Gluconeogenesis Flashcards
What will be used to supply the bodies glucose when fasting for less than 24 hours?
Liver glycogen
What supplies the body with glucose overnight?
Glycogenolysis and gluconeogenesis about equally
What are the major tissues for gluconeogenesis?
Liver and kidney
When does the kidneys contribution to gluconeogenesis become more important?
With starvation
What are the noncarbohydrate for gluconeogenesis?
Glycerol
Glucogenic AA
Lactate
Propionate - minor in humans
What are the three reactions that prevent gluconeogenesis from being a reversal of glycolysis?
Hexokinase
PFK-1
Pyruvate kinase
How does gluconeogenesis bypass pyruvate kinase?
Changes pyruvate into oxaloacetate by pyruvate carboxylase
Changes oxaloacetate to phosphoenolpyruvate by PEP carboxylase
What is required to change pyruvate to oxaloacetate?
ATP to ADP with Mg
Biotin
Mn
CO2
H2O
Where does the reaction of pyruvate to oxaloacetate take place?
Mitochondria
How is oxaloacetate transported from the mitochondria to the cytosol?
It is reduced to malate and reoxidized in the cytosol using NAD
What is required to change oxaloacetate into phosphoenolpyruvate?
GTP to GDP
Produces CO2
How does gluconeogenesis bypass PFK-1?
Fructose-1,6P to fructose 6P by fructose-1,6-bisphosphatase
Using H2O and resulting in a Pi
How does gluconeogenesis bypass hexokinase?
Glucose-6P to glucose by glucose-6-phosphatase with H2O
Where does the reaction catalyzed by glucose 6 phosphate take place?
Membrane of ER
How many pyruvates are needed to make 1 glucose?
Two
What is the energy investment needed for gluconeogenesis?
4 ATP
2 GTP
How does glucagon affect gluconeogenesis through induction/repression?
Stimulates production of phosphoenolpyruvate carboxykinase and F1,6-bisphosphotase, thereby increasing gluconeogenesis
It also represses the transcription of enzymes used in glycolysis
How do glucagon and epinephrine increase gluconeogenesis through phosphorylation?
Bind to g-protein, increasing concentration of cAMP. This activate cAMP dependent protein kinase which will phosphorylate PK and inactivate it.
How does acetyl CoA affect gluconeogenesis?
It is an activator of pyruvate carboxylase and inhibits PDH
What is an inhibitor of pyruvate carboxylase?
ADP
What activates F1,6-bisphosphatase?
Citrate
What inhibits F1,6-bisphosphatase?
AMP
F2,6 bisphosphate
What AAs are not glucogenic?
Leucine
Lysine
What is the Cori cycle?
Lactate produced in muscle is transported to liver and turned back into glucose. The glucose is released from the liver and returned to the muscles.
Where does glycerol enter the pathway for either gluconeogenesis or glycolysis?
DHAP - dihydroxyacetone phosphate
How is DHAP made from glycerol?
In liver and kidneys. Glycerol to glycerol phosphate by glycerol kinase using ATP.
Glycerol phosphate to DHAP by glycerol phosphate DH using NAD
What is required as a coenzyme to change propionate to succinyl CoA?
Vitamin B12
How can raw egg whites affect gluconeogenesis?
They contain avidin which binds biotin preventing its absorption in the intestine. Biotin is needed for pyruvate carboxylase activity.
How can alcohol inhibit gluconeogenesis?
Results in excessive NADH inhibiting FA oxidation.
Favors pyruvate to lactate to make NAD, instead of gluconeogenesis pathway.
Why can there be hypoglycemia in premature and LBW infants?
Little adipose tissue for FA oxidation
Immature gluconeogenesis enzymes
Inadequate stores of glycogen
Why may there be hypoglycemia in an infant with a diabetic mother?
Hyperglycemia from mother leads to hyperplasia of pancreatic islet cells that produce more insulin - baby fails to suppress excessive insulin production after birth
