Download Glycogen Metabolism-1 (Glycogenesis)

Glycogen Metabolism
(Glycogenesis)
Learning Objectives

To learn about the storage form of Glucose
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To describe how glucose is converted into its
storage form i.e. Glycogen

To discuss the regulation of this process
Glycogen

Also known as Animal Starch

Storage form of glucose (liver & muscle)

Readily available source of hexose units.

Average glycogen molecule contains
10,000 – 60,000 glucose molecules.
Glycogen



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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
Glycogen
Liver Glycogen:
(Up to 6%  70-80g) is used to
maintain the blood glucose level
between meals.
After 12-18 hours fasting, liver is depleted of glycogen.
Glycogen
Muscle Glycogen:
(Up to 1%  250g) is used as
source of glucose for
muscle
itself, and cannot
directly
contribute to blood
glucose level.
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)
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.
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.
Reactions of
Glycogenesis
Also known as Amylo [1 4]  [1 6]-transglucosidase