Glycogen metabolism

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Glycogen metabolism
Glycogen storage granules in liver contain
glycogen aggregates and enzymes to
degrade/synthesize
-in muscle, rapid energy source for aerobic or
anaerobic metabolism -stored in liver for
dispersal via glucose through bloodstream -possibl
e to metabolize anaerobically -small energy
storage compared to fats, but fats can only
undergo aerobic catabolism
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GP cannot handle branches need
debranching enzyme with two activities
Generates glucose-1-phosphate
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Phosphoglucomutase mechanism two phosphate
transfers
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In liver, glucose-6-phosphate needs to be
converted to glucose for transport to
tissues Glucose 6 phosphatase faces the ER
lumen separate from glycolytic pathway
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Metabolism of galactose involves sugar nucleotides

• C1 carbon activated through
• phosphate ester
• UMP is a good leaving group to
• generate glucose-1-phosphate

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Formation of sugar nucleotides condense
sugar-phosphate with NDP irreversible due to
linked pyrophosphorolysis Allows tagging and
metabolic segregation Glycogen synthesis starts
with UTP reaction with glucose-1-phosphate to
generate UDP glucose (UDP-glucose
pyrophosphorylase)
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Glycogen synthase reaction is the central step in
glycogen synthesis Needs nonreducing end cannot
synthesize branchpoints
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Introduction of branchpoints make glycogen more
soluble increase the number of nonreducing
ends Further addition of glucose may occur to new
non-reducing end Transfers 6-7 monomers from a
chain at least 11 monomers long
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C1
Essential Mn2 ion stabilizes UDP
C4
C1
Synthesis of new glycogen chains requires
glycogenin enzyme Glycogenin initiates and
extends first chain then glycogen synthase
and branching enzyme continue glycogenin remains
in center of particle