glycogen metabolism reducing end. glycogen metabolism glycogen breakdown (glycogenolysis) and...
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Glycogen Metabolism
Reducing end
Glycogen MetabolismGlycogen Breakdown (Glycogenolysis) and Glycogen SynthesisWhy breakdown glycogen and not lipid to produce glc?1. Mobilized faster2. Can be metabolized anaerobically
Glycogen breakdownGlc units are removed one at a time from the nonreducing ends by phosphorolysis
Glycogen MetabolismGlycogen BreakdownRemove all the 14 branches and an additional enzyme is rec’d to remove 16
Glycogen MetabolismGlycogen Breakdown - Glycogen phosphorylaseFirst known example of an allosterically regulated enzymeFirst enzyme shown to be controlled by reversible phosphorylation
In muscle:
Resting muscle
During vigorous muscular activity, epinephrine triggers phos
Triggers glycogen breakdown
Glycogen MetabolismGlycogen Breakdown - Glycogen phosphorylaseIn liver:
Low blood sugar - glucagon activates phosphorylase b kinase, initiates release of glc into blood
phosphorylase kinase
Glycogen MetabolismGlycogen Breakdown Fate of glucose 1-phosphateMuscle / liver phosphoglucomutase
G1P G6P Glycolysis
If you just need glucose:LiverGluconeogenesis or glucose 6-phosphatase
Glycogen G1P G6P + H2O Glc + Pi
In brain & muscle:No gluconeogenesis and no glucose 6-phosphatase soget glc from gluconeogenesis in liver or from injested glc, both of which get delivered through bloodstream
In liver, glycogen is a reservoir of glc, converted into blood glc that moves to other tissues
In muscle, glycogen breakdown produces glc that is metabolized via glycolysis to provide ATP for muscle contraction
Glycogen MetabolismGlycogen SynthesisWant to polymerize glc, need an activated form of glc - UDP-glucoseOccurs in almost all tissues, especially in liver and muscle
UDP-glucose pyrophosphorylase
Glycogen synthase
UDP
Glycogenchain
Glycogen chain + one more glucose residue
Glycogen MetabolismGlycogen Synthesis
Glycogen MetabolismGlycogen Synthesis
Glycogen Metabolism
Glycogen SynthesisGlycogen synthase cannot initiate a chain - it needs a primer
Protein enzyme glycogenin makes the primer
Once 8 glucose molecules have been added, Glycogenin-[glc]8 is a substrate for glycogen synthase
Glycogen MetabolismGlycogen SynthesisGlycogen synthase cannot make the (16) bonds found at branches, these are formed by branching enzymes
Glycogen MetabolismGlycogen SynthesisGlycogen synthase cannot make the (16) bonds found at branches, these are formed by branching enzymes
Glycogen MetabolismControlHormones reciprocally regulate synthesis and degradation by controlling the phosphorylation/dephosphorylation of the key enzymes
Glycogen MetabolismControlHormones reciprocally regulate synthesis and degradation by controlling the phosphorylation/dephosphorylation of the key enzymes
Glucagon, epinephrine: stimulate phosphorylaseinhibit synthase
Insulin: inhibit phosphorylasestmulate synthase
(+) Glucagon, epinephrine
(+) Insulin
Glycogen MetabolismControlHormones reciprocally regulate synthesis and degradation by controlling the phosphorylation/dephosphorylation of the key enzymesGlucagon, epinephrine: stimulate phosphorylase & inhibit synthaseInsulin: inhibit phosphorylase & stimulate synthase
Glycogen Metabolism
Glycogen Metabolism
Glycogen Metabolism
Glycogen Metabolism