Nucleosides and nucleotides are both fundamental components of nucleic acids (DNA and RNA), but they have a slight difference in their chemical composition:
Nucleoside:

1. A nucleoside consists of a nitrogenous base (purine or pyrimidine) covalently attached to a sugar molecule (ribose in RNA or deoxyribose in DNA).
2. The attachment between the sugar and the base is through a glycosidic bond.
3. Examples of nucleosides include adenosine, guanosine, cytidine, thymidine, and uridine.
4. Nucleosides do not contain a phosphate group.

Nucleotide:

1. A nucleotide is composed of three parts: a nitrogenous base (purine or pyrimidine), a sugar molecule (ribose or deoxyribose), and one or more phosphate groups.
2. The phosphate group(s) are attached to the 5′ carbon of the sugar molecule.
3. Examples of nucleotides include adenosine monophosphate (AMP), guanosine triphosphate (GTP), cytidine diphosphate (CDP), and thymidine monophosphate (TMP).
4. Nucleotides are the monomers that make up the nucleic acids DNA and RNA.
5. Nucleotides also serve as energy carriers (e.g., ATP) and signaling molecules (e.g., cAMP) in various cellular processes.