Cellular Energy Production and Oxygen
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Questions and Answers

In the cellular process of energy production, what role does oxygen primarily fulfill?

  • It directly catalyzes the conversion of pyruvate to acetyl CoA.
  • It serves as a primary substrate for the biosynthesis of complex molecules.
  • It functions as the final electron acceptor in the electron transport chain. (correct)
  • It acts as a signaling molecule to regulate nutrient uptake.
  • During the process of oxidative phosphorylation, which molecules donate electrons to the electron transport chain?

  • Acetyl CoA and Citrate
  • NADH and FADH2 (correct)
  • Pyruvate and Lactate
  • Glucose and amino acids
  • Which of the following best describes the function of cytochrome oxidase?

  • It couples the oxidation of nutrients to the biosynthesis of steroids.
  • It binds oxygen and facilitates its reduction to water. (correct)
  • It transports fatty acids from the cytoplasm to the mitochondria.
  • It directly converts glucose into pyruvate
  • In the context of energy extraction from nutrients, which stage involves the complete transfer of energy to a usable form by cells?

    <p>Electron transport and oxidative phosphorylation (A)</p> Signup and view all the answers

    Besides its role in energy generation, which other process in human biology uses oxygen?

    <p>Biosynthesis of steroids and in the degradation of drugs and toxins (B)</p> Signup and view all the answers

    How many protons are pumped into the cytosol side by cytochrome reductase?

    <p>2 (D)</p> Signup and view all the answers

    Which molecule serves as an electron carrier that contains a haeme group?

    <p>Cytochrome c (C)</p> Signup and view all the answers

    What is the basic structure of the haeme?

    <p>A porphyrin ring with iron at its centre (C)</p> Signup and view all the answers

    Which of the following molecules can act as an electron donor or acceptor?

    <p>Haeme (D)</p> Signup and view all the answers

    What molecule does cytochrome c transfer electrons to?

    <p>Oxygen (B)</p> Signup and view all the answers

    What is another name for complex IV?

    <p>Cytochrome a and a3 (D)</p> Signup and view all the answers

    How many protons are pumped out into the cytosol side by complex IV?

    <p>4 (A)</p> Signup and view all the answers

    What is a key function of heme, other than in cytochromes?

    <p>To bind oxygen (B)</p> Signup and view all the answers

    What is the precursor for both haeme and cytochrome c?

    <p>Fe-Protoporphyrin-IX (C)</p> Signup and view all the answers

    Which protein complexes of the electron transport chain directly contribute to the establishment of a proton gradient across the inner mitochondrial membrane?

    <p>Complex I, III, and IV (A)</p> Signup and view all the answers

    What is the role of ubiquinone (Q) in the electron transport chain?

    <p>To act as a mobile electron carrier between Complex I, Complex II and Complex III (C)</p> Signup and view all the answers

    The transfer of electrons through NADH-Q reductase (Complex I) results in the pumping of how many protons across the inner mitochondrial membrane for every molecule of NADH oxidized?

    <p>4 protons (D)</p> Signup and view all the answers

    Which of the following best characterises the electron flow through the electron transport chain?

    <p>NADH → Complex I → Q → Complex III → Cytochrome c → Complex IV → O2 (B)</p> Signup and view all the answers

    What thermodynamic property provides the driving force for oxidative phosphorylation?

    <p>The electron transfer potential of NADH or FADH2 relative to oxygen (C)</p> Signup and view all the answers

    What is a major difference between Complex I and Complex II in the electron transport chain?

    <p>Complex I pumps protons across the inner mitochondrial membrane, while Complex II does not (D)</p> Signup and view all the answers

    How many kilocalories (kcal) are approximately required for the synthesis of each mole of ATP?

    <p>7.3 kcal (A)</p> Signup and view all the answers

    What is the role of cytochrome c in the electron transport chain, based on the given reaction?

    <p>It transitions between $Fe^{2+}$ and $Fe^{3+}$ states, accepting electrons. (A)</p> Signup and view all the answers

    Which of the following inhibitors blocks the NADH-Q reductase complex?

    <p>Rotenone and amytal (D)</p> Signup and view all the answers

    According to the chemiosmotic hypothesis, what is the primary role of the proton-motive force?

    <p>To drive the synthesis of ATP by the ATPase complex. (D)</p> Signup and view all the answers

    Which component of the ATP synthase, as described, is sensitive to oligomycin?

    <p>The stalk between Fo and F1 (C)</p> Signup and view all the answers

    How many protons are translocated through the ATP synthase for the formation of one molecule of ATP, based on the description?

    <p>3 (D)</p> Signup and view all the answers

    What is the function of the ATP-ADP translocase?

