Carbohydrates are a major component of the diet, and include starch (amylose and amylopectin) and disaccharides such as sucrose, lactose, maltose and, in small amounts, trehalose. Once released from starch or once ingested, sucrose can be degraded into beta-D-fructose and alpha-D-glucose via lysosomal alpha-glucosidase or sucrose-isomaltase. Beta-D-Fructose can be converted to beta-D-fructose-6-phosphate by glucokinase and then to alpha-D-glucose-6-phosphate by the action of glucose phosphate isomerase. Phosphoglucomutase 1 can then act on alpha-D-glucose-6-phosphate (G6P) to generate alpha-D-glucose-1-phosphate. alpha-D-Glucose-1-phosphate (G6P) has several possible fates. It can enter into gluconeogenesis, glycolysis, or the nucleotide sugar metabolism pathway. UDP-glucose pyrophosphorylase 2 can convert alpha-D-glucose-1-phosphate into UDP-glucose, UDP-glucose can then be used to produce D-glucose via trehalose. UDP-glucose can also serve as a precursor to the synthesis of glycogen via glycogen synthase. Glycogen is a starch analogue commonly called an animal starch. Glycogen is found in the cytosol in granules. Glycogen is cleaved and converted to glucose-6-phosphate (G6P) which undergoes glycolysis or can enter the pentose phosphate pathway.

Starch and Sucrose Metabolism References