Dehydrogenases and Redox Potential
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Questions and Answers

Which of the following statements about peroxidases is true?

  • They are used to form hydrogen peroxide from water.
  • Their main function is to increase the levels of superoxide.
  • They are found exclusively in plant cells.
  • They are formed when reduced flavins are reoxidized. (correct)

    • What role does superoxide dismutase serve in aerobic organisms?

  • It catalyzes the formation of hydrogen peroxide.
  • It directly reduces oxygen to water.
  • It produces reactive oxygen species.
  • It protects against oxidative stress by converting superoxide. (correct)

    • Where are the components of the electron transport chain located?

  • In the cytoplasm
  • In the inner mitochondrial membrane (correct)
  • Within the outer mitochondrial membrane
  • In the nuclear membrane

    • Which complex in the electron transport chain is not a proton pump?

    <p>Complex II</p> Signup and view all the answers

    What is the final electron acceptor in the electron transport chain?

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

    Which component of peroxidases uses hydrogen peroxide as both an electron donor and acceptor?

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

    Glutathione peroxidase primarily protects what part of the cell?

    <p>RBC membrane</p> Signup and view all the answers

    What is the primary function of the electron transport chain?

    <p>Collect and transport reducing equivalents</p> Signup and view all the answers

    What is the primary function of oxygenases in biochemical reactions?

    <p>Catalyzing the incorporation of oxygen into the substrate molecule</p> Signup and view all the answers

    Which type of oxygenase incorporates both atoms of molecular oxygen into the substrate?

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

    What does a more negative Eo value indicate about a substance's ability to participate in redox reactions?

    <p>It is a better reductant.</p> Signup and view all the answers

    Which of the following statements accurately describes dehydrogenases?

    <p>They transfer hydrogen from one substrate to another.</p> Signup and view all the answers

    What type of oxygenase is also known as a mixed-function oxidase?

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

    In terms of redox potential, which of the following statements is true?

    <p>The more positive the Eo, the better the oxidant.</p> Signup and view all the answers

    What are the products formed by the action of monooxygenases?

    <p>Hydroxylated products</p> Signup and view all the answers

    Which of the following examples is a dioxygenase?

    <p>Homogentisate dioxygenase</p> Signup and view all the answers

    What type of coenzymes do pyridine-linked dehydrogenases utilize?

    <p>Derivatives of niacin.</p> Signup and view all the answers

    What is the primary function of dehydrogenases in cell metabolism?

    <p>To facilitate ATP generation via oxidation.</p> Signup and view all the answers

    Which of the following molecules is not considered an electron carrier in the inner mitochondrial membrane?

    <p>L-Tryptophan</p> Signup and view all the answers

    What distinguishes dioxygenases from monooxygenases?

    <p>The number of oxygen atoms incorporated into the substrate</p> Signup and view all the answers

    Which characteristic of a reductant is indicated by a more negative Eo?

    <p>It is better at donating electrons.</p> Signup and view all the answers

    What advantage do reducing equivalents provide in oxidative processes?

    <p>They allow oxidative processes to occur in the absence of oxygen.</p> Signup and view all the answers

    Which of these is not one of the electron carriers found in the electron transport assembly?

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

    What role do components of the electron transport chain (ETC) play concerning dehydrogenases?

    <p>They facilitate the transfer of reducing equivalents.</p> Signup and view all the answers

    Which complex in the electron transport chain is NOT considered a proton pump?

    <p>Complex II</p> Signup and view all the answers

    What is the role of CoQ in the electron transport chain?

    <p>It transfers electrons between complexes.</p> Signup and view all the answers

    Which of the following components serves as the prosthetic group in complex I?

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

    What type of proteins are found in complexes I, II, and III that are involved in electron transfer?

    <p>Iron-sulfur proteins</p> Signup and view all the answers

    During oxidative phosphorylation, which molecule is phosphorylated to form ATP?

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

    Which iron state is reduced to donate electrons to cytochrome c?

    <p>Ferrous iron (Fe2+)</p> Signup and view all the answers

    What is cytochrome b's role in complex III?

    <p>It transfers electrons from CoQH2.</p> Signup and view all the answers

    Which vitamin is a precursor for the flavoprotein FAD?

    <p>Vitamin B2</p> Signup and view all the answers

    What is the role of cytochrome c in the electron transport chain?

    <p>It links complex III to complex IV.</p> Signup and view all the answers

    Which type of iron is cytochrome b converted back to after being oxidized?

    <p>Fe3+</p> Signup and view all the answers

    Which enzyme is NOT an example of a NAD-linked dehydrogenase?

    <p>Succinate dehydrogenase</p> Signup and view all the answers

    What does FADH2 carry compared to NADH?

    <p>Two electrons and two H+ ions</p> Signup and view all the answers

    Which of the following correctly characterizes Fe2+ in cytochrome c?

    <p>It is oxidized to Fe3+.</p> Signup and view all the answers

    What is a characteristic of complex III in the context of the electron transport chain?

