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22 Cards in this Set
- Front
- Back
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Glycogen
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Branched glucose homopolymer
1-2% in muscle and <10% in liver |
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Why glycogen (instead of fat) as energy storage?
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-Rapid utilization of glycogen in muscle
-Aerobic metabolism of fat -Fatty acids cannot be converted to glucose in animal cells |
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Enzymes for the glycogen breakdown
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-Glycogen phosphorylase (or phosphorylase)
-Glycogen debranching enzyme -Phosphoglucomutase |
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G-1-P ---> G-6-P
enzyme? |
Phosphoglucomutase
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Glycogen (n-residues) + Pi ---->
Glycogen (n-1 residues) + G-1-P enzyme? |
Glycogen phosphorylase
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Glycogen phosphorylase
Allosteric regulation: |
(-) ATP, G6P, and glucose
(+) AMP |
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Enzymes for the glycogen synthesis:
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Glycogenin
UDP-glucose pyrophosphorylase Glycogen synthase Glycogen branching enzymes |
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G-1-P + UTP ----> UDP-glucose + 2Pi
enzyme? |
UDP-glucose pyrophosphorylase
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UDP-glucose + glycogen (n residues) <-----> UDP + glycogen (n+1 residues)
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Glycogen synthase
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Regulation of glycogen synthase
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Allosteric regulation:
(-) AMP (+) G6P, ATP Covalent modification (phosphorylation) -Dephosphoenzyme: glycogen synthase a (more active) -Phosphoenzyme: glycogen synthase b (less active) |
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Control of glycogen metabolism
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-Allosteric control of glycogen phosphorylase and glycogen synthase
-Enzymatic phosphorylation cascades: Phosphorylation activates glycogen phosphorylase Phosphorylation inactivates glycogen synthase -Hormonal effects: Glucagon and epinephrine: (+) glycogen degradation Insulin: (-) glycogen synthesis |
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Covalent modification of glycogen phosphorylase:
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-The modified (m, phosphorylated) form is active (a form)
-The original (o, desphosphorylated) form is inactive (b form) |
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Two enzymes each of which activates the glycogen breakdown by binding to either intracellular calcium or cAMP:
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-Phosphorylase kinase
-Protein kinase A |
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Second messenger that activates protein kinase A:
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cAMP
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Second messenger that activates phosphorylase kinase
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Ca+2
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Two hormones that activate glycogen breakdown
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Glucagon and epinephrine
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Phosphorylase kinase
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-Four nonidentical subunits
-One catalytic (delta) and three regulatory subunits -Activated by Ca+2 binding to delta subunit (calmodulin) and phosphorylation of alpha and beta subunits by protein kinase A. |
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Calmodulin (CaM)
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Ubiquitous Ca+2 binding protein
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cAMP is generated by ______
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adenylate cyclase
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cAMP is an activator of _______
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protein kinase A (PKA)
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Covalent control of glycogen synthase
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-The modified (m, phosphorylated) form is inactive (b form)
-The original (o, desphosphorylated) form is active (the a form) -Phosphorylase kinase and other kinases phosphorylate and thereby inactivate glycogen synthase |
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Receptor only in the liver but not in muscle cells
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Glucagon receptor
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