Glycogen Metabolism

10 vocabulary flashcards covering the main molecules, enzymes, and bond types involved in glycogen synthesis and breakdown.

Glycogen

Highly branched polymeric storage form of glucose in animals; located in muscle (breakdown yields glucose for muscle contractions) and liver (maintains BG homeostasis)

Glycogen granules

Have many tiers of branched chains of D-glucose

Glycogen Synthase

Enzyme that adds glucose from UDP-glucose to nonreducing end of glycogen chain with n>4 residues, excluding UDP; requires glycogenin as a priming enzyme

Glycogen Branching Enzyme

Enzyme that creates α1,6-glycosidic linkages found at glycogen branch points

Glycogen Phosphorylase

Catalyzes cleavage at the nonreducing ends of glycogen chains, releasing G1Ps that can be converted to G6Ps; acts repetitively until it reaches a point 4 residues away from a (a1→6) branch point

Debranching Enzyme

transfers branches onto main chains and releases the residue at the (a1→6) branch as free glucose

UDP-Glucose

Activated glucose donor produced from NTP and a sugar phosphate via NDP-sugar pyrophosphorylase

sources of G6P

hexokinase isozymes derive G6P from glucose; lactate taken up by liver is converted to G6P via gluconeogenesis

rxn of glycogen synthase

autocatalytic formation of a glycosidic bond between the glucose of UDP-glucose and Tyr of glycogenin. then, seven (or more) more glucose residues from UDP-glucose are added to form a primer that can be acted on by glycogen synthase

fates of G6P

skeletal muscle: enters glycolysis; liver: converted to glucose in ER for export to blood