Gluconeogenesis Flashcards
What does gluconeogenesis do?
Coverts non-carbohydrate substrates (pyruvate) into glucose
What can the non-carbohydrate substances be?
pyruvate, lactate, glycogenic amino acids, TCA cycle intermediates, odd-chain fatty acids
In mammals when does gluconeogenesis work?
fasting or starving state
Where does gluconeogenesis operate?
in liver and sometimes kidney
Is gluconeogenesis the simple reversal of glycolysis?
no because glycolysis has 7 reversible reactions but 3 non-reversible reactions and converts phosphoenolpyruvate to pyruvate directly whereas gluconeogenesis converts pyruvate to oxaloacetate and oxaloacetate to phosphoenolpyruvate
What is the cori cycle?
The cycle where pyruvate is converted into glucose in the liver and is then transported in the blood to a muscle where it is converted into pyruvate. The pyruvate is then converted into lactate which is transported in the blood to the liver where it is converted to pyruvate
How is pyruvate synthesised from lactate?
using the enzyme lactate dehydrogenase and converting NAD+ to NADH
How is glycerol prepared to be used as a precursor in gluconeogenesis?
Hydrolysis of triglycerides by lipase in adipose tissue to produce glycerol and fatty acids
How does glycerol become involved in gluconeogenesis?
its converted into dihydroxyacetone phosphate and introduced into gluconeogenesis. (using. glycerol kinase to convert it into glycerol-3-phosphate and then glycerol phosphate dehydrogenase to convert it into DHAP)
What can’t be used as a precursor for gluconeogenesis?
Fatty acids
What happens to fatty acids instead of being used for gluconeogenesis?
beta oxidation produces acetyl-CoA which enters into the TCA cycle to be decarboxylated.
FAs are the last source to enter into the TCA cycle
What happens when you use glycogenic amino acids as a precursor?
- Catabolism of these amino acids yields pyruvate or one of the intermediates of the TCA cycle
- These intermediates acts as a substrate for gluconeogenesis
What are the metabolic reactions different to gluconeogenesis?
Pyruvate to oxaloacetate
Oxaloacetate to phosphoenolpyruvate
Fructose-1,6-bisphosphate to fructose-6-phosphate
Glucose-6-phosphate to glucose
What is the reaction converting pyruvate to oxaloacetate?
pyruvic acid + CO2 + H2O =oxaloacetic + Pi
using pyruvate carboxylase and ATP
How does the reaction converting pyruvate to oxaloacetate work?
-3 stage process involving CO2 activation, followed by binding to a biotin binding site on enzyme followed by carboxylation of pyruvate
Where does the reaction converting pyruvate to oxaloacetate occur?
Mitochondria
How is oxaloacetate exported out of the mitochondria to the cytosol?
- in the mitochondria oxaloacetate is reduced to malate (with production of NAD+)
- malate is transported to the cytosol where it is oxidised to oxaloacetate to produce NADH
How is oxaloacetic acid converted to phosphoenolpyruvate?
-It uses one GTP (donates P)
-PEP carboxykinase as the enzyme
and produces CO2
How do you convert fructose-1,6-biphosphate to fructose-6-phosphate?
- hydrolysis reaction of a phosphoric acid monoester (lose phosphate from 1 position)
- uses fructose-1,6-biphosphatase
What is the net reaction of gluconeogenesis?
2 pyruvate + 4ATP + 2GTP + 2NADH + 6H2O
glucose + 4ADP + 2GDP + 6Pi + 2NAD+ + 2H+