What is the term used for the phosphate ester of a nucleoside?

The term used for the phosphate ester of a nucleoside is a nucleotide. A nucleotide consists of three components: a nitrogenous base, a five-carbon sugar (ribose in RNA and deoxyribose in DNA), and one or more phosphate groups. When a phosphate group is added to a nucleoside (which is composed of only the sugar and nitrogenous base), it forms a nucleotide, which serves as the building block for nucleic acids like DNA and RNA.

Nucleotides play critical roles in cellular processes, including serving as energy carriers (e.g., ATP) and as signaling molecules. Thus, the relationship between nucleosides and nucleotides is fundamental to molecular biology.