Gluconeogenesis Flashcards
Under what state does gluconeogenesis occur?
Fasting state when blood glucose levels are low
Name the 4 precursors of gluconeogenesis
Lactate/pyruvate, Amino acids, Glycerol, Propionyly CoA
What is gluconeogenesis?
The synthesis of new glucose molecules. Gluconeogenesis meets the needs of the body for glucose when sufficient carbohydrate is not available from the diet or glycogen reserves.
How many lactate molecules produces 1 glucose?
2
When lactate converts to glucose, how many ATP molecules are produced?
6
Which key enzyme in lactate to glucose converts pyruvate to OAA and where does it take place?
Pyruvate carboxylase
Takes place in the mitochondrial matrix
Which key enzyme in lactate to glucose converts OAA to phosphoenolpyruvate and where does it take place?
Phosphoenolpyruvate carboxylase (PEPCK)
Takes place in the cytosol
Which key enzyme in lactate to glucose converts Fructose-1,6-bisphophate to Fructose-6-phosphate and where does it take place?
Fructose-1,6-bisphosphatase
Takes place in the cytosol
Which key enzyme in lactate to glucose converts Glucose-6-phosphate to Glucose and where does this take place?
Glucose-6-phosphatase and takes place in the SER
Why is gluconeogenesis not just the reverse of glycolysis?
Because it uses 3 different enzymes in its pathway that are different from the enzymes in glycolysis (at the irreversible steps)
Three nonequilibrium reactions in glycolysis catalyzed by hexokinase,
phosphofructokinase, and pyruvate kinase are considered
thermodynamic barriers which prevent simple reversal of glycolysis
for glucose synthesis.
True or False: Biotin (Vit. B7) is a cofactor needed for gluconeogenesis and what molecule does it require to work properly?
True and ATP and CO2
Which of the following glycolytic enzymes is used in gluconeogenesis?
a) glucokinase
b) phosphofructokinase-1
c) aldolase B
d) Phosphoglycerate kinase
e) pyruvate kinase
D) phosphoglycerate kinase
What is the regulation of Pyruvate Carboxylase?
Beta Oxidation
Hypoglycemia is a defect in _____.
Beta oxidation
What is the allosteric activator of pyruvate carboxlase?
Acetyl CoA
How long can glycogen meet glucose demands before depleting?
<24hrs
What is glucose made from in a fasting state?
Non-carb precursors
Where does gluconeogenesis take place?
Liver and kidneys (and certain places in GIT)
How does propionate enter gluconeogenesis?
Via the citric acid cycle
-major precursor in ruminants
- In non-ruminants, including humans, propionate arises from where?
1) the Beta -oxidation of odd-chain fatty acids that occur in ruminant lipids,
2) the oxidation of isoleucine and the side-chain of cholesterol
Explain how glucose is produced from glycerol and which organs does in occur in?
The triglyceride is broken down into glycerol and fatty acid by lipolysis. The glycerol is then converted to glycerol-3-phosphate which is then converted to dihydroxyacetone phosphate. DHAP can then be converted into Fructose-1,6-bisphosphate which is converted to Fructose-6-phosphate by the enzyme fructose-1,6-bisphosphatase and F-6-P gets converted to Glucose-6-P that enters the SER and is converted to Glucose
Solely as a substrate for gluconeogenesis in the liver and kidneys
What are the three bypass reactions in gluconeogenesis?
- First bypass (Formation of Phosphoenolpyruvate from pyruvate)
- Second bypass (Formation of Fructose 6- phosphate from fructose 1,6-bisphosphate)
- Third bypass (Formation of Glucose by hydrolysis of glucose 6-phosphate)
Is Biotin required for the conversion of pyruvate to OAA?
Yes
Where does the GTP used in the conversion of OAA to PEP come from?
In liver and kidney, the reaction of succinate thiokinase in the citric acid cycle
produces GTP (rather than ATP as in other tissues), and this GTP is used for
the reaction of phosphoenolpyruvate carboxykinase.
