10-2 Glycogen (starch) metabolism Figures: Stryer-5ed; chapter: 21 Lehninger-4ed; chapters: 7, 15, 23 The structure of starch amylopectin Branch points occur every 24 to 30 residues! The structure of amylose The structure of glycogen More branched and compact: branch points occur every 8 to 12 residues! Glycogen (starch) degradation (glycogenolysis) Pyridoxal phosphate cofactor (also in amino acid metabolism) Glycogen synthesis (glycogenesis) D -Glucose + ATP D -glucose-6-phosphate + ADP (hexokinase) Glucose-6-phosphate glucose-1-phosphate (phosphoglucomutase) Glucose-1-phosphate + UTP UDP-glucose + PP i (UDP-Glc pyrophosphorylase) UDP-glucose is the substrate for glycogen synthesis ADP-glucose is the substrate for starch synthesis in plants The cost of converting Glc-6-P into glycogen: Glucose-6-phosphate glucose-1-phosphate (phosphoglucomutase) Glucose-1-phosphate + UTP UDP-glucose + PPi (UDP-glucose phosphorylase) PPi + H 2 O 2Pi (inorganic pyrophosphatase) UDP-glucose + glycogen (n) glycogen (n+1) + UDP (glycogen synthase) UDP + ATP UTP + ADP (nucleoside diphosphate kinase) Sum: Glc-6-P + ATP + glycogen (n) + H 2 O glycogen (n+1) + ADP + 2Pi