Biochemistry: Ribose 5-Phosphate Formation
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Questions and Answers

What is the primary role of glutathione in red blood cells?

  • It enhances hemoglobin synthesis.
  • It maintains the reduced state of sulfhydryl groups of proteins. (correct)
  • It aids in the production of ATP.
  • It promotes the oxidation of lipids.

    • Which form of G6PD deficiency is characterized by normal enzyme stability but low activity levels?

  • Chronic Nonspherocytic Anemia
  • G6PD Mediterranean (correct)
  • Class III Deficiency
  • Class I Deficiency

    • What is the outcome of the oxidation of sulfhydryl groups in proteins?

  • Protein denaturation and formation of Heinz bodies. (correct)
  • Enhanced cell membrane integrity.
  • Increased enzyme activity.
  • Improved red blood cell lifespan.

    • What happens to G6PD enzyme activity in the oldest red blood cells?

    <p>It decreases to the lowest level.</p> Signup and view all the answers

    Which factors can compromise the glutathione defense system in G6PD deficiency?

    <p>Presence of infections and certain drugs.</p> Signup and view all the answers

    What role does NADPH oxidase play in the immune response?

    <p>It converts molecular O2 to superoxide in phagocytic cells.</p> Signup and view all the answers

    Which components are present in the subunits of NADPH oxidase?

    <p>Cytochrome and flavin coenzymes</p> Signup and view all the answers

    What is one consequence of a genetic deficiency in NADPH oxidase?

    <p>Severe, persistent chronic pyogenic infections</p> Signup and view all the answers

    How is NADPH oxidase activated in the immune response?

    <p>Recognition by phagocyte receptors</p> Signup and view all the answers

    What type of infections are typically associated with Chronic Granulomatosis?

    <p>Chronic pyogenic infections</p> Signup and view all the answers

    During the respiratory burst, what is formed from the transfer of electrons via NADPH?

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

    What is a major result of phagocytosis by immune cells?

    <p>Internalization of microorganisms</p> Signup and view all the answers

    Which factor regulates the activity of NADPH oxidase?

    <p>Hormonal signals</p> Signup and view all the answers

    What does the formation of granulomas typically indicate in immune response?

    <p>Sequestration of bacteria that were not destroyed</p> Signup and view all the answers

    Which of the following is a correct sequence of events involving NADPH oxidase?

    <p>Phagocytosis &gt; NADPH oxidase activation &gt; Reactive oxygen species generation</p> Signup and view all the answers

    Which enzyme is responsible for transferring a 3-carbon unit from sedoheptulose 5-phosphate to G3P?

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

    What is the primary role of ribose 5-phosphate in cellular processes?

    <p>Nucleotide and nucleic acid synthesis</p> Signup and view all the answers

    Which compound is produced alongside NADPH through the conversion of glucose 6-phosphate?

    <p>Fructose-6-phosphate</p> Signup and view all the answers

    Which of the following reactions does NOT involve the enzyme transketolase?

    <p>Formation of ribose 5-phosphate from G3P</p> Signup and view all the answers

    What is the stoichiometric outcome of the pentose phosphate pathway starting from glucose 6-phosphate?

    <p>3 G6P + 6 NADP+ → 6 NADPH + 2 F6P + 3 CO2</p> Signup and view all the answers

    In a situation where there is a high demand for NADPH, which pathway is likely to be favored?

    <p>Pentose phosphate pathway</p> Signup and view all the answers

    What essential element is required by Glutathione Peroxidase for its function?

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

    Which of the following statements is false regarding erythrose 4-phosphate?

    <p>It requires a cofactor for its metabolism.</p> Signup and view all the answers

    Which of the following best describes the role of glutathione in detoxifying H2O2?

    <p>Reduces it to form water and oxidized glutathione</p> Signup and view all the answers

    What is a significant difference between transaldolase and transketolase in the pentose phosphate pathway?

    <p>Transaldolase transfers 3-carbon units, while transketolase transfers 2-carbon units.</p> Signup and view all the answers

    Which substrate is formed from the combination of xylulose 5-phosphate and erythrose 4-phosphate?

    <p>F6P</p> Signup and view all the answers

    What is the chemical composition of reduced glutathione?

    <p>ϒ-glutamylcysteinylglycine</p> Signup and view all the answers

    Which reactive oxygen species is formed from the partial reduction of molecular O2?

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

    What process regenerates reduced glutathione after it has been oxidized?

    <p>Utilization of NADPH via glutathione reductase</p> Signup and view all the answers

    What type of reaction does Glutathione Peroxidase primarily carry out?

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

    What is the product of oxidized glutathione undergoing reaction with other thiol groups?

