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Overview of Gluconeogenesis
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Overview of Gluconeogenesis

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Questions and Answers

Which of the following conditions is associated with gluconeogenesis?

  • Cori's Disease
  • Von Gierke’s Disease (correct)
  • Phenylketonuria
  • Maple Syrup Urine Disease

    • What is one of the functions of gluconeogenesis?

  • Maintains adequate blood sugar during starvation (correct)
  • Generates glucose from fatty acid
  • Synthesis of steroids
  • Supports anaerobic respiration

    • Which tissues require a continuous supply of glucose?

  • Brain and lens of the eye (correct)
  • Cartilage and Bone
  • Adipose tissues
  • Skeletal muscle

    • Gluconeogenesis allows the use of which substrate during extended exercise?

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

    What role does gluconeogenesis play in metabolic acidosis?

    <p>Allows excretion of protons by the kidneys</p> Signup and view all the answers

    Which process contributes to glucose generation from intermediates of the TCA cycle?

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

    Which deficiency is closely related to the impact on gluconeogenesis?

    <p>Multiple Carboxylase Deficiency</p> Signup and view all the answers

    During periods of low carbohydrate intake, which metabolic pathway becomes more active?

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

    Which of the following does NOT require a continuous glucose supply?

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

    What is the primary source for gluconeogenesis?

    <p>Amino acids</p> Signup and view all the answers

    What is the primary location for gluconeogenesis under normal conditions?

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

    Which of the following compounds can serve as gluconeogenic precursors?

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

    During starvation, which organ may contribute up to 50% of the glucose produced through gluconeogenesis?

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

    What is the first step in the gluconeogenic pathway?

    <p>Pyrvate Carboxylation</p> Signup and view all the answers

    Which enzyme is involved in the conversion of Fructose 1,6-Bisphosphate to Fructose 6-Phosphate?

    <p>Fructose bisphosphatase</p> Signup and view all the answers

    What is a major substrate for gluconeogenesis derived from triglycerides?

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

    Which metabolic condition would most likely increase gluconeogenesis in the kidneys?

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

    What is one of the final steps in the gluconeogenic pathway after the conversion of G6P?

    <p>Dephosphorylation to Glucose</p> Signup and view all the answers

    What are ketogenic compounds primarily used for in metabolism?

    <p>Energy production through ketogenesis</p> Signup and view all the answers

    Which of the following mechanisms does glucagon NOT utilize to stimulate gluconeogenesis?

    <p>Inhibition of lipolysis</p> Signup and view all the answers

    What effect does glucagon have on fructose 2,6-bisphosphate levels?

    <p>It lowers fructose 2,6-bisphosphate levels</p> Signup and view all the answers

    How does glucagon induce covalent modification of enzyme activity?

    <p>By elevating cAMP levels</p> Signup and view all the answers

    What role does fructose 2,6-biphosphate play in glucose metabolism?

    <p>It serves as an allosteric inhibitor of fructose 1,6-bisphosphatase.</p> Signup and view all the answers

    Which statement is true regarding insulin's role in gluconeogenesis?

    <p>Insulin suppresses the synthesis of gluconeogenic enzymes</p> Signup and view all the answers

    Where does glucose 6-phosphate dephosphorylation primarily occur?

    <p>In the liver, kidneys, and small intestinal epithelial cells.</p> Signup and view all the answers

    Which hormones stimulate the synthesis of enzymes needed for gluconeogenesis?

    <p>Glucagon, epinephrine, and glucocorticoids</p> Signup and view all the answers

    Why can't glucose 6-phosphate derived from muscle glycogen yield free glucose?

    <p>Muscle cells do not contain glucose 6-phosphatase.</p> Signup and view all the answers

    What is the role of fructose 1,6-bisphosphatase in gluconeogenesis?

    <p>It catalyzes the conversion of fructose 1,6-bisphosphate to fructose 6-phosphate</p> Signup and view all the answers

    What is the effect of glucagon on fructose 2,6-biphosphate levels?

    <p>It decreases the concentration of fructose 2,6-biphosphate.</p> Signup and view all the answers

    Which enzyme's activity is inhibited by increased fructose 2,6-bisphosphate levels?

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

    Which enzyme is responsible for the irreversible step in gluconeogenesis that fructose 2,6-biphosphate inhibits?

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

    What is the primary impact of glucagon on pyruvate kinase activity?

    <p>It converts pyruvate kinase to its inactive form</p> Signup and view all the answers

    How does fructose 2,6-biphosphate serve as an example of reciprocal control?

