Given below is the diagrammatic representation of one of the categories of small molecular weight organic compounds in the living tissues. Identify the category shown and the one blank component “X” in it

Nucleosides are glycosylamines that can be thought of as nucleotides without a phosphate group. A nucleoside consists simply of a nucleobase and a 5-carbon sugar (either ribose or deoxyribose), whereas a nucleotide is composed of a nucleobase, a five-carbon sugar and one or more phosphate groups. In a nucleoside, the base is bound to either ribose or deoxyribose via a β-glycosidic linkage. Examples of nucleosides include cytidine, uridine, adenosine, guanosine, thymidine and inosine. Since in cholesterol and amino acid structures, there is no nucleobase attached to 5 carbon sugar. There is no phosphate group attached in above structure.