Nucleotide-sugars are the building blocks for the biosynthesis of polysaccharides and glycoconjugates. Most nucleotide-sugars are synthesized in the cytosol, primarily from dietary sugars, followed by their transport into the endoplasmic reticulum, the Golgi apparatus and the nucleus. In D. melanogaster, the main nucleotide-sugars are UDP-D-glucose (UDP-Glc), UDP-N-acetylglucosamine (UDP-GlcNAc), UDP-D-galactose (UDP-Gal), UDP-N-acetylgalactosamine (UDP-GalNAc), UDP-D-glucuronate (UDP-GlcA), GDP-mannose (GDP-Man), CMP-N-acetylneuraminate (CMP-NeuNAc), GDP-L-fucose (GDP-Fuc) and UDP-D-xylose (UDP-Xyl). Together, they constitute the precursors for the synthesis of glycoproteins, glycolipids and glycosylphosphatidylinositol (GPI) anchors. In addition, UDP-Glc is used to produce glycogen and the disaccharide trehalose, while UDP-GalNAc is used for the synthesis of the polysaccharide chitin. (Adapted from PMID:34939087 and PMID:35536946.)