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

    Which of the following radicals is least likely to form during the partial reduction of O2?

    <p>Nitroxyl radical</p> Signup and view all the answers

    What structural feature of reduced glutathione allows it to fulfill its function as an antioxidant?

    <p>Sulfhydryl group</p> Signup and view all the answers

    What is the main method by which glutathione detoxifies reactive oxygen species?

    <p>Reduction reactions</p> Signup and view all the answers

    What is a consequence of decreased G6PD activity in red blood cells?

    <p>Increased formation of oxidative stress</p> Signup and view all the answers

    Which of the following mutations would most likely show an alteration in kinetic properties?

    <p>Mutations causing decreased catalytic activity</p> Signup and view all the answers

    How does hemolysis correlate with G6PD activity in patients?

    <p>It directly correlates with residual enzyme activity</p> Signup and view all the answers

    What effect does impaired NADPH formation have on red blood cells?

    <p>Decreases resistance to oxidative stress</p> Signup and view all the answers

    What is a result of increased resistance to Falciparum malaria linked to G6PD mutations?

    <p>Improved ability to manage red blood cell longevity</p> Signup and view all the answers

    Which factor does NOT affect the severity of the disease connected to G6PD deficiency?

    <p>Patient's age at diagnosis</p> Signup and view all the answers

    What structural aspect of an enzyme's active site is indicated in the content?

    <p>It's rarely affected by mutations</p> Signup and view all the answers

    Which of the following describes the impact of decreased stability of red blood cells due to G6PD mutations?

    <p>Increased hemolytic episodes</p> Signup and view all the answers

    Which biochemical factor is primarily affected by decreased G6PD activity?

    <p>NADPH formation</p> Signup and view all the answers

    How does the failure to maintain adequate reduced glutathione levels impact red blood cells?

    <p>Increases free radical accumulation</p> Signup and view all the answers

    Study Notes

    Formation of Ribose 5-Phosphate

    • Ribose 5-phosphate synthesizes from the transfer of a 3-carbon unit from sedoheptulose 5-phosphate to glyceraldehyde 3-phosphate (G3P).
    • Key intermediates include fructose-6-phosphate and erythrose-4-phosphate.
    • Enzyme involved: transaldolase, which does not require cofactors.
    • Xylulose 5-phosphate and erythrose 4-phosphate are converted to fructose 6-phosphate (F6P) and G3P using TPP-dependent transketolase.

    Summary of Reactions

    • Stoichiometry: 3 G6P + 6 NADP+ → 2 F6P + 3 CO2 + G3P + 6 NADPH + 6 H+.

    Regulation of the Pathway

    • Glutathione Peroxidase:
      • A selenium-requiring enzyme that reduces hydrogen peroxide (H2O2) to detoxify it.
      • Reduces oxidized glutathione (GSSG) back to reduced glutathione (GSH) using NADPH.

    Formation of Reactive Intermediates

    • Molecular oxygen, when partially reduced, creates reactive oxygen species such as superoxide and hydrogen peroxide.
    • Immune response:
      • Bacteria are recognized by immune cells leading to phagocytosis and oxidation of O2 to superoxide via NADPH oxidase in white blood cells.

    Genetic Deficiencies of NADPH Oxidase

    • Chronic Granulomatosis:
      • A severe condition leading to persistent infections and granuloma formation.
      • Complications from chronic hemolysis can decrease life span.
      • Some mutations do not affect enzyme structure but change kinetic properties.

    Role of G6PD in RBCs

    • Reduced G6PD activity results in impaired NADPH formation.
    • Insufficient reduced glutathione increases oxidative stress sensitivity, leading to red blood cell instability and hemolysis.
    • G6PD variants influence the severity of the condition, with class III (G6PD A-) showing moderate deficiencies in reticulocytes but not old RBCs.

    Variants of G6PD Deficiency

    • G6PD Mediterranean:
      • Class II deficiency with normal enzyme stability but very low activity.
    • Class I mutations can cause Chronic Nonspherocytic Anemia.

    Hemolysis Mechanisms

    • Integrity of red blood cells requires ATP, NADH, and NADPH from the pentose phosphate pathway (PPP).
    • Compromised glutathione defense systems due to G6PD deficiency are particularly vulnerable to infections, drugs, and dietary factors like fava beans.

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    Description

    This quiz covers the formation of Ribose 5-Phosphate, focusing on the transfer of 3-carbon units from sedoheptulose 5-phosphate to G3P. It also examines key intermediates of glycolysis such as fructose-6-phosphate and erythrose-4-phosphate, as well as the role of the enzyme transaldolase in this process.

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