2. Glycogen Metabolism (Glycogenesis)

3. Learning Objectives To learn about the storage form of Glucose
To describe how glucose is converted into its storage form i.e. Glycogen
To discuss the regulation of this process

4. Glycogen Also known as Animal Starch
Storage form of glucose (liver & muscle)
Readily available source of hexose units.
Average glycogen molecule contains ,000 – 60,000 glucose molecules.

5. Glycogen
Glycogen is stored in the cytosol & endoplasmic reticulum as granules (-particles) (as in muscles).
Each -particle is an individual glycogen molecule.
-particles aggregate to form a larger particle (-particle) (as in liver)
Storage granules contain enzymes both for
glycogenesis and glycogenolysis

6. Glycogen
Liver Glycogen: (Up to 6%  70-80g) is used to maintain the blood glucose level between meals.
After hours fasting, liver is depleted of glycogen.

7. Glycogen
Muscle Glycogen: (Up to 1%  250g) is used as source of glucose for muscle itself, and cannot directly contribute to blood glucose level.

8. Metabolism of Glycogen
Two processes
Glycogenesis
Synthesis of glycogen from glucose
Glycogenolysis
Breakdown / degradation of glycogen into glucose
Both processes are separate metabolic pathways having only one enzyme in common namely, phosphoglucomutase
Both these processes are reciprocally regulated
Site – liver, muscle (cytosol)

9. Metabolism of Glycogen
Glycogen Storage Diseases (Glycogenoses):
Inherited disorders due to deficiency or absence of enzyme(s) involved in glycogenesis or glycogenolysis – leading to deficient metabolism or deposition of abnormal form of glycogen  muscular weakness  even death.

10. Glycogenesis Requirements Glucose molecules
Glycogen primer and glycogenin
Enzymes
ATP, UTP & Mg++
Glycogen Primer
Synthesized by glycosylation (by UDPGlc) of tyrosine residue on the backbone of protein primer, glycogenin.

11. Reactions of Glycogenesis

13. Also known as Amylo [1 4]  [1 6]-transglucosidase