Gluconeogenesis Flashcards
What non-carbohydrate sources can glucose be synthesized from if it is not available from glycogen breakdown or dietary sources?
1) Glycolysis products
2) Lactate
3) Pyruvate
4) TCA cycle intermediates
5) Carbon skeletons of most amino acids
Which two amino acids are broken down to acetyl-CoA instead of oxaloacetate? Can they be the precusors of glucose?
Leucine and Lysine; no
What four-carbon compound are non-carbohydrate sources for glucose broken down to?
oxaloacetate
True or false: Fatty acids can not serve as precursors to glucose. Why?
True; fatty acids are degraded to acetyl-CoA, which cannot be converted to oxaloacetate.
True or false: Acetyl Co-A can be converted to oxaloacetate and used to synthesyze glucose.
False; no pathway exists to convert acetyl-CoA to glucose.
What is the product of gluconeogenesis?
glucose
Which reactions in glycolysis are not reversible?
1) Hexakinase
2) Phosphofructokinase
3) Pyruvate kinase
What enzyme catalyzes the conversion of pyruvate and HCO3- to oxaloacetate?
Pyruvate carboxylase
What reaction does pyruvate carboxylase catalyze?
Pyruvate and HCO3- to oxaloacetate
Is the reaction from pyruvate to oxaloacetate endergonic or exergonic?
Endergonic
What drives the reaction of pyruvate to oxaloacetate that is catalyzed by pyruvate carboxylase?
ATP hydrolysis
True or false: Oxaloacetate is a “high energy” compound?
True
What provides the energy needed to synthesized PEP (via PEP carboxykinase-PEPCK)?
The exergonic decarboxilation of oxaloacetate
Which enzyme catalyzes the reaction of oxaloacetate to PEP?
PEP carboxykinase (PEPCK)
Where does the phosphoryl group that is added to oxaloacetate to make it PEP come from?
From GTP
What two enzymes do the reverse reaction of pyruvate kinase (i.e., take pyruvate to phosphoenolpyruvate)?
1) Pyruvate carboxylase
2) PEP carboxykinase (PEPCK)
For which two pathways does oxaloacetate serve as an intermediate?
Gluconeogenesis and the TCA cycle
Why is maintaining glucose levels in the body important?
Glucose is the only source of fuel for red blood cells and the primary source of fuel for the brain.
How long can glycogen stores in the body supply the body with glucose during a fast?
About one day
What is the major site of gluconeogenesis?
Liver (some also takes place in the kidneys)
True or false: The liver, kidneys, brain, heart, and skeletal muscle are all key sites of gluconeogenesis.
False. Only the liver and kidneys.
Where do the brain and muscle get glucose from when the body is in a fasting state?
From the blood (into which the liver and kidneys deposit the glucose derived from gluconeogenesis).
What substrate does gluconeogenesis convert into glucose?
pyruvate
What are the major non-carbohydrate precursors of glucose?
lactate, amino acids, and glycerol
What enzyme in the liver converts lactate into pyruvate?
lactate dehydrogenase
True or false: Animals can convert fatty acids into glucose.
False
How can glycerols be converted into glucose?
They can be metabolized by glycolysis and then converted to glucose through gluconeogenesis.
What molecule can glycerol be converted to that allows it to enter either the glycolytic or gluconeogenic pathway?
Dihydroxyacteone phosphate
How does gluconeogenesis bypass the three irreversible steps of glycolysis?
1) PEP is formed from pyruvate by way of oxaloacetate.
2) F6P is formed from F-1,6-BP by hydrolysis.
3) Glucose is formed from G6P by hydrolysis.