    <p>To facilitate the exchange of ATP out of the mitochondria and ADP into the mitochondria. (A)</p> Signup and view all the answers

    How many protons are consumed in the process of transporting one ATP molecule out of the mitochondria, according to the text?

    <p>1 (A)</p> Signup and view all the answers

    Which of the following does NOT directly inhibit a component of the electron transport chain as described in the text?

    <p>Oligomycin (B)</p> Signup and view all the answers

    Approximately, what percentage of the energy yield from electron transfer is used for the transport of ATP out of the mitochondria?

    <p>25% (B)</p> Signup and view all the answers

    Study Notes

    Role of Oxygen in Energy Production

    • Oxygen is crucial for extracting energy from major nutrients.
    • Cells absorb oxygen and nutrients, and mitochondria further use nutrient metabolites and oxygen.
    • Cytochromes are oxygen-binding proteins.
    • Electrons from nutrient metabolites are transferred to mobile carriers.
    • Cytochrome Oxidase binds and reduces oxygen.
    • Oxygen reduction is vital for ATP synthesis.

    Stages in Extracting Energy

    • Energy extraction from nutrients involves three stages:
      • Stage I: Digestion, absorption, transport
      • Stage II: Breakdown of small molecules into key metabolites
      • Stage III: Complete transfer of energy to a usable form for cells
    • The process involves fats, polysaccharides, and proteins as fuel molecules.
    • These macronutrients are converted to smaller molecules like Acetyl CoA.

    Reactions Requiring Oxygen

    • Oxygen acts as an electron sink in energy generation.
    • It extracts high-potential electrons from NADH and FADH2, which are generated by oxidizing carbohydrates, amino acids, and fatty acids.
    • Oxygen is also involved in the biosynthesis of steroids and biodegradation of drugs/toxins.

    Metabolism of Major Nutrients and Energy Extraction

    • Nutrient metabolism starts in the cytoplasm.
    • Glucose and amino acids are converted.

    Role of Mitochondria

    • Mitochondria are crucial in ATP production.
    • Oxidative phosphorylation is the process where mitochondria produce ATP by transferring electrons from NADH or FADH2 to oxygen.

    Oxidative Phosphorylation in Eukaryotes

    • Oxidative phosphorylation relies on protein complexes located in the inner mitochondrial membrane.
    • These complexes, including the electron transport chain and ATP synthase, are located in the inner membrane.
    • Oxygen accepts the energy-depleted electrons and combines with hydrogen atoms to form water.

    Flow of Electrons

    • The flow of electrons from NADH or FADH2 to oxygen triggers the pumping of protons outside the mitochondrial matrix.
    • This creates a pH gradient that helps generate ATP (Chemiosmotic hypothesis).

    Components of the Electron Transport Chain

    • The electron transport chain (ETC) includes 3 oxido-reductase complexes that function as proton pumps (I, III, and IV).
    • These complexes use NADH-Q reductase, cytochrome reductase, and cytochrome oxidase.
    • Two electron carriers, ubiquinone (Q) and cytochrome c, are also involved.

    Driving Force for Oxidative Phosphorylation

    • The driving force behind oxidative phosphorylation is the transfer potential of NADH or FADH2 relative to oxygen.
    • The oxidation of NADH or FADH2 provides the energy to synthesize ATP.
    • Each ATP molecule requires approximately 7.3 kcal

    NADH-Q Reductase (Complex I)

    • This complex consists of 34 polypeptides, and has FMN and Fe-S prosthetic groups.
    • The flow of two electrons from NADH to QH2 through NADH-Q reductase pumps 4 protons from the matrix to the cytosol side of the inner membrane.

    Coenzyme Q (Ubiquinone)

    • It's a quinone derivative with a long isoprenoid tail, which functions as an electron carrier.
    • It exists in three forms: oxidized (Q), semiquinone intermediate (Q*), and reduced (QH2).

    Succinate-Q Reductase (Complex II)

    • Coenzyme Q also receives electrons from FADH2.
    • Electrons from FADH2 are transferred to Complex II and then to Q to enter the ETC.
    • Unlike complexes I, III, and IV, Complex II is not a proton pump.

    Cytochrome Reductase (Complex III) and Cytochrome C

    • Electrons flow from ubiquinone (Q) to Complex III and then to cytochrome c,
    • Two (2) protons are pumped out into the cytosol.
    • Cytochrome c is an electron carrier protein with heme.

    Haeme (Heme) Structure

    • Heme is a crucial part of cytochrome c, acting as an electron donor/acceptor in cytochromes.
    • It's also involved in oxygen binding in hemoglobin and cytochrome oxidase

    Cytochrome Oxidase (Complex IV)

    • Cytochrome c transfers electrons to oxygen.
    • Complex IV catalyzes the transfer of electrons from cytochrome c to oxygen.
    • Four protons are pumped out to the cytosol during this process.

