Glutathione Peroxidase Quiz
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Questions and Answers

What is the primary function of Glutathione Peroxidase in relation to hydrogen peroxide?

  • To promote the formation of superoxide
  • To increase the production of hydrogen peroxide
  • To chemically detoxify hydrogen peroxide (correct)
  • To convert hydrogen peroxide into molecular oxygen

    • Which amino acid is specifically involved in the structure of reduced glutathione?

  • Glutamine
  • Tyrosine
  • Methionine
  • Cysteine (correct)

    • Which of the following describes the relationship between NADPH and glutathione reductase?

  • NADPH is a source of reducing electrons for regenerating reduced glutathione (correct)
  • NADPH is used to oxidize glutathione
  • NADPH inhibits the action of glutathione reductase
  • NADPH directly binds to hydrogen peroxide

    • What is the consequence of the oxidation of the sulfhydryl group in glutathione?

    <p>It results in the formation of a disulfide bond</p> Signup and view all the answers

    What type of electrons are involved in the biradical state of molecular oxygen?

    <p>Unpaired electrons with parallel spins</p> Signup and view all the answers

    Which of the following reactive species is NOT formed from the partial reduction of molecular oxygen?

    <p>Carbon dioxide</p> Signup and view all the answers

    What role does selenium play in the function of Glutathione Peroxidase?

    <p>It is a necessary cofactor</p> Signup and view all the answers

    How does glutathione contribute to cellular defense against oxidative stress?

    <p>By detoxifying reactive oxygen species through oxidation</p> Signup and view all the answers

    What happens to glutathione after it detoxifies hydrogen peroxide?

    <p>It is converted to an oxidized form and must be regenerated</p> Signup and view all the answers

    Which of the following describes a purpose of modifying a drug or xenobiotic?

    <p>Making a toxic compound more soluble for excretion</p> Signup and view all the answers

    What role do hydroxyl groups play in the detoxification process?

    <p>They serve as conjugation sites to increase solubility.</p> Signup and view all the answers

    Which of the following is NOT a feature of the oxygen-dependent bacterial killing mechanisms?

    <p>Utilization of lysosomal enzymes for pH changes</p> Signup and view all the answers

    Which white blood cells are primarily involved in the phagocytic process?

    <p>Neutrophils, Macrophages, and Monocytes</p> Signup and view all the answers

    What is the main product generated by the myeloperoxidase system during the bacterial killing process?

    <p>Hypochlorous Acid</p> Signup and view all the answers

    How do oxygen-independent systems contribute to bacterial killing?

    <p>Through pH changes in the phagolysosome and lysosomal enzymes</p> Signup and view all the answers

    Which compound is generated from superoxide through enzymatic conversion in the bacterial killing mechanisms?

    <p>Hydrogen Peroxide</p> Signup and view all the answers

    What is the function of reactive oxygen species produced during phagocytosis?

    <p>To directly kill engulfed pathogens</p> Signup and view all the answers

    Which xenobiotic modification leads to increased solubility for excretion?

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

    What triggers the respiratory burst in neutrophils during phagocytosis?

    <p>Activation of NADPH oxidase</p> Signup and view all the answers

    What is the primary function of NADPH in red blood cells?

    <p>To provide reducing equivalents for various biochemical reactions</p> Signup and view all the answers

    What consequence results from a glucose 6-phosphate dehydrogenase defect?

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

    Which of the following enzymes is NOT directly involved in antioxidant defense against reactive oxygen species (ROS)?

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

    Where in the body is the highest activity of antioxidant enzymes typically found?

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

    What role does glutathione play in redox biology?

    <p>It is a nonenzymatic antioxidant</p> Signup and view all the answers

    The accumulation of oxidized glutathione (G-S-S-G) indicates what in cellular physiology?

    <p>Decreased NADPH availability</p> Signup and view all the answers

    Which of the following statements about cytochrome P450 enzymes is false?

    <p>They are absent in smooth muscle endoplasmic reticulum</p> Signup and view all the answers

    What effect does the nonreduction of oxidized glutathione have on red blood cells?

    <p>Causes membrane instability and potential lysis</p> Signup and view all the answers

    Superoxide dismutase and catalase work together in which of the following ways?

    <p>Superoxide dismutase catalyzes the conversion of O2- to H2O2, which is then converted to water by catalase.</p> Signup and view all the answers

    Which biological compartment is least likely to contain high levels of antioxidant enzymes?

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

    How does decreased G6PD activity affect red blood cells in terms of oxidative stress?

    <p>It diminishes the ability to detoxify free radicals and peroxides.</p> Signup and view all the answers

    What is the relationship between G6PD enzyme activity and the severity of the disease in patients?

    <p>Decreased enzyme activity is associated with greater disease severity.</p> Signup and view all the answers

    Which statement accurately reflects the role of G6PD in red blood cells?

