Glycogen: Structure, Metabolism & Pharmacology
🧬 Glycogen: Structure, Metabolism & Pharmacology
A comprehensive review for Pharmacy Students regarding carbohydrate storage, regulation, and associated pathologies.
01 Structure & Function
Definition: Glycogen is a multibranched polysaccharide of glucose that serves as a form of energy storage in animals, fungi, and bacteria. It is the primary storage form of glucose.
- ● Linkages: Linear chains via α-(1,4) glycosidic bonds.
- ● Branching: Occurs every 8-12 residues via α-(1,6) glycosidic bonds.
Liver Glycogen (~100g)
Function: Maintains blood glucose levels during fasting.
Enzyme: Contains Glucose-6-Phosphatase (allows glucose release into blood).
Muscle Glycogen (~400g)
Function: Fuel reserve for muscle contraction (ATP generation).
Enzyme: Lacks Glucose-6-Phosphatase (glucose stays in muscle).
02 Metabolism Pathways
| Pathway | Rate Limiting Enzyme | Key Regulator | Purpose |
|---|---|---|---|
| Glycogenesis | Glycogen Synthase | Activated by Insulin Inhibited by Glucagon/Epi |
Storage (Fed State) |
| Glycogenolysis | Glycogen Phosphorylase | Activated by Glucagon/Epi Inhibited by Insulin |
Release (Fasting/Stress) |
03 Clinical Relevance: GSDs
Type I (Von Gierke)
SevereDefect: Glucose-6-phosphatase.
Symptoms: Severe fasting hypoglycemia, hepatomegaly, hyperuricemia.
Type II (Pompe)
LysosomalDefect: Lysosomal α-1,4-glucosidase.
Symptoms: Cardiomegaly, muscle weakness, early death.
Type III (Cori)
StructureDefect: Debranching enzyme.
Symptoms: Milder hypoglycemia, normal blood lactate.
Type V (McArdle)
MuscleDefect: Muscle glycogen phosphorylase.
Symptoms: Exercise intolerance, myoglobinuria.
Pharmacy Clinical Pearl
Diabetes Management: Metformin exerts part of its effect by inhibiting hepatic gluconeogenesis and glycogenolysis.
Corticosteroids: Promote glycogen storage in the liver but create insulin resistance, leading to steroid-induced hyperglycemia.