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BIOC 460 DR. TISCHLER LECTURE 31

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Aerobic metabolism. Figure 3. Pathway of glycogen synthesis (glycogenesis) Glucose ... Temporary weakness and cramping of muscle after exercise ... – PowerPoint PPT presentation

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Title: BIOC 460 DR. TISCHLER LECTURE 31


1
BIOC 460 - DR. TISCHLER LECTURE 31
GLYCOGEN METABOLISM PATHWAYS/ALLOSTERIC CONTROL
2
OBJECTIVES
  • Glycogenolysis Pathway
  • 1. general features describe glycogen
    phosphorylase.
  • 2. different fates of glucose-6-P from
    glycogenolysis in liver vs muscle
  • 3. Tense vs relaxed forms of glycogen
    phosphorylase activity
  • 4. Function of phosphorylase kinase in promoting
    glycogen mobilization relative to the
    phosphorylation state of glycogen phosphorylase.
  • 5. Explain the physiological basis for
  • a) AMP activating and ATP inhibiting glycogen
    phosphorylase
  • b) calcium activating phosphorylase kinase
  • G-6-P inhibiting phosphorylase/activating
    glycogen synthase
  • Why glycogen storage disease type I (von Gierke's
    disease) can lead to severe hypoglycemia but
    type V (McArdle's disease) does not cause
    hypoglycemia

3
  • Glycogenesis Pathway
  • 1. general features describe glycogen synthase
  • Carbohydrate loading
  • Explain the physiological basis for G-6-P
    activating glycogen synthase
  • 4. Compare two forms of glycogen synthase (d-form
    and i-form).

4
Figure 1. The glycogen structure showing the
glycosidic bonds
  • liver stores glycogen that provides 75 of
    glucose needed (mostly by RBC and brain) during
    first 24 hours of food deprivation
  • muscle stores glycogen solely for its own
    needs lack of G-6-Pase prevents formation and
    secretion of glucose for use by other tissues
  • highly branched structure to increase
    solubility provides many more sites for removal
    of glucose units that are phosphorylated by
    glycogen phosphorylase

5
Glycogen
LIVER PATHWAY
Pi
glycogen phosphorylase
Glucose-1-phosphate
phosphoglucomutase
glucose-6-phosphatase
Glucose-6-phosphate
Glucose
Pi
glycolysis
X
(inhibited by lack of fructose-2,6-bisP)
Figure 2a. Glycogenolysis and the fate of
glycogen in liver and kidney
6
Glycogen
MUSCLE PATHWAY
Pi
glycogen phosphorylase
Glucose-1-phosphate
phosphoglucomutase
Glucose-6-phosphate
glycolysis
Pyruvate
Figure 2b. Glycogenolysis and the fate of
glycogen in muscle.
7
Glucose
Figure 3. Pathway of glycogen synthesis
(glycogenesis)
8
activation by calcium inhibition by glucose-6-P
G-6-P ATP (in muscle)
Figure 4. Regulation of glycogen phosphorylase
9
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10
Figure 6. Regulation of glycogen synthase
11
GLYCOGEN STORAGE DISEASES
Type I Von Gierke Disease Hypoglycemia due to
defect of the final step of gluconeogenesis Decre
ased mobilization of glycogen produces
hepatomegaly.
Type V McArdle Disease Skeletal muscle
affected, but liver enzyme is normal No
hypoglycemia - muscle glycogen does not produce
glucose Temporary weakness and cramping of muscle
after exercise No rise in blood lactate during
strenuous exercise Muscle contains a high level
of glycogen
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