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GLYCOGENOLYSIS

Presentation By Sana Zahir

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GLYCOGENOLYSIS

• Glycogen Overview:

• Homopolysaccharide• Ready supply of glucose • Highly branched

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Glycogen Overview (cont):

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Glycogen Overview (cont):

• 2 Glycosidic Linkages: Linear linkage having (14) glycosidic bond = 90% Branched linkage having (16) glycosidic bond = 10%

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Glycogen Overview (cont):

2 GLYCOSIDIC LINKAGES

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Glycogen Overview (cont): Storage form of Glucose in

animals so also called as “animal starch”

Granular form High in liver (6-8%) and

muscles (1-2%)

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GLYCOGENOLYSIS:

"Degradtion Of Stored Glycogen Producing Free Glucose And Glucose 1 Phosphate"

Occurrence: Cytosole Triggered by low blood glucose

levels

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GLYCOGENOLYSIS (cont):

Enzymes Involved:

1.Glycogen Phosphorylase.2.Glycogen Debranching Enz;3.Phosphoglucomutase.

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GLYCOGENOLYSIS (cont):

1st Step: Phosphorolysis

Enzyme Involved: Glycogen phosphorylaseAction: Cleavage of α(1→4)linkagesPosition: non-reducing endsProduct: glucose-1-phosphate

BUTActivity of phosphorylase enzyme stops when it is 4 residue away from branched point.

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GLYCOGENOLYSIS (cont):

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GLYCOGENOLYSIS (cont):

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GLYCOGENOLYSIS (cont):

• Now Inorder To Rescue The Process, "DEBRANCHING ENZYME" Comes In Action

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GLYCOGENOLYSIS (cont):

• 2nd Step: Removal of Branches

General name Of Enzyme: Debranching enzyme Two enzymatic activities (Bifunctional enzyme)

1.Transferase Activity2.Glucosidase Activity

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GLYCOGENOLYSIS (cont):• Transferase activity:

Removes chain of 3 glucose residue from branch

Transfer them to the non-reducing end of linear glycogen chain

α-1,4 bond is broken and another α-1,4 bond is made.

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GLYCOGENOLYSIS (cont):

• Glucosidase Activity:

Breaks the α-1,6 bond at branch point Action is hydrolytically Releases a free glucose

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GLYCOGENOLYSIS (cont):

• Glycogen Debranching Enzyme:

-(1—>4) transglycosylase

Glucose-(1—>6) glucosidase

Limit Branch (4 residues)

(group transfer reaction)

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GLYCOGENOLYSIS (cont):

The remaining molecule of glycogen is again available for

the action of phosphorylase enzyme

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GLYCOGENOLYSIS (cont):

The third and last stage converts G1P (glucose-1-

phosphate) to G6P (glucose-6-phosphate) through the enzyme phosphoglucomutase.

G1P ↔ G6P

3rd step: formation of free glucose and glucose-6-phosphate

Catalysed By Phosphoglucomutase

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GLYCOGENOLYSIS (cont):

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GLYCOGENOLYSIS (cont):• FATES OF GLUCOSE 6

PHOSPHATE:

IN MUSCLES:This G6P can enter glycolysis and serve as an energy source to support muscle contraction.IN LIVER:It releases glucose into blood when blood glucose level drops.

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GLYCOGENOLYSIS (cont):

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GLYCOGENOLYSIS (cont):• Tissue which has Glucose 6 phosphatase can generate

free glucose.• LIVER KIDNEY INTESTINE HAVE THE ENZYME: The end product of glycogenolysis is free glucose

which entors to the blood stream • MUSCLES BRAIN AND ADIPOSE TISSUES DON'T

HAVE THE ENZYME: glycogen breakdown leads to the formation of glucose

6 phosphate which is then metabolized via glycolysis and TCA cycle

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GLYCOGENOLYSIS (cont):

glycogenolysis (1).mp4

• WATCH THIS VIDEO ANIMATION

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Thank you