Glycogen Metabolism - JU Medicine...Sources of Blood Glucose •Diet –Starch, mono and...
Transcript of Glycogen Metabolism - JU Medicine...Sources of Blood Glucose •Diet –Starch, mono and...
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Glycogen Metabolism
Suggested Reading:
Lippincott’s Ilustrated reviews: Biochemistry
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Sources of Blood Glucose
• Diet– Starch, mono and disahccarides, glucose – Sporadic, depend on diet,
• Gluconeogenesis– Sustained synthesis– Slow in responding to falling blood glucose level
• Glycogen – Storage form of glucose– Rapid response and mobilization. – Limited amount– Important energy source for exercising muscle.
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* Extensively branched homopolysaccharide
* One molecule consists of hundreds of thousands of glucose units- up to M.W. of 100,000,000.
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Reducing end
Nonreducingend
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Degradation of glycogen
Degradation of glycogenOne glucose unit is removed at a time
From the nonreducingends
Released in the form of glucose 1-phosphate
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Phosphate Ribose Uracil
Glycogen is synthesized by adding glucose one by oneUDP-Glucose s the active donor of glucose units
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Formation of UDP-Glucose
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Formation of UDP-Glucose
Glucose- P P P P
Ribose-Uracil
Glucose- P P
Ribose-Uracil
P P
Pyrophosphate
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Glycogen Storage Diseases
• Genetic diseases
• Defect in an enzyme required for synthesis or degradation ➔
• Accumulation of excessive amount of glygcogen
• In one or more tissue
• Severity: FATAL in Infancy……. Mild disorder
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Glycogen Storage Diseases (examples)
• I Glucose-6-phosphatase (von Gierk’s) disease
– Liver, kidney and intestine.
– Severe fasting hypoglycemia
– Hepatomegaly fatty liver.
– Normal glycogen structure.
– Progressive renal disease.
– Growth retardation.
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Glycogen Storage Diseases (examples)
• V Muscle glycogen phosphorylase (McArdle syndrome)
– Only muscle is affected;
– Weakness and cramping of muscle after exercise
– no increase in [lactate] during exercise
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Glycogen Storage Diseases (examples)• II Lysosomes α (1→4) glucosidase ➔ POMP Disease
• Degradation of glycogen in the lysosomes
• ≈ 3% of glycogen is degraded in the lysosomes
• Affects liver, heart and muscle
• Excessive glycogen in abnormal vacuoles in the lysosomes
• Massive cardiomegaly
• Normal blood sugar, normal glycogen structre
• Early death from heart failure.
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Energy needed for glycogen synthesis
Glucose + ATP Glucose 6-phosphate + ADP
Glucose 6-phosphate Glucose 1-phosphate
Glucose 1-phosphate UTP UDP-Glucose PPi
PPi + H2O 2Pi
UDP-Glucose + Glycogen(n) UDP + Glycogen(n+1)
Glc. + ATP + UTP+Glycogen(n) ADP + UDP +Glycogen(n+1
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The net reaction in glycogen synthesis and degradation
Glucose 1-phosphate + UTP UDP-Glucose + PPi
PPi + H2O 2Pi
UDP-Glucose + Glycogen(n) UDP + Glycogen(n+1)
Glc. 1-phosph. + UTP+Glycogen(n) UDP +Glycogen(n+1
Degradation
Glycogen(n) + Pi Glycogen(n-1) +Glc. 1-phosphate
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Allosteric RegulationRapid response to cell’s needsAvailable substate and ATP➔
synthesis
↓↓Glucose and ↓ATP ➔Glycogenolysis
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PInhibitor protein
Glc
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GLYCOGEN SYNTHESIS IS INHIBITED
cAMP dependent protein kinase A
Phosphorylation at several sites
Inhibition is proportional to the degree of phosphorylation
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Ca2+-calmodulin activates dephosphorylated Phosphorylase kinase
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Calcium Activation of liver phosphorylase Kinase
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Next TopicMetabolism of mono and
disaccharides
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Uracil
Ribose
Phosphate
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