    <p>It functions as a proton pump.</p> Signup and view all the answers

    What products does reduced NADH generate during metabolic pathways?

    <p>Electrons and protons</p> Signup and view all the answers

    Which enzyme is associated with the beta oxidation pathway?

    <p>Hydroxyacyl CoA dehydrogenase</p> Signup and view all the answers

    Study Notes

    Dehydrogenase

    • Measures a biological system's tendency to release or accept electrons
    • Transfers hydrogen from one substrate to another, but not to oxygen
    • Expressed in volts (Eo)
      • More negative Eo: better reductant (electron donor)
      • More positive Eo: better oxidant (electron acceptor)

    Redox Potential in Mammalian Oxidation Systems

    • Types of Dehydrogenases:
      • Pyridine-linked dehydrogenases: use niacin derivatives as coenzymes
        • Nicotinamide adenine dinucleotide (NAD+)-linked dehydrogenases: involved in oxidative metabolic pathways generating ATP (e.g., peroxidases)
      • Flavoprotein dehydrogenases: use flavins (FMN & FAD) as coenzymes
        • FAD-linked dehydrogenases: involved in the citric acid cycle and fatty acid metabolism.
        • FMN-linked dehydrogenases: involved in the electron transport chain.

    Catalase

    • Uses hydrogen peroxide as both electron donor and acceptor to form water
    • Found in blood, bone marrow, mucous membranes, kidney, and liver
    • Destroys H2O2 formed by oxidases

    Oxygenases

    • Catalyze the direct transfer and incorporation of oxygen into a substrate molecule
    • Two Kinds of Oxygenases:
      • Dioxygenases: incorporate both atoms of molecular oxygen into the substrate (e.g. homogentisate, L-tryptophan, and hydroxyanthranilate dioxygenases)
      • Monooxygenases (Mixed-function oxidases/Hydroxylases): incorporate only one atom of molecular oxygen into the substrate.

    Superoxide Dismutase

    • Protects aerobic organisms against oxygen toxicity
    • Catalyzes the removal of superoxide by the following reaction: O2.- + O2.- + 2H+ → H2O2 + O2

    Electron Transport Chain (Respiratory Chain)

    • Found in the inner mitochondrial membrane
    • Collects and transports reducing equivalents (electrons) and directs them to their final reaction with oxygen to form water
    • Final acceptor of electrons is oxygen
    • Components:
      • Four large protein complexes (I, II, III, IV)
      • Three complexes serve as proton pumps (I, III, IV)
      • Complex II is not a proton pump
    • Coupled with oxidative phosphorylation
    • Components of ETC
      • Flavoproteins:
        • Components of complexes I & II
        • FMN: Prosthetic group of NADH dehydrogenase in complex I
        • FAD: Prosthetic group of succinate dehydrogenase in complex II
      • Iron-sulfur proteins (non-heme, Fe-S):
        • Found in complexes I, II, and III
        • Participate in single electron transfer reaction
    • Electron Carriers:
      • NAD: Derived from niacin (vitamin B3), active portion: nicotinamide ring, carries 2 electrons but only one H+, carrier of reduced NADH
        • Reduced NADH derived from NAD-linked dehydrogenases:
          • Isocitrate, α-ketoglutarate, & malate dehydrogenases of the Krebs cycle
          • Pyruvate dehydrogenase (linking glycolysis to the TCA cycle)
          • Hydroxyacyl CoA dehydrogenase of the fatty acid beta-oxidation pathway.
      • FAD: Derived from riboflavin (vitamin B2), active portion: isoalloxazine ring, carries 2 electrons and 2 H+, carrier of reduced FADH2
        • Reduced FADH2 derived from FAD-linked dehydrogenases:
          • Succinate dehydrogenase of the TCA cycle
          • Alpha-glycerophosphate shuttle dehydrogenase
          • Fatty acyl CoA dehydrogenase of beta oxidation

    Complex III

    • Cytochrome b: Representative cytochrome in complex III. Other cytochromes can be used as carriers
    • CoQH2 (reduced substrate): Transfers its electron to the ferric iron (Fe3+) of cytochrome b. CoQH2 is oxidized to CoQ upon transferring electrons
    • Fe3+ is reduced to ferrous iron (Fe2+) which serves as the electron donor and transfers the electron to ferric iron (Fe3+) of cytochrome c.
    • Fe2+ of cytochrome b converts back to Fe3+ while Fe3+ of cytochrome c is reduced to Fe2+
    • Cytochrome c links complex III to complex IV
    • Complex III is a proton pump.

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    Biochemistry Energy Metabolism Part 1 PDF

    Description

    Explore the roles of dehydrogenases in biological systems, including their function in transferring hydrogen and their significance in oxidation-reduction processes. Learn about different types of dehydrogenases, such as pyridine-linked and flavoprotein dehydrogenases, and their involvement in metabolic pathways. Dive into the intricacies of redox potential measurements expressed in volts.

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