CHAPTER 18: METABOLISM OF GLYCOGEN
Structure of Glycogen
•Glycogen, the storage form of glucose, is a branched
glucose polysaccharide composed of chains of glucosyl
units linked by -1,4 bonds with -1,6 branches every 8 to
10 residues
•
Function of glycogen in skeletal muscle and liver
•degraded mainly to glucose 1-phosphate,which is
converted to glucose 6-phosphate. In skeletal muscle
and other cell types, the glucose 6-phosphate enters the
glycolytic pathway
Skeletal Muscle
•important fuel source for skeletal muscle when ATP
demands are high and when glucose 6-phosphate is
used rapidly in anaerobic glycolysis
•emergency fuel source that supplies glucose for the
generation of ATP in the absence of oxygen or during
restricted blood flow
Liver
•first and immediate source of glucose for the
maintenance of blood glucose levels
•the glucose 6-phosphate that is generated from
glycogen degradation is hydrolyzed to glucose by
glucose 6-phosphatase, an enzyme present only in the
liver and kidneys
•Glycogen degradation thus provides a readily mobilized
source of blood glucose as dietary glucose decreases,or
as exercise increases the utilization of blood glucose by
muscles
The pathways of glycogenolysis and gluconeogenesis in the liver
both supply blood glucose, and, consequently, these two
pathways are activated together by glucagon. Gluconeogenesis,
the synthesis of glucose from amino acids and other
gluconeogenic precursors, also forms glucose 6-phosphate,so
that glucose 6-phosphatase serves as a “gateway”to the blood for
both pathways
Glycogen Synthesis
Glycogen breakdown
Glycogen Storage Diseases
Regulation of Liver and Muscle Glycogen Stores
Disorders of Glycogen Metabolism
