugar + phosphate; nucleotide is base + sugar
• C. Nucleoside contains phosphate; nucleotide contains no phosphate
• D. Nucleoside is base + phosphate; nucleotide is base + sugar

Answer: (A)

The key difference is whether a phosphate group is present. A nucleoside is just the nitrogenous base attached to a sugar (ribose or deoxyribose) with no phosphate. A nucleotide includes that same base-and-sugar unit plus one or more phosphate groups. Those phosphates are what enable nucleotides to form the phosphodiester backbone of DNA and RNA and to store or transfer energy in molecules like ATP. So the correct idea is that a nucleoside is base + sugar, while a nucleotide adds the phosphate group.

The key difference is whether a phosphate group is present. A nucleoside is just the nitrogenous base attached to a sugar (ribose or deoxyribose) with no phosphate. A nucleotide includes that same base-and-sugar unit plus one or more phosphate groups. Those phosphates are what enable nucleotides to form the phosphodiester backbone of DNA and RNA and to store or transfer energy in molecules like ATP. So the correct idea is that a nucleoside is base + sugar, while a nucleotide adds the phosphate group.