GIS Sheet 1 – Glycogen Storage Diseases Notes
Chemical structure and function of glycogen:
- (C6H10O5)n
- The reactions creating these linkages
in glycogen synthesis are catalysed by
glycogen synthase and de-branching
enzyme.
- Glycogen is a branched polymer of linear glucose residues joined
together by a(1, 4) and a(1, 6) glyosidic linkages. It is a polysaccharide
- Glycogen acts as a secondary long-term storage of glucose.
- Storage of glucose is 200g in liver.
Physiological function of Glycogen in liver and muscles:
Liver: Glycogen maintains blood glucose. Liver converts glycogen glucose in
response to low blood sugar levels. Glucose increases blood sugar levels to
normal
Muscle: Glycogen is glucose and is used an energy source for muscle activity.
Useful for sudden, strenuous activity. Energy is more efficient when stored in
form of fat.
Function of Glycogen Phosphorylase:
- Is a monomer enzyme responsible for breaking α(1, 4) linkages in
glycogen
- Uses inorganic HPO42- to split glucose from polysaccharide chains of
glycogen by releasing glucose-1-phosphate
The difference in activity of glycogen phosphorylase vs amylase:
- Glycogen Phosphorylase uses phosphorolysis to cleave linkages α(1, 4)
- Amylase uses hydrolysis to clave linkages α(1, 4)
Function of De-Branching Enzyme:
- Facilitates the breakdown/hydrolysis of glycogen- breaks the α(1, 6)
linkages. This is because α(1, 6) glyosidic bonds are not susceptible to
cleavage by phosphorylase.
- When phosphorylase reaches 4 residues from branching point it stops
cleaving and debranching enzyme performs Glycosyltransferase +
Glucosidase before phosphorylase can continue.
Chemical structure and function of glycogen:
- (C6H10O5)n
- The reactions creating these linkages
in glycogen synthesis are catalysed by
glycogen synthase and de-branching
enzyme.
- Glycogen is a branched polymer of linear glucose residues joined
together by a(1, 4) and a(1, 6) glyosidic linkages. It is a polysaccharide
- Glycogen acts as a secondary long-term storage of glucose.
- Storage of glucose is 200g in liver.
Physiological function of Glycogen in liver and muscles:
Liver: Glycogen maintains blood glucose. Liver converts glycogen glucose in
response to low blood sugar levels. Glucose increases blood sugar levels to
normal
Muscle: Glycogen is glucose and is used an energy source for muscle activity.
Useful for sudden, strenuous activity. Energy is more efficient when stored in
form of fat.
Function of Glycogen Phosphorylase:
- Is a monomer enzyme responsible for breaking α(1, 4) linkages in
glycogen
- Uses inorganic HPO42- to split glucose from polysaccharide chains of
glycogen by releasing glucose-1-phosphate
The difference in activity of glycogen phosphorylase vs amylase:
- Glycogen Phosphorylase uses phosphorolysis to cleave linkages α(1, 4)
- Amylase uses hydrolysis to clave linkages α(1, 4)
Function of De-Branching Enzyme:
- Facilitates the breakdown/hydrolysis of glycogen- breaks the α(1, 6)
linkages. This is because α(1, 6) glyosidic bonds are not susceptible to
cleavage by phosphorylase.
- When phosphorylase reaches 4 residues from branching point it stops
cleaving and debranching enzyme performs Glycosyltransferase +
Glucosidase before phosphorylase can continue.
