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Title: GLUCONEOGENESIS EXPLAINED
Description: Simple to understand notes notes on carbohydrate metabolism for anyone pursuing a Bachelor's Degree in Biochemistry or Biology. I use these notes to lecture Biochemistry at the University of Zambia.
Description: Simple to understand notes notes on carbohydrate metabolism for anyone pursuing a Bachelor's Degree in Biochemistry or Biology. I use these notes to lecture Biochemistry at the University of Zambia.
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Gluconeogenesis
C LULEMBO
1
• Definition: The synthesis of glucose from non carbohydrate
precursors
• Major substrates are: glucogenic amino acids, lactate, glycerol, and
propionate
• Liver and kidney are the major gluconeogenic tissues
• Meets needs of the body for glucose when carbohydrates is not
available in sufficient amount from the diet or glycogen reserves
• A supply of glucose is necessary because the brain and
erythrocytes are highly dependent on glucose as the primary fuel
• A typical adult brain requires about 120g glucose per day, which
accounts for most of the 160g of glucose needed by the whole body
• Gluconeogenesis also -maintains levels of citric acid cycle
intermediates
•
-clears lactate produced by skeletal
muscles and red blood cells
-clears glycerol produced by adipose tissue
2
Thermodynamic barriers prevent reversal of glycolysis
-Three nonequilibrium reactions catalysed by hexokinase,
phosphofructokinase and pyruvate kinase prevent reversal of glycolysis
for gluconeogenesis
These are bypassed by the following new steps:
i)
Pyruvate and phosphoenolpyruvate
Mitochondrial pyruvate carboxylase catalyze the carboxylation of
pyruvate to oxaloacetate
...
The enzyme is present in liver, kidney and skeletal muscles
iii)
Glucose 6-phosphate and glucose
Catalyzed by glucose 6-phosphatase
The enzyme is present in liver and kidney
Glucose 6-phosphatase is not present in brain and muscle;
hence glucose cannot be formed by these organs
...
It is
converted to dihydroxyacetone phosphate which is converted to glucose
via gluconeogenesis
8
Hormone control
• Insulin which rises following feeding stimulates formation of
phosphofructokinase-1, pyruvate kinase
• Glucagon which rises during starvation, inhibits the expression of these
enzymes and instead promotes expression of key gluconeogenic enzymes
phosphoenolpyruvate carboxykinase and fructose 1,6bisphosphatase
...
• In the liver lactate is oxidized to pyruvate ,
• The liver furnishes glucose to contracting skeletal muscle, which derives
ATP from the glycolytic conversion of glucose to lactate
...
These reactions constitute the Cori
cycle
9
The Cori cycle
Liver
Glucose
Muscle
Glucose
Glycolysis
Gluconeogenesis
Pyruvate
Pyruvate
Lactate
Lactate
10
1
...
3
...
5
Title: GLUCONEOGENESIS EXPLAINED
Description: Simple to understand notes notes on carbohydrate metabolism for anyone pursuing a Bachelor's Degree in Biochemistry or Biology. I use these notes to lecture Biochemistry at the University of Zambia.
Description: Simple to understand notes notes on carbohydrate metabolism for anyone pursuing a Bachelor's Degree in Biochemistry or Biology. I use these notes to lecture Biochemistry at the University of Zambia.