BMS2021 Lecture Notes - Lecture 4: Allopurinol, Malic Acid, Methotrexate
30 May 2018
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Week 2. Glucose homeostasis and nitrogen
metabolism
MAINTENANCE OF GLUCOSE HOMEOSTASIS II
• Achieved by regulating glycogen metabolism
o Liver: glycogen synthesis takes place in the fed state while glycogenolysis accelerates
during fasting
o Muscle: glycogenolysis occurs during exercise and glycogen synthesis begins when at
rest
• Achieved at two levels:
o (1) Allosteric regulation of glycogen synthase and glycogen phosphorylase
o (2) Pathways of synthesis and breakdown are hormonally regulated
• Glycogen granules may not be seen after sleep/fasting and during exercise in muscles
(~55,000 glucose units attached)
• Glycogenolysis:
o Glucose residues are removed from glycogen by Glycogen Phosphorylase
-GP removed Glucose-1-phosphate (G-1-P)
-a’t at at ahig points, comes back when branch is hydrolysed
-when glucose levels return to normal, glucose enters liver cell and binds to allosteric
site on phosphorylase to inhibit the enzyme -> less glycogen breakdown
o G-6-P is dephosphorylated in the liver for transport out
-Glucose-6-phosphatase is seuesteed i edoplasi etiulu esues live does’t
use up glucose for its own needs)
o Control of glycogen breakdown: Glucagon/epinephrine signalling pathway
-starts phosphorylation cascade via cAMP -> causes phosphorylation of phosphorylase ->
breakdown of glycogen
find more resources at oneclass.com
find more resources at oneclass.com
• Glycogen synthesis:
o Glycogen is synthesised by Glycogen synthase (energy storage)
o Controlled by phosphorylation
o Also controlled by insulin-signalling pathway
-increases glucose import into muscle -> stimulates muscle hexokinase ->enables
activation of glucose
-activates glycogen synthase (phosphorylated = inactive)
find more resources at oneclass.com
find more resources at oneclass.com
• Regulation of glycogen synthesis and breakdown:
o Kinase and phosphatase are reversible
-can inhibit or activate
o Kinase phosphorylates = inactivated
o Phosphatase dephosphorylates = active
o Phosphorylase activated = breakdown
• Coordination and control of carbohydrate metabolism
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
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