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 + PPi (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 + H2O 2Pi (inorganic pyrophosphatase)

UDP-glucose + glycogen (n) glycogen (n+1) + UDP (glycogensynthase)

UDP + ATP UTP + ADP (nucleoside diphosphate kinase)

Sum: Glc-6-P + ATP + glycogen (n) + H2O glycogen (n+1) + ADP + 2Pi