    Inhibitors of Electron Transfer

    • Inhibitors like rotenone, amytal, and antimycin A block the ETC, preventing electron flow.
    • Cyanide, N3, and CO inhibit cytochrome oxidase (complex IV).

    Chemiosmotic Hypothesis

    • Electron transfer through the respiratory chain pumps protons from the matrix to the cytosol.
    • This generates a proton-motive force.
    • This force drives ATP synthesis by ATPase in the mitochondria.

    ATP Synthase

    • ATP synthase is an enzyme complex, composed of proton-conducting Fo and a catalytic F1 units.
    • The Fo containing stalk has several proteins to increase sensitivity to oligomycin.

    Action of ATP Synthase

    • Proton flux through ATP synthase cause conformation changes in the enzyme for ATP formation.
    • translocation of three (3) protons through the synthase leads to the formation of one ATP.

    ATP-ADP Translocase

    • The entry of ADP into mitochondria depends on ATP exit via ATP-ADP translocase.
    • It cost 1 proton to drive the transport of ATP in/out of mitochondria.
    • About 25% of energy from electron transfer is used for ATP transport

    Energy Yield in Electron Transfer

    • NADH-Q reductase pumps (4) protons.
    • Cytochrome reductase pumps (2).
    • Cytochrome oxidase pumps (4).
    • Synthesis of 1 ATP needs 3 protons.
    • Flow of 2 electrons from NADH to O2 leads to 10 protons pumped and generate 2.5 cytosolic ATP.
    • Flow of 2 electrons from FADH2 to O2 leads to 6 protons pumped and generate about 1.5 cytosolic ATP.

    ATP Yield from Complete Glucose Oxidation

    • Glycolysis gives about 2 ATP and 2 NADH
    • Converting 2 pyruvate into 2 acetyl CoA gives 2 NADH, and 2GTP
    • The Krebs Cycle (TCA cycle) gives 6NADH, 2FADH2, and 2GTP.

    Two Shuttle Systems for NADH

    • Glycerol 3-phosphate shuttle transfers electrons from NADH to FADH2.
    • Malate-aspartate shuttle transfers electrons from NADH to NADH, retaining the reducing potential.

    Uncoupling of Oxidative Phosphorylation

    • Uncouplers like DNP disrupt the coupling between electron transport and ATP synthesis by carrying protons across the membrane.
    • This dissipates the proton motive force.
    • Uncoupling increases oxidation and oxygen consumption.

    Uncoupling and Thermogenesis

    • Uncoupling is a way to generate heat to maintain body temperature in hibernating animals, newborns, and cold-adapted mammals.
    • Brown adipose tissue, rich in mitochondria, uses uncoupling protein UCP-1 to dissipate the proton gradient and create heat.

    UCP-1 and Thermogenesis

    • UCP-1 carries protons across the inner mitochondrial membrane, leading to thermogenesis.
    • Sympathetic nerve stimulation triggers the formation of free fatty acids, activating UCP-1 and creating heat.

    Cyanide Poisoning

    • Cyanide inhibits oxidative phosphorylation by blocking cytochrome oxidase.

    Opisthotonus in Tetanus

    • Opisthotonus is a symptom of tetanus characterized by spasm of axial muscles, causing the head, neck, and spinal column to arch backwards.

    Cyanide Poisoning: Treatment

    • General supportive care and oxygen.
    • GI decontamination methods to remove toxins.
    • Conversion of hemoglobin Fe2 to Fe3 can release cyanide from cytochrome oxidase and encourage metabolism of cyanide to thiocyanate.
    • Thiosulfate is used to catalyze the conversion of cyanide to less harmful thiocyanate.

    Mitochondria as a Source of Chemical Signals

    • Mitochondria release cytochrome c, triggering apoptosis (programmed cell death).
    • Problems with ETC enzymes can cause neurodegenerative disorders like Parkinson's disease.
    • Mitochondria produce reactive oxygen species, potentially contributing to aging and metabolic syndromes.

    Summary of Energy Extraction

    • Optimal energy extraction from nutrients relies on oxygen.
    • Blood circulation delivers oxygen and nutrients.
    • Mitochondria synthesize ATP using oxidative phosphorylation.
    • Electron release from nutrients drives proton pumping.
    • Proton gradient drives ATP synthesis, which is done by mobile proton carriers.
    • Complexes I and II provide connections between the Krebs cycle and the ETC.

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    Description

    Explore the essential role of oxygen in cellular energy production through oxidative phosphorylation. This quiz covers key components like electron transport chains, cytochrome functions, and energy extraction stages. Test your knowledge on molecules involved and their structures in the intricate process of cellular respiration.

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