Pentose Phosphate Pathway
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Questions and Answers

What is the role of Glucose-6-phosphate dehydrogenase (GPD) in the oxidative phase?

  • To synthesize pentose phosphate
  • To reduce NADPH to NADP+
  • To catalyze the first reaction of the oxidative phase (correct)
  • To convert glucose-6-phosphate to glycogen
  • What is the product of the oxidative phase that is converted to intermediates of glycolysis?

  • Glucose-6-phosphate
  • Pentose phosphate (correct)
  • CO2
  • NADPH
  • What is the role of NADPH+H in RBC membrane integrity?

  • To reduce hemoglobin
  • To synthesize cholesterol
  • To oxidize glutathione
  • To maintain the reduced state of thiol groups in proteins (correct)
  • What is the result of oxidation of thiol groups in hemoglobin?

    <p>Denaturation of proteins and precipitation of insoluble mass</p> Signup and view all the answers

    What is the function of reduced glutathione?

    <p>To reduce H2O2</p> Signup and view all the answers

    What is the result of oxidation of membrane proteins?

    <p>RBCs become rigid and are removed from circulation</p> Signup and view all the answers

    What is the byproduct of partial reduction of molecular oxygen?

    <p>H2O2</p> Signup and view all the answers

    What is the function of NADPH+H in reductive biosynthesis?

    <p>De Novo synthesis of fatty acids and steroids</p> Signup and view all the answers

    What is the function of glutathione peroxidase enzyme?

    <p>To remove excess H2O2 from the body</p> Signup and view all the answers

    What is the source of reducing electrons for glutathione reductase enzyme?

    <p>NADPH+H</p> Signup and view all the answers

    What is the primary source of NADPH in RBCs?

    <p>HMP-shunt pathway</p> Signup and view all the answers

    What is the effect of G6PD deficiency on RBCs?

    <p>Increased hemolysis</p> Signup and view all the answers

    Why do persons with G6PD deficiency show increased resistance to Malarial infection?

    <p>Due to the inability of the parasite to infect RBCs</p> Signup and view all the answers

    What is the function of glucose-6-phosphate dehydrogenase (G6PD) in the HMP-shunt pathway?

    <p>To produce NADPH</p> Signup and view all the answers

    What is the consequence of Favism in individuals with G6PD deficiency?

    <p>Hemolytic anemia</p> Signup and view all the answers

    Why is the HMP-shunt pathway important for RBC membrane integrity?

    <p>To produce NADPH for glutathione regeneration</p> Signup and view all the answers

    What is the function of NADPH in the regulation of RBC membrane integrity?

    <p>Maintains the reduced state of iron in hemoglobin</p> Signup and view all the answers

    What is the primary function of the pentose phosphate pathway?

    <p>To generate NADPH and pentose phosphates</p> Signup and view all the answers

    What is the role of NADPH in reductive biosynthesis?

    <p>To synthesize fatty acids and cholesterol</p> Signup and view all the answers

    What is the purpose of the Cori cycle?

    <p>To convert lactate to glucose</p> Signup and view all the answers

    What is the site of the pentose phosphate pathway?

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

    What is the role of NADPH in the regeneration of glutathione?

    <p>To reduce glutathione</p> Signup and view all the answers

    What is the function of the hexose monophosphate shunt?

    <p>To generate NADPH and pentose phosphates</p> Signup and view all the answers

    What is the percentage of glucose that enters the pentose phosphate pathway?

    <p>10%</p> Signup and view all the answers

    Study Notes

    Hexose Monophosphate (HMP) Shunt

    • About 10% of glucose per day enters this pathway, with the liver and RBCs metabolizing about 30% of glucose through this pathway.

    Phases of HMP Shunt

    Phase 1 (Oxidative Phase)

    • Glucose-6-phosphate is oxidized, generating 2 molecules of NADPH, 1 molecule of pentose phosphate, and liberating 1 molecule of CO2.
    • First reaction is catalyzed by Glucose-6-phosphate dehydrogenase (GPD), which is the rate-limiting step.

    Phase 2 (Non-Oxidative Phase)

    • Pentose phosphate is converted to intermediates of glycolysis.

    Functions of NADPH+H

    • Reductive biosynthesis (de novo synthesis of fatty acids and steroids).
    • Maintenance of RBC membrane integrity:
      • Reduced glutathione (GSH) helps maintain the reduced state of SH groups in proteins, including hemoglobin and membrane proteins.
      • Oxidation of thiol groups in hemoglobin leads to denaturation of proteins and precipitation of insoluble mass inside RBCs (Heinz bodies).
      • Oxidation of membrane proteins makes RBCs rigid, leading to removal from circulation by macrophages.
    • Reduction of glutathione:
      • NADPH+H reduces GS-SG into GSH, protecting thiol groups of cellular proteins from oxidation.
    • Reduction of H2O2:
      • NADPH+H reduces H2O2, a reactive oxygen species (ROS) that can cause damage to DNA, proteins, unsaturated lipids, and cell membranes.

    Deficiency of G6PD (Favism)

    • Favism is a hemolytic anemia, especially after ingestion of fava beans and certain compounds, such as antibiotics, anti-malarial, and antipyretics, which increase oxidative stress.
    • Deficiency of G6PD occurs in all cells, but is most severe in RBCs, where HMP-shunt is the only source of NADPH.
    • Other cells have alternative NADPH sources, such as NADPH-dependent malate dehydrogenase and NADPH-dependent isocitrate dehydrogenase.
    • Persons with G6PD deficiency show increased resistance to malarial infection.

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    Description

    This quiz covers the two phases of the pentose phosphate pathway, including the oxidative phase and non-oxidative phase. It involves the conversion of glucose-6-phosphate and the generation of NADPH and pentose phosphate.

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