What is the difference between a nucleoside and a nucleotide?

The primary difference between a nucleoside and a nucleotide lies in their chemical structures and components:

Nucleoside:

A nucleoside consists of two components: a nitrogenous base and a five-carbon sugar (either ribose or deoxyribose).
It does not have any phosphate groups attached to it.
Examples include adenosine (adenine + ribose) and thymidine (thymine + deoxyribose).
Nucleotide:

A nucleotide is composed of three components: a nitrogenous base, a five-carbon sugar (either ribose or deoxyribose), and one or more phosphate groups.
The presence of the phosphate group(s) is what distinguishes a nucleotide from a nucleoside.
Nucleotides can exist as monophosphates (one phosphate group), diphosphates (two phosphate groups), or triphosphates (three phosphate groups).
Examples include adenosine triphosphate (ATP), which has adenine, ribose, and three phosphate groups, and cytidine monophosphate (CMP), which has cytosine, ribose, and one phosphate group.
In summary, while both nucleosides and nucleotides contain a nitrogenous base and a sugar, nucleotides have additional phosphate groups, which nucleosides lack. This difference is crucial for their roles in biological processes, such as energy transfer, signaling, and forming the backbone of nucleic acids (DNA and RNA).