Biochemistry 2280A Lecture Notes - Lecture 9: Glycogen Phosphorylase, Glycogen Synthase, Glycogen
5 May 2018
School
Department
Course
Professor
Topic 9: Carbohydrate Metabolism
- Glucose-6-Phosphate is the 2nd intermediate of glycolysis
- Fates of Glucose-6-Phosphate:
(1) Glycogen Synthesis
(2) Glycolysis and Fermentation
(3) Gluconeogenesis (Pyruvate Glucose)
(4) Pentose Phosphate Pathway
(1) Glycogen Synthesis
- We store excess sugar/carbs as glycogen
- The liver and muscle cells store most of the glucose
- When glucose goes through glycolysis, the 2nd intermediate, glucose-6-phosphate, is converted to
glucose-1-phosphate...
Glycogen Storage in Muscle and Liver...
Irreversible Reactions –
these two reactions are
the target of regulation
- Glycogen Synthase can take G1P remove its phosphate group
(using UTP hydrolysis) to add glucose to the glycogen polymer
- Glycogen Phosphorylase can add a phosphate group back on to
the glucose in the glycogen polymer to convert it back to G1P
- Glucose-6-Phosphate allosterically regulates the irreversible
reactions. When its concentrations are high, it activates Glycogen
Synthase and inhibits Glycogen Phosphorylase.
- Again, G6P allosterically activates Glycogen Synthase and
allosterically inhibits Glycogen Phosphorylase
- In muscle cells, ATP and AMP are also allosteric regulators.
ATP allosterically inhibits Glycogen Phosphorylase and AMP
allosterically activates Glycogen Phosphorylase.
- Musles are er selfish...the do’t respod to etraellular
signals (like blood glucose, insulin, glucagon) besides
epinephrine, just intracellular signals (like ATP, AMP, and G6P
levels)
find more resources at oneclass.com
find more resources at oneclass.com
- In the liver, Glycogen Synthase and Glycogen Phosphorylase are slightly
different – they are isozymes of the enzymes in skeletal muscles.
- G6P still activates Glycogen Synthase, however, blood glucose inhibits
glycogen phosphorylase
- Liver is very selfless...they respond to extracellular signals (like blood
gluose, isuli, ad gluago ut do’t respod to itraellular sigals
(like ATP, AMP). Livers respond to G6P (intracellular signal) in order to
store it as glycogen when its concentration increases so the brain and the
rest of the body can use this glycogen reservoir.
- Glycogen Synthase and Glycogen Phosphorylase, in both the muscle and
liver, are regulated by phosphorylation.
- When Glycogen Synthase is phosphorylated by protein kinase,
it is inactive and when protein phosphatase takes the phosphate group
off, it is active.
- When Glycogen Phosphorylase is phosphorylated by protein
kinase, it is active and when protein phosphate takes the phosphate
group off, it is inactive.
- The action of kinase and phosphatase (i.e.. when Glycogen Synthase and
Glycogen Phosphorylase are phosphorylated or not) depends on Insulin,
Glucagon, and Epinephrine...
- Insulin is a hormone in the blood – it does not directly
iterat this is’t allosteri iteratio. Whe lood gluose
is high, there is high insulin in the blood, and it binds to a
receptor on the surface of the liver cell which signals a
cascade resulting in dephosphorylation of glycogen synthase
(activates it) and glycogen phosphorylase (inactivates it).
Glycogen can now be formed from the excess glucose.
Liver
- Selfless and sensitive to extracellular signals
(insulin + glucagon)
- Glucagon is a hormone in the blood – it does not directly
iterat this is’t allosteri iteratio. Whe lood
glucose is low, there is high glycogen in the blood and it
binds to a receptor on the surface of the liver cell which
signals cascade resulting in phosphorylation of glycogen
phosphorylase (activates it) and glycogen synthase
(inactivates it) which breaks down glycogen into glucose.
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Glucose-6-phosphate is the 2nd intermediate of glycolysis. Fates of glucose-6-phosphate: (1) glycogen synthesis (2) glycolysis and fermentation (3) gluconeogenesis (pyruvate glucose) (4) pentose phosphate pathway (1) glycogen synthesis. The liver and muscle cells store most of the glucose. When glucose goes through glycolysis, the 2nd intermediate, glucose-6-phosphate, is converted to glucose-1-phosphate Irreversible reactions these two reactions are the target of regulation. Glycogen synthase can take g1p remove its phosphate group (using utp hydrolysis) to add glucose to the glycogen polymer. Glycogen phosphorylase can add a phosphate group back on to the glucose in the glycogen polymer to convert it back to g1p. When its concentrations are high, it activates glycogen. Again, g6p allosterically activates glycogen synthase and allosterically inhibits glycogen phosphorylase. In muscle cells, atp and amp are also allosteric regulators. Atp allosterically inhibits glycogen phosphorylase and amp allosterically activates glycogen phosphorylase.
