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How is excesses Glucose stored?
As glycogen in animals/starch in plants
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Most common tissues for Glycogen synthesis/storage
- Liver and Skeletal Muscle
- Muscles use it in glycolysis for ATP
- Liver breaks it down to glucose and sends it where it is needed
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How is Glycogen stored in blood stream?
In glycogen granules, which also contain tools for making/breaking glycogen
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Structure of Glycogen
- Glucose residues bound together in alpha-1,4-glycosidic bonds.
- Branched points are alpha-1,6-glycosidic bonds
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Degradation of Glycogen
Glucosen+1 + Pi --> Glucosen + G-1-P
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Glycogen Synthesis
Glucosen + UDP-glucose --> Glucosen+1 + UDP
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Glycogen Phosphorylase
Pops a glucose off with an added Pi on it
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Glycogen Transferase
Moves chain from branches side chain to main chain
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alpha-1->6 Glycosidase
Takes the branch bounded glucose and removes it
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Regulation of Glycogen Phosphorylase (a)
- Glucagon signals phosphorylase b kinase to phosphorylate phosphorylase a making it more active
- -epinephrine, Ca2+, AMP all also raise it
- Phosphorylase a phosphatase dephosphorylates making less active
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Glucose-6-Phosphatase
- In liver/Kidney
- Not in muscle/adipose
- Needed to secrete glucose
- Defines role for glycogen in liver/muscle
- Used in Bypass step 3 of gluconeogenesis
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Where does Glucose-6-Phosphate turn G6P to Glucose and Pi
ER Lumen, then ported out into blood via GLUT2
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4 Stages of Glycogen Synthesis
- -Conversion of G6P to G1P by phosphoglucomutase
- -Glucose phosphate is converted to UDP-glucose by UDP-glucose pyrophosphorylase
- -UDP-glucose adds itself to glucose chain in glycogen
- -Make branches with glycosyl-4:6 transferase
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Activation of G-1-P for Glycogen synthesis
G-1-P + UTP --> UDP-glucose + PPi
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Plant Starches
- Amylose: Not branched
- Amylopectin: Branched like glycogen, less frequent
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