what is glycogen
- homo-polymer of glucose
- rapidly mobilized storage form of glucose
function of glycogen
maintain glucose homeostasis
glucose is imp because
- main energy source:brain and RBC
- modify lips
- for PPP
where do we get glucose
- glycogen and fasting
- GNG during prolonged fasting
what is the locatioin of the glucogen?
- in the cytosol in cytosolic granuels
- skeletal muscle
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
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
what is the nonreducing end
- without the aldhyde group
- this is where glucoses are added and removed
what is the reducing end
the end of the glycogen with the aldehyde
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)
what are the steps in glycogen degradation ?
Glycogen> Glucose ( via glycogen phosphorylase + debranching enzyme)> G1P > G6P ( via phosphoglucomutase) >Glucose ( G6Phosphatase)
synthesis of glycogen
what does UTP do to glucose?
it activates it so that it can link to other glucose to make glycogen
steps of glycogenesis
Glucose 6 phosphate > G1P(via phosphoglucomutase)>UDP glucose ( via UDP glucose pyrophosphorylase)> Glycogen (via glycogen synthase)
what is necessary for glycogen synthase to wokr?
- oligosaccharide primer
how do the primers of Glycogen synthesis form ?
through glucose autoglycosylation activity a tyrosine residue is added.
what is glycogenin
enzyme and scaffold, extending the carbohydrate chain up to 8 glucose oligomer using UDP-glucose donor
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 )
why go glycogen branch?
- more soluble
- creates a large # of non-reducing ends which increases the rate or synthesis and degradation
function og glycogen synthase
transfer glucose from UDP glucose to the non reducing end
Break down of glycogen
difference btw liver and muscle
liver can push out glucose but muscles cannot.
1-3% of glycogen is continuosly degraded by the lysosomal enzyme a-1,4 glucosidase
- 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
epinephrine and Glucagen both do what to glycogen
trigger glycogen breakdown
generally speaking insulin activates
generally speaking glycogenand epinephrine activates
Von Gierke Disease Type Ia and I1
glucose cannot be released in the blood and accumulates in liver and kidney
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
the deb ranching enzyme is defective
what is the process of changing fructose into glucose
fructokinase and aldolase B triose kinase which results in glyceraldehyde 3 phosphate.
what is fructosuria
fructose kinase deficency
Hereidtary fructose intolerance ( HFI)
aldolas B deficency resuling in decrease in cellular interstital phosphate and ATP
what is sorbitol
an alcohol form of glucose
what is the glycogen phospgorylase
this phosporylates the phosphorylase kinase
what enzyme converts glucose to sorbital