Gluconeogenesis Flashcards
What is gluconeogenesis?
Formation of glucose from non-carbohydrate precursors.
What is the main function of gluconeogenesis?
Maintains blood glucose levels during fasting, starvation, or low carbohydrate intake.
Where does gluconeogenesis primarily occur?
Cytoplasm and mitochondria of the liver and kidney.
In which tissues is gluconeogenesis not present?
Brain and muscle due to the absence of glucose-6-phosphatase.
Why is gluconeogenesis important?
Provides fuel for energy-demanding tissues, such as the brain, erythrocytes, kidney medulla, and exercising muscle.
Which three irreversible steps in glycolysis are bypassed in gluconeogenesis?
Hexokinase/Glucokinase, Phosphofructokinase-1 (PFK-1), Pyruvate Kinase.
What enzyme bypasses hexokinase/glucokinase in gluconeogenesis?
Glucose-6-Phosphatase.
What enzyme bypasses Phosphofructokinase-1 (PFK-1) in gluconeogenesis?
Fructose-1,6-Bisphosphatase.
What enzymes bypass pyruvate kinase in gluconeogenesis?
Pyruvate Carboxylase and PEP Carboxykinase.
What is the first step in gluconeogenesis involving pyruvate?
Conversion of Pyruvate to Phosphoenolpyruvate (PEP).
What enzymes are involved in the conversion of pyruvate to PEP?
Pyruvate Carboxylase (mitochondria) and PEP Carboxykinase (cytosol).
How is oxaloacetate transported from mitochondria to cytosol?
As malate.
What enzyme converts Fructose-1,6-Bisphosphate to Fructose-6-Phosphate?
Fructose-1,6-Bisphosphatase.
What enzyme converts Glucose-6-Phosphate to Glucose?
Glucose-6-Phosphatase.
Which substrate is involved in gluconeogenesis via the Cori Cycle?
Lactate.
What happens to lactate in gluconeogenesis?
Converted into pyruvate in the liver and then into glucose.
What are glucogenic amino acids?
Amino acids that undergo deamination to produce pyruvate or other gluconeogenic intermediates.
What is the primary source of glucose after 18 hours of fasting?
Proteins.
What role does glycerol play in gluconeogenesis?
Derived from lipolysis of triglycerides; converted into dihydroxyacetone phosphate (DHAP).
How is alanine used in gluconeogenesis?
Alanine from skeletal muscles is converted to pyruvate in the liver.
True or False: Acetyl-CoA can be used as a substrate for gluconeogenesis. Explain your answer
False.
Because of the irreversible pyruvate dehydrogenase reaction
What is the physiological importance of gluconeogenesis?
Essential during prolonged fasting, starvation, and intense exercise.
How does gluconeogenesis help with metabolic waste removal?
Converts lactic acid into glucose, reducing acidosis.
Removes glycerol produced during lipolysis
What pathways are connected to gluconeogenesis?
Cori cycle and glucose-alanine cycle support metabolic balance
What can deficiencies in gluconeogenesis enzymes lead to?
Hypoglycemia and metabolic acidosis.
What does Glucose-6-Phosphatase do?
Converts glucose-6-phosphate to glucose.
What does Fructose-1,6-Bisphosphatase do?
Converts fructose-1,6-bisphosphate to fructose-6-phosphate.
What is the significance of gluconeogenesis?
Essential for maintaining glucose levels under carbohydrate-deficient conditions.
Which organs are the primary sites for gluconeogenesis?
Liver and kidney.
What do key bypass enzymes in gluconeogenesis allow?
Overcome irreversible steps of glycolysis.
What substrates fuel gluconeogenesis?
- Lactate
- Glycerol
- Glucogenic amino acids.
How does gluconeogenesis integrate with other metabolic cycles?
Supports metabolic balance through the Cori and glucose-alanine cycles.
Pyruvate carboxylase and PEP carboxykinase convert what
Pyruvate to phosphoenolpyruvate (by passing pyruvate kinase)