    <p>It has opposing effects on enzymes in glycolysis and gluconeogenesis.</p> Signup and view all the answers

    What is one of the key functions of glucagon in relation to glycolysis?

    <p>Stimulates gluconeogenesis to bypass glycolytic steps</p> Signup and view all the answers

    Which metabolic pathway does fructose 2,6-biphosphate inhibit?

    <p>Gluconeogenesis.</p> Signup and view all the answers

    Which of the following statements about covalent modification in gluconeogenesis is correct?

    <p>It mainly involves phosphorylation and dephosphorylation processes</p> Signup and view all the answers

    What is the consequence of fructose 2,6-biphosphate concentration decreasing?

    <p>Enhanced gluconeogenic activity.</p> Signup and view all the answers

    What metabolic effect does the presence of fructose 2,6-biphosphate have on glucose 6-phosphatase?

    <p>It inhibits its activity.</p> Signup and view all the answers

    Which factor has a prominent influence on the rate of hepatic glucose synthesis?

    <p>Availability of gluconeogenic precursors</p> Signup and view all the answers

    What is the result of decreased insulin levels in the context of gluconeogenesis?

    <p>Increased mobilization of amino acids from muscles</p> Signup and view all the answers

    What causes the accumulation of acetyl CoA during starvation?

    <p>Excessive lipolysis in adipose tissue</p> Signup and view all the answers

    Which enzyme is inhibited by elevated AMP levels?

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

    What effect does acetyl CoA have in gluconeogenesis when it accumulates in the liver?

    <p>Allosteric activation of pyruvate carboxylase</p> Signup and view all the answers

    What is the effect of AMP elevation on metabolic pathways?

    <p>Activation of pathways that oxidize nutrients for energy</p> Signup and view all the answers

    Study Notes

    Overview of Gluconeogenesis

    • Gluconeogenesis is the synthesis of carbohydrates from noncarbohydrate precursors.
    • Primarily occurs in the liver (85-95% of glucose production); kidneys contribute 10%, especially during starvation or metabolic acidosis.

    Substrates for Gluconeogenesis

    • Key gluconeogenic precursors include lactate, pyruvate, alanine, glycerol (from triglycerides), alpha-keto acids, and specific amino acids.

    Pathway Steps

    • Begins with pyruvate carboxylation.
    • Oxaloacetate (OAA) is transported to the cytosol.
    • Cytosolic OAA undergoes decarboxylation.
    • Conversion of phosphoenolpyruvate (PEP) to fructose 1,6-bisphosphate (F1,6-BP) occurs.
    • Fructose 1,6-BP is dephosphorylated to fructose 6-phosphate (F6P).
    • Glucose 6-phosphate (G6P) is dephosphorylated to yield free glucose.

    Regulation of Gluconeogenesis

    • Hormonal regulation involves glucagon, insulin, and epinephrine which influence enzyme activity.
    • Non-hormonal regulation is dependent on substrate availability and allosteric effectors.

    Hormonal Regulation

    • Glucagon stimulates gluconeogenesis via:
      • Lowering fructose 2,6-bisphosphate levels, activating fructose 1,6-bisphosphatase and inhibiting phosphofructokinase (PFK).
      • Covalent modification of enzymes, converting pyruvate kinase to an inactive form.
      • Inducing enzyme synthesis for gluconeogenesis enzymes while suppressing glycolytic enzymes (hexokinase, PFK, and pyruvate kinase).
    • Insulin suppresses gluconeogenesis while promoting glycolysis.

    Non-Hormonal Regulation

    • Substrate availability is crucial; decreased insulin levels lead to amino acid mobilization for carbon skeletons in gluconeogenesis.
    • Allosteric activation occurs when there is an accumulation of acetyl CoA from fatty acid oxidation during starvation.
    • AMP serves as an allosteric inhibitor of fructose 1,6-bisphosphatase, stimulating PFK and energy-producing pathways.

    Functions of Gluconeogenesis

    • Generates glucose from glycolysis intermediates, fatty acids, or TCA cycle products.
    • Maintains blood sugar levels during starvation or low carbohydrate intake.
    • Excretes protons during metabolic acidosis.
    • Utilizes dietary protein in carbohydrate pathways.
    • Uses lactate during prolonged exercise.

    Continuous Glucose Requiring Tissues

    • Essential organs and tissues include the brain, lens and cornea of the eye, red blood cells (RBCs), testes, renal medulla, and exercising muscle.

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    Description

    This quiz dives into the process of gluconeogenesis, the vital synthesis of carbohydrates from noncarbohydrate precursors. You'll explore the key substrates, pathway steps, and the regulatory mechanisms that govern this metabolic pathway.

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