8/10/2019 Lec 20 Glycogen 2014
1/20
Glycogen Metabolism
Reducing end
**Small amounts of glycogen in red blood cells & kidneyVERY small amounts of glycogen in certain glial cells and white blood cells
**
8/10/2019 Lec 20 Glycogen 2014
2/20
Glycogen MetabolismGlycogen Breakdown (Glycogenolysis) and Glycogen Synthesis
Why breakdown glycogen and not lipid to produce glc?
1. Mobilized faster
2. Can be metabolized anaerobically
lycogen breakdownlc units are removed one at a time from the nonreducing ends by
hosphorolysis
8/10/2019 Lec 20 Glycogen 2014
3/20
Glycogen MetabolismGlycogen Breakdown
Remove all the 14 branches and an additional enzyme is recd to
remove 16
8/10/2019 Lec 20 Glycogen 2014
4/20
Glycogen MetabolismGlycogen Breakdown - Glycogen phosphorylase
First known example of an allosterically regulated enzyme
First enzyme shown to be controlled by reversible phosphorylation
In muscle:
Resting muscle
During vigorous muscular
activity, epinephrine
triggers phos
Triggers glycogen
breakdown
8/10/2019 Lec 20 Glycogen 2014
5/20
8/10/2019 Lec 20 Glycogen 2014
6/20
Glycogen MetabolismGlycogen Breakdown - Glycogen phosphorylase
In liver:
Low blood sugar -
glucagon activates
phosphorylase b kinase,initiates release of glc
into blood
phosphorylase kinase
8/10/2019 Lec 20 Glycogen 2014
7/20
Glycogen MetabolismGlycogen Breakdown
Fate of glucose 1-phosphate
Muscle / liver
phosphoglucomutase
G1P G6P Glycolysis
If you just need glucose:
Liver
Gluconeogenesis or
glucose 6-phosphatase
Glycogen
G1P
G6P + H2O
Glc + Pi
In brain & muscle:
No gluconeogenesis and no glucose 6-phosphatase so
get 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
8/10/2019 Lec 20 Glycogen 2014
8/20
Glycogen MetabolismGlycogen Synthesis
Want to polymerize glc, need an activated form of glc - UDP-glucose
Occurs in almost all tissues, especially in liver and muscle
UDP-glucose
pyrophosphorylase
Glycogen synthase
UDP
Glycogen
chain
Glycogen chain + one more glucose residue
8/10/2019 Lec 20 Glycogen 2014
9/20
8/10/2019 Lec 20 Glycogen 2014
10/20
Glycogen Metabolism
lycogen Synthesis
8/10/2019 Lec 20 Glycogen 2014
11/20
Glycogen Metabolism
lycogen Synthesis
lycogen synthase cannot initiate ahain - it needs a primer
rotein enzyme glycogeninmakes the
rimer
nce 8 glucose molecules have been
dded, Glycogenin-[glc]8 is a
ubstrate for glycogen synthase
8/10/2019 Lec 20 Glycogen 2014
12/20
8/10/2019 Lec 20 Glycogen 2014
13/20
8/10/2019 Lec 20 Glycogen 2014
14/20
Glycogen Metabolism
ontrol
ormones reciprocally regulate synthesis and degradation by controllin
e phosphorylation/dephosphorylation of the key enzymes
lucagon, epinephrine: stimulate phosphorylase & inhibit synthase
nsulin:inhibit phosphorylase & stimulate synthase
8/10/2019 Lec 20 Glycogen 2014
15/20
8/10/2019 Lec 20 Glycogen 2014
16/20
Glycogen Metabolism
ontrol
ormones reciprocally regulate synthesis and degradation by controllin
e phosphorylation/dephosphorylation of the key enzymes
lucagon, epinephrine: stimulate phosphorylaseinhibit synthase
nsulin: inhibit phosphorylase
stmulate synthase
(+)
Glucagon,
epinephrine
(+)
Insulin
8/10/2019 Lec 20 Glycogen 2014
17/20
Glycogen Metabolism
8/10/2019 Lec 20 Glycogen 2014
18/20
Glycogen Metabolism
Low blood sugar
8/10/2019 Lec 20 Glycogen 2014
19/20
Glycogen Metabolism
8/10/2019 Lec 20 Glycogen 2014
20/20
Glycogen Metabolism
Top Related