UDP-GlcNAc is a nucleotide sugar consisting of the nucleotide uridine 5-diphosphate and a phosphate-bound monosaccharide, N-acetylglucosamine. Nucleotide sugars are the activated forms of monosaccharides required for cellular metabolism and biosynthesis reactions. UDP-GlcNAc serves as a donor substrate for N-acetylglucosaminyltransferases in the biosynthesis of N-acetylglucosamine-containing glycans.