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what is glycogen
- homo-polymer of glucose
- rapidly mobilized storage form of glucose
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function of glycogen
maintain glucose homeostasis
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glucose is imp because
- main energy source:brain and RBC
- modify lips
- for PPP
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where do we get glucose
- meals
- glycogen and fasting
- GNG during prolonged fasting
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what is the locatioin of the glucogen?
- in the cytosol in cytosolic granuels
- liver
- skeletal muscle
- kidney
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what is the structure of glycogen
- glycogen has many branches
- a-1,4 linkages 9 main chain) with a-1,6 at the branching sites
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what does alpha-1,4 linkage mean?
- the hydroxy on the anomeric is linked to the C4
- a carbon is point downward alpha mean that the carbon is point downwards
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what is the nonreducing end
- without the aldhyde group
- this is where glucoses are added and removed
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what is the reducing end
the end of the glycogen with the aldehyde
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what are the steps in glycogen synthesis ?
Glucose>G6P9 ( via hexokinase or glucokinase ) >G1P ( via phosphoglucomustase)>UDPG (via UDG-glucose pyrophosphorylase ) >glycogen ( via transferase, synthase and glycogen primer)
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what are the steps in glycogen degradation ?
Glycogen> Glucose ( via glycogen phosphorylase + debranching enzyme)> G1P > G6P ( via phosphoglucomutase) >Glucose ( G6Phosphatase)
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synthesis of glycogen
glycogenesis
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what does UTP do to glucose?
it activates it so that it can link to other glucose to make glycogen
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steps of glycogenesis
Glucose 6 phosphate > G1P(via phosphoglucomutase)>UDP glucose ( via UDP glucose pyrophosphorylase)> Glycogen (via glycogen synthase)
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what is necessary for glycogen synthase to wokr?
- oligosaccharide primer
- glycogenin
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how do the primers of Glycogen synthesis form ?
through glucose autoglycosylation activity a tyrosine residue is added.
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what is glycogenin
enzyme and scaffold, extending the carbohydrate chain up to 8 glucose oligomer using UDP-glucose donor
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how does the branching enzyme work for elongation ?
it removes a 6 to 8 oligomer from non reducing end and attached it by a-1,6 linakage ( at least 4 residues from a branch point )
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why go glycogen branch?
- more soluble
- creates a large # of non-reducing ends which increases the rate or synthesis and degradation
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function og glycogen synthase
transfer glucose from UDP glucose to the non reducing end
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Break down of glycogen
glycogenolysis
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difference btw liver and muscle
liver can push out glucose but muscles cannot.
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lysosomal degradation
1-3% of glycogen is continuosly degraded by the lysosomal enzyme a-1,4 glucosidase
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Pompe disease
- Type II glycogen storage disease
- deficiency of the lysosomal alpha- 1,4glucosidase
- causing the build up of glycogen and impariment of normal functioning of organ especially heart
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epinephrine and Glucagen both do what to glycogen
trigger glycogen breakdown
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generally speaking insulin activates
phosphatatase
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generally speaking glycogenand epinephrine activates
Kinase
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Von Gierke Disease Type Ia and I1
glucose cannot be released in the blood and accumulates in liver and kidney
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what is the difference between Von Gierke Disease Type Ia and Ib
- type Ia is deficiency in Glucose 6 phosphatase
- Type Ib is deficency in glucose 6 phosphate translocase
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Cori disease
the deb ranching enzyme is defective
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what is the process of changing fructose into glucose
fructokinase and aldolase B triose kinase which results in glyceraldehyde 3 phosphate.
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what is fructosuria
fructose kinase deficency
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Hereidtary fructose intolerance ( HFI)
aldolas B deficency resuling in decrease in cellular interstital phosphate and ATP
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what is sorbitol
an alcohol form of glucose
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what is the glycogen phospgorylase
this phosporylates the phosphorylase kinase
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what enzyme converts glucose to sorbital
aldose reductase
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