glycogen metabolism pathways

1. NAME:RUDRADEEP HAZRA
STREAM-BACHELOR OF PHARMACY
(2ND SEM)
ROLL NO -19301918060.
Glycogen Metabolism
Pathways.

2. Glycogen-Introduction
 Glycogen is a readily mobilized storage form of glucose.
 It is a very large, branched polymer of glucose residues
that can be broken down to yield glucose molecules when
energy is needed.
 Most of the glucose residues in glycogen are linked by α-
1,4-glycosidic bonds.
 Branches at about every tenth residue are created by α-
1,6-glycosidic bonds.

3. Glycogen storage sites
 It is stored mainly in liver and muscle.
 The liver content of glycogen is greater than that of
muscle.
 Since, the muscle mass of the body is considerably
greater than that of the liver, about three-quarters of
total body glycogen is in muscle.

4. Glycogenolysis
 The degradation of stored glycogen to produce
glucose is called glycogenolysis.
 The pathways for the synthesis and degradation of
glycogen are not reversible.
 An independent set of enzymes present in the cytosol
carry out glycogenolysis. Glycogen is degraded by
breaking alpha -1,4 – and alpha -1,6- glycosidic
bonds.

5. Steps of Glycogenolysis
 The glucose units of the outer branches of glycogen
enter the glycolytic pathway through the action of
three enzymes: glycogen phosphorylase,glycogen
debranching enzyme, and phosphoglucomutase.
 Glycogen phosphorylase catalyzes the reaction in
which an (α 1-4) glycosidic linkage between two
glucose residues at a nonreducing end of glycogen
undergoes attack by inorganic phosphate (Pi),
removing the terminal glucose residue as -D-glucose
1-phosphate.

6. Action of debranching enzymes
Transferase and Debranching enzyme-
 The Transferase shifts a block of three glucosyl
residues from one outer branch to the other.
 This transfer exposes a single glucose residue joined
by an α -1,6-glycosidic linkage.
 α-1,6-Glucosidase, also known as the debranching
enzyme, hydrolyzes the α -1, 6glycosidic bond,
resulting in the release of a free glucose molecule.

7. Glucose -6- Phosphate to Glucose
Phosphoglucomutase-
 Glucose 1-phosphate formed in the phosphoroylytic
cleavage of glycogen must be converted into glucose
6-phosphate to enter the metabolic mainstream. This
shift of a phosphoryl group is catalyzed by
Phosphoglucomutase.

8. Glycogen Degradation to Glucose

9. Glycogen Metabolism
 Glycogen represents the principal storage form of
carbohydrate in the body, mainly in the liver and muscle.
 It is broken down by a separate pathway- glycogenolysis.
 Glycogenolysis leads to glucose formation in liver and lactate
formation in muscle owing to the respective presence or
absence of glucose 6-phosphatase.
 Cyclic AMP integrates the regulation of glycogenolysis and
glycogenesis by promoting the simultaneous activation of
phosphorylase and inhibition of glycogen synthase.
 Insulin acts reciprocally by inhibiting glycogenolysis and
stimulating glycogenesis.
 Inherited deficiencies in specific enzymes of glycogen
metabolism in both liver and muscle are the causes of
glycogen storage diseases.

10. Conclusion
 I am very much thankful to my professor to give me
such a wonderful topic to work on.
 Reference –Internet,biochemistry book by
satyanarayana and principles of biochemistry by
A.Leningher.