Biochemistry- Carbohydrate metabolism Steps on breakdown of glycogen

1. GLYCOGENOLYSIS
CARBOHYDRATE METABOLISM

2. ABOUT GLYCOGEN
• Homo-polysaccharide
• Highly branched
• Storage form of carbohydrate

3. Glycogenolysis
• Degradation of stored glucose
• Triggered by low blood glucose levels
can do so anaerobically
Or during a muscular exercise
when an organism needs energy quickly
Why does this pathway occur?

4. • Site:
• Organ: liver& muscle
• Organelle: cytoplasm,
lysosomes, SER
• RATE LIMITING
STEP: Glycogen
phosphorylase,
( coenzyme= pyridoxal
phosphate)

5. REACTIONS/STEPS
Action of glycogen phosphorylase
Removal of branches
Conversion of glucose-1-PO4 to glucose

6. ACTION OF GLYCOGEN
PHOSPHORYLASE

7. About glycogen phosphorylase
• It contains PLP as prosthetic group.
• The alpha-1,4 linkages in the glycogen are cleaved.
• It removes glucose units at one time.
• If glycogen phosphorylase alone acts on a glycogen molecule, the final
product is a highly branched molecule; it is called limit dextran.
• Glycogen phosphorylase breaks α-1,4 linkages and de-branching enzyme
breaks α-1,6 linkages to release single units of glucose-1- phosphate.

8. Removal of branches
• Debranching enzyme= Bifunctional enzyme
alpha 1,4 1,4 glucan
transferase
Alpha 1,6 Glucosidase/
Amylo 1,6 glucosidase

11. Conversion of Glucose 1 PO4 to glucose
• In LIVER
Glucose 1 PO4
Glucose 6 PO4
Glucose
Phosphoglucomutase
Glucose 6 phosphataseH2O
Pi
• In MUSCLE
Glucose 1 PO4
Glucose 6 PO4
Anaerobic glycolysis
Pyruvate Lactate
Phosphoglucomutase
Absence of glucose 6
phosphatase in muscle
Energetics= Energy yield from one glucose residue derived from glycogen is
3 ATP molecules.

12. Enzymes in conversion
• Phosphoglucomutase
• converts glucose- 1-phosphate to glucose-6-phosphate, which is then shuttled into
the glycolytic pathway.
• Glucose 6 phosphatase
• Present in liver
• Absent in muscle
• Present in cytoplasm of SER
• It is common to gluconeogenesis and glycogenolysis

13. SIGNIFICANCE
• Glycogenolysis plays an important role in the fight-or-flight response.
• It contributes to the regulation of glucose levels in the blood.
• The metabolism of glycogen polymers becomes important during fasting.
• In myocytes (muscle cells), glycogen degradation serves to provide an immediate
source of glucose-6-phosphate for glycolysis, to provide energy for muscle
contraction.
• In hepatocytes, the main purpose of the breakdown of glycogen is for the
release of glucose into the bloodstream for uptake by other cells.