Glycolysis and Hexokinase Enzymes
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Questions and Answers

What is the effect of ATP on pyruvate kinase?

  • Competitively inhibits pyruvate kinase
  • Non-competitively inhibits pyruvate kinase
  • Allosterically activates pyruvate kinase
  • Allosterically inhibits pyruvate kinase (correct)
  • What is the role of acetyl-CoA in glucose metabolism?

  • Allosterically inhibits pyruvate dehydrogenase (correct)
  • Allosterically stimulates pyruvate carboxylase
  • Inhibits PEP carboxykinase
  • Inhibits pyruvate carboxylase
  • What is the role of insulin in glucose metabolism?

  • Inhibits hexokinase II
  • Decreases expression of pyruvate kinase
  • Inhibits phosphofructokinase-1
  • Increases expression of hexokinase II (correct)
  • What is the effect of fatty acids on gluconeogenesis?

    <p>Has no effect on gluconeogenesis</p> Signup and view all the answers

    What is the function of PEP carboxykinase in glucose metabolism?

    <p>Essential for gluconeogenesis</p> Signup and view all the answers

    What is the effect of acetyl-CoA on pyruvate carboxylase?

    <p>Allosterically stimulates pyruvate carboxylase</p> Signup and view all the answers

    Which enzyme is essential for the conversion of glucose to lipids?

    <p>Acetyl-CoA carboxylase</p> Signup and view all the answers

    Which statement about insulin is true?

    <p>Increases expression of hexokinase II</p> Signup and view all the answers

    What is the role of NADH in glucose metabolism?

    <p>Inhibits the citric acid cycle</p> Signup and view all the answers

    Which enzyme is inhibited by ATP?

    <p>Pyruvate kinase</p> Signup and view all the answers

    Study Notes

    Hexokinase Isozymes

    • Hexokinase I, II, and III are inhibited by their product, glucose 6-phosphate
    • Hexokinase IV (glucokinase) in the liver is not inhibited by glucose 6-phosphate
    • Hexokinase IV has kinetic properties related to maintaining glucose homeostasis
    • Km of hexokinase IV is higher than the usual glucose concentration

    Regulation of Hexokinase IV

    • Regulatory protein anchors hexokinase IV inside the nucleus, segregating it from other glycolytic enzymes
    • Fructose 6-phosphate is an allosteric effector
    • Glucose causes dissociation of the regulatory protein

    Glycolysis and Gluconeogenesis

    • Glycolysis and gluconeogenesis are not identical pathways running in opposite directions
    • 3 glycolysis reactions are essentially irreversible in vivo and cannot be used in gluconeogenesis; must be bypassed with exergonic reactions
    • Gluconeogenesis and glycolysis share several steps, but are reciprocally regulated

    Mechanisms of Flux Control

    • Allosteric control: effectors (substrates, products, or coenzymes) in the pathway, but not necessarily of the enzyme in question (feedback regulation)
    • Covalent modification: breaking or formation of bonds alters enzyme activity
    • Substrate cycles: two opposing reactions catalyzed by different enzymes, independently controlled
    • Genetic control: amount of enzyme present is increased by protein synthesis

    Regulation of Glycolysis and Gluconeogenesis

    • Simultaneous operation of both pathways at each of the three bypass points would consume ATP without accomplishing chemical or biological work
    • Regulation prevents wasteful operation of both pathways at the same time

    Regulation of Pyruvate Carboxylase and PEP Carboxykinase

    • Gluconeogenesis is regulated at the level of FBPase-1, pyruvate carboxylase, and PEP carboxykinase
    • Pyruvate can be converted to glucose (and glycogen) via gluconeogenesis or oxidized to acetyl-CoA for energy

    Transcriptional Regulation

    • Insulin transcriptionally regulates more than 150 genes, including hexokinase II, hexokinase IV, phosphofructokinase-1 (PFK-1), and others
    • Changes in gene expression play a crucial role in glucose metabolism

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    Description

    This quiz covers the enzymes involved in glycolysis, specifically hexokinase isozymes and their kinetic properties. It also explores how they interact with glucose 6-phosphate.

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