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Chapter 21

BCM 475 Chapter Notes - Chapter 21: Glycogen Phosphorylase, Glycogen Synthase, Glycogenesis


Department
Biochemistry
Course Code
BCM 475
Professor
Welch
Chapter
21

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GLYCOGEN
SYNTHESIS: glucose 1-phosphate + Glycogenn + UTP + H2O glycogenn+1 + UDP + 2Pi
DEGRADATION: Glycogenn+1 + P Glycogenn + glucose-1-phosphate
BENEFITS of GLYCOGEN AS STORAGE MOLECULE (97% efficiency)
- Buffer for maintaining blood-glucose levels
o Glucose is only fuel used by brain (except starvation)
- Glycogen glucose; good for sudden/strenuous activity
- Unlike fatty acids, released glucose can provide energy in absence of oxygen (anaerobically)
- Highly branched many nonreducing ends per molecule
o Many phosphorylases can release many glucose/glycogen
GLYCOGENESIS | GLYCOGEN SYNTHESIS
1. Reversible | Glucose 1-phosphate + UTP UDP-glucose + PPi
2. Irreversible | PPi + H2O 2Pi
---------------------------------------------------------------------------------------------------------------------------------
Irreversible | Glucose 1-phosphate + UTP + H2O UDP-glucose + 2Pi
STEPS
. FORMATION OF GLUCOSE 1-PHOSPHATE
Glucose 6-phosphate glucose 1-phosphate
(*glucose 6-phosphate is incorporated into glycogen
synthesis by the hydrolyzing of 1 ATP)
- Catalyzed by phosphoglucomutase (dual
roles in synthesis/metabolism)
. ENERGY MOLECULE FORMS UDP-GLUCOSE =
PRECURSOR
Glucose 1-phosphate + UTP UDP-glucose + PPi
- UTP forms precursor UDP-glucose
- Catalyzed by UDP-glucose
pyrophosphorylase
. HYDROLYSIS OF PYROPHOSPHATE
- The rapid hydrolysis (irreversible) reaction of pyrophosphate drives the whole reaction
forward (despite reversible 1st step)
UDP-GLUCOSE
Activated form of glucose
- Glucose donor in glycogen biosynthesis
- Activated C-1 with OH group esterified to
diphosphate of UDP
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