    <p>G6PD helps maintain reduced glutathione levels.</p> Signup and view all the answers

    What is a consequence of mutant enzymes with altered kinetic properties due to G6PD mutations?

    <p>Decreased catalytic activity.</p> Signup and view all the answers

    How does a mutation leading to increased resistance to Falciparum Malaria impact G6PD status?

    <p>It may lead to mutations that result in reduced G6PD gene function.</p> Signup and view all the answers

    What is the effect of decreased NADPH formation due to reduced G6PD activity?

    <p>Reduced levels of reduced glutathione.</p> Signup and view all the answers

    What is the primary function of cGMP in vascular smooth muscle relaxation?

    <p>Decreases entry of Ca2+ into smooth muscle cells</p> Signup and view all the answers

    Which oxidant drug is NOT listed as a precipitating factor for hemolytic anemia in G6PD deficiency?

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

    Which substance is primarily synthesized by eNOS in endothelial cells?

    <p>Nitric oxide</p> Signup and view all the answers

    What is the expected time frame for hemolytic effects after the consumption of fava beans in G6PD deficient patients?

    <p>24-48 hours</p> Signup and view all the answers

    Which of the following is NOT a result of the activation of protein kinase G by cGMP?

    <p>Increased myosin light-chain activity</p> Signup and view all the answers

    Which class of drugs is associated with a hemolytic reaction in patients with G6PD deficiency?

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

    What is the main mechanism of action for sildenafil citrate in the body?

    <p>Inhibits phosphodiesterase that deactivates cGMP</p> Signup and view all the answers

    What is primarily responsible for the decrease in blood pressure after the action of vasodilator nitrates?

    <p>Release of nitric oxide resulting in smooth muscle relaxation</p> Signup and view all the answers

    Which of the following conditions is aggravated by G6PD deficiency?

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

    What is the consequence of protein kinase G activation in smooth muscle cells?

    <p>Inhibition of Ca2+ channels</p> Signup and view all the answers

    Study Notes

    Glutathione Peroxidase

    • Selenium-dependent enzyme crucial for reducing hydrogen peroxide (H2O2).
    • H2O2 is a reactive oxygen species formed from the incomplete reduction of molecular oxygen.
    • Transitions between reduced glutathione (a tripeptide) and oxidized glutathione utilizing glutathione reductase and NADPH.

    Production of Glutathione

    • The reduced form of glutathione (G-SH) can be oxidized to its disulfide form (G-S-S-G).
    • The hexose monophosphate (HMP) pathway provides necessary NADPH for regeneration of reduced glutathione.
    • Glucose 6-phosphate dehydrogenase deficiency linked to low NADPH leads to oxidized glutathione accumulation, causing H2O2 buildup and red blood cell instability.

    Antioxidant Enzymes

    • Superoxide dismutase and catalase also play significant roles in antioxidant defense.
    • NADPH supplies reducing equivalents necessary for cytochrome P450 monooxygenase activity in liver metabolism.
    • Antioxidant enzymes are predominantly active in the liver, adrenal glands, and kidneys.

    Detoxification Mechanisms

    • Glutathione acts as a nonenzymatic antioxidant detoxifying xenobiotics like drugs and pollutants.
    • Modifications can activate/inactivate drugs and enhance water solubility for excretion.
    • Conjugation sites introduced through hydroxyl groups facilitate increased solubility, aiding in elimination.

    Phagocytosis and Reactive Oxygen Species (ROS)

    • White blood cells (neutrophils, macrophages, monocytes) utilize phagocytosis to ingest pathogens and debris.
    • Reactive oxygen species are generated during the respiratory burst, crucial for microbial killing.
    • Mechanisms include activation of NADPH oxidase leading to superoxide production followed by H2O2 and myeloperoxidase activity generating hypochlorous acid (HOCl).

    G6PD Deficiency Implications

    • Most individuals with G6PD deficiency remain asymptomatic, clinical symptoms arise under stress factors like oxygen exposure or specific drugs.
    • Drugs like sulfonamides, chloroquine, and fava beans can precipitate hemolytic anemia due to reduced antioxidant capacity.
    • Mutations affecting G6PD can result in varied enzyme activity, stability, and altered affinity for substrates.

    Importance of G6PD in Red Blood Cells

    • G6PD is essential for maintaining NADPH levels, which protects red blood cells from oxidative stress.
    • Deficiency leads to inadequate reduced glutathione, making RBCs prone to oxidative damage and hemolysis.
    • Severity of hemolytic episodes correlates with the level of G6PD enzyme activity present in red blood cells.

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    Test your knowledge on glutathione peroxidase, a selenium-dependent enzyme important for reducing hydrogen peroxide. This quiz covers its function, structure, and role in oxidative stress. Perfect for students of biochemistry and cell biology.

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