Sugar nucleotide metabolism. The formation of activated sugar nucleotides is intrinsically linked to cellular metabolism. For example, the conversion of glucose to pyruvate (Pyr) during glycolysis also forms fructose-6-phosphate (Fruc-6-P), which contributes to the accumulation of the UDP-GNAc pool (UDPGlcNAc and UDP-GalNAc), in a similar manner to glutamine (Gln) and ammonium (NH4+). The content of this pool has a direct effect on the proportion of sialic acid precursors (such as CMP-Neu5Ac) and may impact the antennarity of glycans since UDP-GlcNAc is a substrate for GlcNAc transferase enzymes, which catalyse the addition of glycan chains. Glycan donors and monosaccharides are shown in rectangles. Additional abbreviations are noted elsewhere.