Nucleoside

Definition

A nucleoside is a molecule consisting of a nitrogenous base attached to a five-carbon sugar (ribose or deoxyribose). It lacks the phosphate group that distinguishes it from a nucleotide.

5 Must Know Facts For Your Next Test

1. Nucleosides are building blocks of nucleotides, which form DNA and RNA.
2. The nitrogenous bases in nucleosides can be purines (adenine, guanine) or pyrimidines (cytosine, thymine, uracil).
3. In DNA, the sugar in nucleosides is deoxyribose; in RNA, it is ribose.
4. Nucleosides are linked together by phosphodiester bonds to form the backbone of DNA and RNA strands once they are phosphorylated into nucleotides.
5. Phosphorylation of a nucleoside results in the formation of mono-, di-, or triphosphate nucleotides.

Review Questions

• What components make up a nucleoside?
• How does a nucleoside differ from a nucleotide?
• What types of sugars are found in DNA and RNA nucleosides?

Related terms

Nucleotide:

A molecule composed of a nitrogenous base, a five-carbon sugar, and one or more phosphate groups.

Nitrogenous Base:

An organic molecule with nitrogen atoms that has the chemical properties of a base; examples include adenine, guanine, cytosine, thymine, and uracil.

Phosphodiester Bond:

A covalent bond that forms the backbone of DNA and RNA molecules by linking the sugars of two adjacent nucleotide units.