Figure 1: Accessory pathways of glucose metabolism:

Glucose is converted to glucose-6-phosphate once it enters the cell via glucose transporters (GLUT1 and GLUT4). Glucose can be oxidized via glycolysis to pyruvate which enters TCA cycle in mitochondria to complete glucose oxidation. Alternatively, glucose can enter into polyol pathway and converted to sorbitol via rate-limiting aldose reductase (ALDR) enzyme. Glucose-6-P can be channeled into Pentose Phosphate pathway by rate-limiting glucose-6-phosphate dehydrogenase (G6PD), generating pentose sugars for nucleotide synthesis and NADPH. Pentose sugar, ribose generated from the pentose phosphate pathway is converted to ribitol and subsequently to CDP-ribitol by ribitol-5-phosphate cytidylyltransferase (ISPD), and is conjugated with α-dystroglycan (DAG1) as a glycosylation motif by fukutin-related protein (FKRP) enzyme. Fructose-6-phophate, a glycolytic intermediate can be channeled into the hexosamine biosynthetic pathway by rate-limiting glutamine fructose-6-phosphate amidotransferase (GFAT) and converted to UDP-GlcNAc used for glycosylation of proteins. Additionally, glycolytic intermediate 3-phosphoglycerate enters one-carbon metabolism pathway by the rate-limiting, phosphoglycerate dehydrogenase (PHGDH) and among other steps, interconversion of glycine and serine by serine hydroxymethyl transferase (SHMT), thereby generating one-carbon units for nucleotide and NADPH synthesis.