Questions and Answers
What is required for the reversal of the glyceraldehyde-3-phosphate dehydrogenase reaction?
When pyruvate is the gluconeogenic substrate, which reaction supplies NADH?
What is the product of the condensation of 1 mole of DHAP and 1 mole of glyceraldehyde-3-phosphate?
What is the function of glucose-6-phosphatase in hepatocytes?
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Which three reactions of glycolysis are bypassed during gluconeogenesis?
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What is the fate of glucose-6-phosphate produced in non-hepatic tissues?
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What is the function of gluconeogenesis in skeletal muscle?
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What is the product of the reaction catalyzed by the enzyme pyruvate carboxylase?
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What is the primary function of gluconeogenesis?
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Which of the following is NOT a substrate for gluconeogenesis?
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What is the primary site of gluconeogenesis in the body?
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Which of the following enzymes is NOT involved in gluconeogenesis?
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Why is gluconeogenesis considered energetically expensive?
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Which organ relies primarily on glucose as its energy source?
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What is the alternative energy source for the brain during starvation?
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What is the relationship between gluconeogenesis and glycolysis?
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Study Notes
Gluconeogenesis Overview
- Gluconeogenesis is a metabolic pathway that generates glucose from non-carbohydrate carbon substrates such as lactate, glycerol, and glucogenic amino acids.
- It is one of the two main mechanisms the body uses to maintain blood glucose levels and prevent hypoglycemia.
- Glucose is the sole energy source for the brain, testes, erythrocytes, and kidney medulla.
Importance of Gluconeogenesis
- During starvation, the brain can derive energy from ketone bodies instead of glucose.
- The liver is the major site of gluconeogenesis, with the kidney also playing an important role.
- Gluconeogenesis is necessary for maintaining blood glucose levels, particularly during fasting or starvation.
Key Enzymes
- Pyruvate carboxylase
- Fructose-1,6-bisphosphatase
- Glucose-6-phosphatase
Energy Cost of Gluconeogenesis
- Gluconeogenesis from 2 moles of pyruvate to 2 moles of 1,3-bisphosphoglycerate consumes 6 moles of ATP.
- This process is very costly from an energy standpoint, as glycolysis to 2 moles of pyruvate only yields 2 moles of ATP.
Gluconeogenic Pathway
- The pathway involves the reversal of glycolysis, with three bypass steps that use different enzymes.
- The three bypassed reactions are those catalyzed by pyruvate kinase, phosphofructokinase-1 (PFK-1), and hexokinase/glucokinase.
- The reactions of gluconeogenesis are essentially a reversal of glycolysis.
Tissue-Specific Gluconeogenesis
- In hepatocytes, glucose-6-phosphatase allows the liver to supply the blood with free glucose.
- In non-hepatic tissues, glucose-6-phosphate is a substrate for glycogen synthesis.
- Skeletal muscle lacks glucose-6-phosphatase and undergoes gluconeogenesis exclusively for glycogen storage.
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Description
Learn about gluconeogenesis, a metabolic pathway that generates glucose from non-carbohydrate carbon substrates, and its role in maintaining blood glucose levels.
