Glycogen Synthesis, Degradation and Hormonal Control

WHAT IS GLYCOGEN

branched polysaccharide that serves as the primary stored form of glucose in animals, fungi, and bacteria.

Where is glycogen found?

found as granules in the cytosol

Muscles have lowest conc

Hepatocyte(liver) have highest concentration

Glycogen Granule Structure

inner: gamma particles → protein rich subunits

middle: beta subunits → carbohydrate polymer and bound gamma particles (faster E source)

outer: alpha subunits → composed of beta subunits rich in disulfide bonds

Glycogenin GN

Dimer (weak binding)

1. intermolecular glycosylation - transfer of 1-2 glucose to Tyr-194 from partner GN

2. intramolecular glycosylation - elongation of a primer chain (7-16 glucose residues)

binds to ACTIN FILAMENTS for the start of glycogen synthesis

Glycogen Synthase(GS)

elongation of primer chain through a-1,4-linkage

Glycogen-branching enzyme(GBE)

adds glucose residues to the granule through a-1,6-linkage

Why is glycogen so highly branched?

makes it more souble

fast synthesis/degradation

Glycogenesis steps

1. Glucokinase (Hexokinase IV)

2. Phosphoglucomutase

3. UDP-GLucose Phosporylase

4. Glycogenin

5. Glycogen Synthase

6. Glycogen Branching Enzyme

Phosphoglucomutase

Does not use ATP

must convert Glucose 1 → glucose 6 before it can enter glycolysis

UDP-Glucose

the donor of glucose in the formation of glycogen

Glycogenin

protein homodimer that funcation as a primer

forms a tight 1:1 complex with glycogen synthase

Glycogen synthesis elongation and branching

Glycogenolysis 3 steps

Glycogen phosphorylase

catalyzes the phosphorolysis of glucose units from glycogen

does not use ATP

Three “fates” of Glucose 6 Phosphatase

1. initial substrate for glycolysis

2. processed by the pentose phosphate pathway to yield NADPH and ribose derivitaves

3. converted into free glucose for release into the bloodstream

Allosteric Glycogen synthesis/degradation in the liver

Hormonal Glycogen synthesis/degradation in the liver

Glucagon from alpha cells in pancreas cells and requires epinephine(adrenlinine)

i lowkey think this is like fight or flight signal in the liver like adrelinin make glycolysis happen quick and fast

Hormonal Regulation of glycogenin synthesis

hormonal regulation of glycogen degradation by epinphrin and ca2+

adrenalin (ehifiebjkl) can bing alpha or beta adrenergic receptors

Allosteric Regulation what does Liver use?

Glucose

Allosteric Regulation what does muscle use?

AMP

Activation of muscle glycogen phosporlyase during exercise

Glycogenolysis good for newborns

glycogen accumlates in the fetal liver alot before birth.

the activity of glycogen synthase increase but glycogen phosporylase remains low just prior to term