Podcast
Questions and Answers
Which of the following is NOT a source for gluconeogenesis?
Which of the following is NOT a source for gluconeogenesis?
What percentage of gluconeogenesis occurs in the liver?
What percentage of gluconeogenesis occurs in the liver?
Why is gluconeogenesis important during prolonged fasting?
Why is gluconeogenesis important during prolonged fasting?
Which enzyme is responsible for the conversion of pyruvate to oxaloacetate?
Which enzyme is responsible for the conversion of pyruvate to oxaloacetate?
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Which of the following hormones is likely to stimulate gluconeogenesis?
Which of the following hormones is likely to stimulate gluconeogenesis?
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Which process does NOT describe gluconeogenesis?
Which process does NOT describe gluconeogenesis?
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What role does malate dehydrogenase play in gluconeogenesis?
What role does malate dehydrogenase play in gluconeogenesis?
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Which enzyme in gluconeogenesis counteracts hexokinase in glycolysis?
Which enzyme in gluconeogenesis counteracts hexokinase in glycolysis?
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Which enzyme is responsible for the conversion of fructose 1,6 biphosphate to fructose-6-phosphate?
Which enzyme is responsible for the conversion of fructose 1,6 biphosphate to fructose-6-phosphate?
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What is the main energy substrate consumed for converting 2 molecules of pyruvate to glucose?
What is the main energy substrate consumed for converting 2 molecules of pyruvate to glucose?
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Which of the following is NOT a gluconeogenic substance?
Which of the following is NOT a gluconeogenic substance?
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What effect does insulin have on gluconeogenesis?
What effect does insulin have on gluconeogenesis?
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Which enzyme is activated by glucagon and epinephrine to stimulate gluconeogenesis?
Which enzyme is activated by glucagon and epinephrine to stimulate gluconeogenesis?
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Which pathway is inhibited when gluconeogenesis is active?
Which pathway is inhibited when gluconeogenesis is active?
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Which compound is derived from lipids during fasting and is involved in gluconeogenesis?
Which compound is derived from lipids during fasting and is involved in gluconeogenesis?
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What stimulates gluconeogenesis by inducing the synthesis of key enzymes?
What stimulates gluconeogenesis by inducing the synthesis of key enzymes?
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Study Notes
Gluconeogenesis Definition
- Gluconeogenesis is the synthesis of glucose or glycogen from non-carbohydrate sources
- These sources include lactic acid, pyruvic acid, propionic acid, glycerol, and amino acids
Gluconeogenesis Site
- The primary site is the liver (90%) and the kidney (10%)
- Gluconeogenesis occurs in both the cytoplasm and mitochondria
Gluconeogenesis Importance
- Provides blood glucose during fasting periods (more than 18 hours) when glycogen stores are depleted
- Is the sole energy source for nervous tissue, red blood cells (RBCs), and skeletal muscle during exercise.
- Is a precursor for milk sugar (lactose) in mammary glands
- Clears waste products from the blood, such as lactic acid produced in skeletal muscles and RBCs
Gluconeogenesis Steps
- Gluconeogenesis is mainly the reversal of glycolysis, except for three irreversible kinases
- These irreversible steps are overcome by specific enzymes
- Enzymes of glycolysis include: Pyruvate kinase, Phosphofructokinase-1, Hexokinase & glucokinase
- Enzymes of gluconeogenesis include:
- Pyruvate carboxylase (mitochondrial), Phosphoenol pyruvate carboxykinase
- Fructose 1,6 biphosphatase
- Glucose-6-phosphatase
Gluconeogenesis Substrates
- Gluconeogenic amino acids - critical nitrogen and carbon sources
- Pyruvate and Lactate
- Propionate
- Propionic acid is converted to succinyl CoA only in ruminants
- Glycerol
- Derived from lipids in adipose tissue during fasting
- Converted to glycerol-3-phosphate, then dihydroxyacetone phosphate
Energy Cost
- Converting 2 pyruvate molecules to glucose consumes 6 ATP molecules and 2 NADH+ H+
Gluconeogenesis Regulation
- Gluconeogenesis and glycolysis are coordinated pathways. If one is active, the other should be inhibited
- Key regulatory enzymes include:
- Pyruvate carboxylase
- Phosphoenol pyruvate carboxykinase
- Fructose 1,6-biphosphatase
- Glucose-6-phosphatase
- Regulation occurs through:
- Changes in enzyme synthesis
- Glucocorticoids (e.g., cortisol) stimulate gluconeogenesis by inducing enzyme synthesis, and increase protein catabolism to provide gluconeogenic amino acids.
- Insulin inhibits gluconeogenesis by reducing enzyme synthesis
- Covalent modification
- Glucagon and epinephrine stimulate gluconeogenesis by phosphorylating pyruvate kinase, inhibiting glycolysis, and stimulating gluconeogenesis.
- Allosteric regulation
- Acetyl-CoA is an allosteric activator of pyruvate carboxylase. Derived from fat oxidation, high levels indicate increased gluconeogenesis.
- Fructose-2,6-bisphosphate (a glycolysis regulator) is relevant in gluconeogenesis regulation
- Changes in enzyme synthesis
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Description
Explore the essential process of gluconeogenesis, where glucose is synthesized from non-carbohydrate sources like lactic acid and glycerol. This quiz covers the importance, sites, and steps of gluconeogenesis, highlighting its critical role during fasting and exercise. Test your knowledge and deepen your understanding of this vital metabolic pathway.
