Chapter 10
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Questions and Answers

Which reaction is catalyzed by a biotin-requiring enzyme?

  • Acetyl CoA → Fatty acids
  • Pyruvate → Lactate
  • Oxaloacetate → Phosphoenolpyruvate
  • Pyruvate → Oxaloacetate (correct)
  • Which of the following reactions is specific to gluconeogenesis?

  • Lactate → Pyruvate
  • Oxaloacetate → Phosphoenolpyruvate (correct)
  • Phosphoenolpyruvate → Pyruvate
  • 1,3-Bisphosphoglycerate → 3-Phosphoglycerate
  • What is the effect of adenosine monophosphate (AMP) on gluconeogenesis?

  • No effect on gluconeogenesis
  • Inhibits glycolysis
  • Activates gluconeogenesis
  • Inhibits gluconeogenesis (correct)
  • What happens to the NAD+/NADH ratio during the metabolism of ethanol?

    <p>Increases NADH significantly</p> Signup and view all the answers

    Which substrate's availability is decreased due to the increase of NADH during ethanol metabolism?

    <p>Oxaloacetate</p> Signup and view all the answers

    How does acetyl CoA influence gluconeogenesis?

    <p>Activates pyruvate carboxylase and inhibits pyruvate dehydrogenase</p> Signup and view all the answers

    Which enzyme is downregulated by both fructose 2,6-bisphosphate and adenosine monophosphate?

    <p>Fructose 1,6-bisphosphatase</p> Signup and view all the answers

    Which coenzyme is required by the pyruvate dehydrogenase complex?

    <p>Thiamine pyrophosphate</p> Signup and view all the answers

    What is the primary consequence of decreased availability of oxaloacetate on gluconeogenesis?

    <p>Decreased gluconeogenesis</p> Signup and view all the answers

    Which role does lactate play in gluconeogenesis?

    <p>It is converted to pyruvate</p> Signup and view all the answers

    Which precursor is NOT involved in gluconeogenesis?

    <p>Glucose from dietary intake</p> Signup and view all the answers

    Which enzyme is NOT one of the three physiologically irreversible reactions in gluconeogenesis?

    <p>Fructose 1,6-bisphosphatase</p> Signup and view all the answers

    Which molecule activates pyruvate carboxylase in gluconeogenesis?

    <p>Acetyl coenzyme A</p> Signup and view all the answers

    What effect does a rise in AMP have on gluconeogenesis?

    <p>Inhibits fructose 1,6-bisphosphatase</p> Signup and view all the answers

    Which hormone is NOT associated with stimulating gluconeogenesis?

    <p>Insulin</p> Signup and view all the answers

    Which substrate is primarily utilized in gluconeogenesis during prolonged fasting?

    <p>Lactate</p> Signup and view all the answers

    Where does the final step of gluconeogenesis occur?

    <p>Endoplasmic reticulum</p> Signup and view all the answers

    Which reaction is performed by PEP carboxykinase in gluconeogenesis?

    <p>Conversion of pyruvate to phosphoenolpyruvate</p> Signup and view all the answers

    What is the effect of fatty acid degradation on gluconeogenesis?

    <p>It generates acetyl coenzyme A, which cannot be converted to glucose</p> Signup and view all the answers

    Which enzyme's deficiency results in severe fasting hypoglycemia?

    <p>Glucose 6-phosphatase</p> Signup and view all the answers

    Study Notes

    Gluconeogenesis Overview

    • Gluconeogenesis uses precursors such as glycolytic and TCA cycle intermediates, glycerol, lactate, and α-keto acids from glucogenic amino acids.
    • It is essential for maintaining blood glucose levels during fasting, especially as glycogen stores deplete.

    Key Enzymatic Reactions

    • Seven glycolysis reactions are reversible and are also utilized in gluconeogenesis.
    • Three irreversible reactions require alternative pathways:
      • Pyruvate kinase
      • Phosphofructokinase
      • Hexokinase

    Reversible Steps

    • Pyruvate is converted to oxaloacetate by pyruvate carboxylase, which requires:
      • Biotin
      • ATP
      • Allosteric activation by acetyl CoA
    • Oxaloacetate is then converted to phosphoenolpyruvate (PEP) by PEP carboxykinase, which requires GTP.
    • Fructose 1,6-bisphosphate is converted to fructose 6-phosphate via fructose 1,6-bisphosphatase, regulated by:
      • Inhibition by AMP
      • Activation by ATP
      • Inhibition by fructose 2,6-bisphosphate (a glycolysis activator)
    • Glucose is formed from glucose 6-phosphate by glucose 6-phosphatase, crucial in gluconeogenesis and glycogen degradation.

    Hormonal Regulation

    • Gluconeogenesis is stimulated by low insulin/high glucagon ratios.
    • Glucagon and glucocorticoids increase transcription of the gene for PEP carboxykinase while insulin decreases it.

    Fatty Acid and Amino Acid Metabolism

    • Fatty acid degradation produces acetyl CoA, which cannot lead to glucose formation; it influences gluconeogenesis indirectly.
    • Gluconeogenic substrates mainly derive from amino acid carbon skeletons, not from acetyl CoA.

    Inhibition Factors

    • Large amounts of avidin inhibit pyruvate carboxylase by sequestering biotin.
    • The increase in NADH from ethanol metabolism reduces oxaloacetate production, thereby decreasing gluconeogenesis.

    Key Inhibitory and Regulatory Molecules

    • AMP and fructose 2,6-bisphosphate downregulate gluconeogenesis via inhibition of fructose 1,6-bisphosphatase and promote glycolysis through activation of phosphofructokinase-1.

    Acetyl CoA Role

    • Acetyl CoA inhibits pyruvate dehydrogenase, redirecting pyruvate from oxidation towards gluconeogenesis via activation of pyruvate carboxylase.

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    Description

    This quiz explores the gluconeogenic precursors derived from glycolysis and the tricarboxylic acid cycle. You will learn about the various substrates involved, including lactate, glycerol, and α-keto acids, as well as the key reversible reactions utilized in gluconeogenesis. Test your knowledge on the complex interplay of these metabolic pathways.

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