Oxidative Phosphorylation Overview
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Questions and Answers

What is the primary function of Complex III in the electron transport chain?

  • To generate ATP directly
  • To reduce oxygen into water
  • To oxidize cytochrome c
  • To translocate additional protons to the intermembrane space (correct)

In what form of oxidation state can heme iron in cytochrome c exist?

  • Both ferrous (Fe3+) and ferric (Fe2+) (correct)
  • Neither ferrous nor ferric
  • Only ferrous (Fe3+)
  • Only ferric (Fe2+)

What is cytochrome c's role in the electron transport process?

  • It reduces ubiquinone to QH2
  • It carries a single electron from the cytochrome bc1 complex to cytochrome oxidase (correct)
  • It oxidizes oxygen to form water
  • It generates protons in the matrix

Which of the following components are found in mammalian cytochrome oxidase?

<p>Copper ions and heme groups (C)</p> Signup and view all the answers

How many protons are picked up from the matrix during the process of reducing one molecule of oxygen in Complex IV?

<p>Four protons (C)</p> Signup and view all the answers

What are the main reduced fuels that provide energy for ATP synthesis in cellular respiration?

<p>Carbohydrates, lipids, and amino acids (C)</p> Signup and view all the answers

What role do NADH and FADH2 play in oxidative phosphorylation?

<p>They act as electron donors in ATP synthesis. (C)</p> Signup and view all the answers

How is the energy required to convert ADP to ATP in oxidative phosphorylation provided?

<p>From the flow of protons down the electrochemical gradient (D)</p> Signup and view all the answers

Which of the following structures is NOT a component of a mitochondrion?

<p>Cell wall (C)</p> Signup and view all the answers

What is the significance of the cristae within the inner membrane of a mitochondrion?

<p>They increase surface area for electron transport chain complexes. (B)</p> Signup and view all the answers

Which theory explains the coupling of electron flow with proton movement to produce ATP?

<p>Mitchell's Chemiosmotic Theory (A)</p> Signup and view all the answers

Which component of the mitochondrion has the highest proton concentration during oxidative phosphorylation?

<p>Intermembrane space (C)</p> Signup and view all the answers

Which mechanism primarily drives the transport of protons against the electrochemical gradient in mitochondria?

<p>Coupling with electron transport chain reactions (A)</p> Signup and view all the answers

What is the total amount of ATP produced using the Malate Shuttle?

<p>38 ATP (B)</p> Signup and view all the answers

Which compounds primarily regulate the rate of oxidative phosphorylation?

<p>NADH and ADP/Pi (C)</p> Signup and view all the answers

How many ATP are produced from the oxidation of 2 NADH during glycolysis using the Malate Shuttle?

<p>6 ATP (C)</p> Signup and view all the answers

Which of the following is a measure of the energy status of a cell?

<p>Mass-Action Ratio (B)</p> Signup and view all the answers

What happens to the Mass-Action Ratio when energy is required in the cell?

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

What effect does high ATP concentration have on oxidative phosphorylation?

<p>Inhibits ATP production (C)</p> Signup and view all the answers

How many ATP are generated from the Krebs cycle per molecule of acetyl-CoA?

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

How does the intracellular concentration of ADP influence respiration rates?

<p>Decreases respiration rates when high (A)</p> Signup and view all the answers

What effect does the addition of cyanide (CN-) have on cellular respiration?

<p>It inhibits respiration and ATP synthesis. (B)</p> Signup and view all the answers

Which molecule is a known uncoupler that allows respiration without ATP synthesis?

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

What role does thermogenin play in brown adipose tissue?

<p>It provides heat through H+ flow. (D)</p> Signup and view all the answers

What is the primary function of the Malate-Aspartate Shuttle?

<p>To transport reducing equivalents (NADH) into the mitochondrial matrix. (B)</p> Signup and view all the answers

How does valinomycin contribute to the process of ATP synthesis?

<p>It generates a K+ electrochemical gradient. (A)</p> Signup and view all the answers

What is a consequence of the action of oligomycin?

<p>Inhibits ATP synthase activity. (C)</p> Signup and view all the answers

What is the end result of transferring reducing equivalents to the mitochondrial matrix via the Glycerol-3-Phosphate Shuttle?

<p>Formation of FADH2, resulting in a loss of energy. (B)</p> Signup and view all the answers

What is required for the translocation of an additional proton per ATP synthesized?

<p>Cotransport of substrates and products. (D)</p> Signup and view all the answers

What is primarily released from the mitochondria that triggers apoptosis?

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

Which of the following is correct regarding mitochondrial DNA?

<p>It is maternally inherited. (B)</p> Signup and view all the answers

What is a consequence of defects in oxidative phosphorylation?

<p>Low ATP levels in the cell. (C)</p> Signup and view all the answers

Which process occurs in the mitochondria?

<p>Protein synthesis using ribosomes (C)</p> Signup and view all the answers

What is the primary role of caspases in the cell?

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

Which of the following best describes the genetic coding of mitochondrial proteins?

<p>Most mitochondrial proteins are coded by nuclear DNA. (B)</p> Signup and view all the answers

What is the source of the proton motive force in mitochondria?

<p>Electron transport chain activity (D)</p> Signup and view all the answers

Which of the following accurately describes the role of mitochondrial ribosomes?

<p>They allow protein synthesis within mitochondria. (B)</p> Signup and view all the answers

What is the main role of Complex I in the electron transport chain?

<p>To transfer two electrons from NADH to ubiquinone (C)</p> Signup and view all the answers

How much energy is produced when transporting a pair of electrons from NADH to O2?

<p>220 kJ (D)</p> Signup and view all the answers

What happens to the four protons transported by NADH when it interacts with Complex I?

<p>They are pumped into the intermembrane space (C)</p> Signup and view all the answers

What is one key characteristic of Succinate Dehydrogenase (Complex II)?

<p>It has a dual role in both the citric acid cycle and electron transport chain (D)</p> Signup and view all the answers

What kind of reactions are involved in the transport of electrons through Complexes I to IV?

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

What is a function of uncouplers in the electron transport chain?

<p>To bypass the H+ flow through ATPase (C)</p> Signup and view all the answers

What is the result of the energetic difference in redox potential during electron transfer?

<p>Creation of a proton concentration gradient (A)</p> Signup and view all the answers

How many protons are transported into the intermembrane space for each NADH molecule processed by Complex I?

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

Flashcards

Oxidative Phosphorylation

Cellular process using energy from electron transfer to make ATP, the cell's energy currency.

Chemiosmotic Theory

Theory explaining ATP synthesis, where energy released from electron transport pumps protons against the gradient, creating a gradient used for ATP generation.

Electron Transport Chain

Sequence of protein complexes that transfer electrons to generate a proton gradient to make ATP.

ATP Synthesis

Process of making ATP from ADP and inorganic phosphate using the proton gradient generated by electron transport.

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Mitochondria

Organelle where oxidative phosphorylation (ATP production) occurs. It has a double membrane.

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Inner Mitochondrial Membrane

Highly impermeable membrane in mitochondria, location of the electron transport chain and proton gradient.

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Proton Gradient

Difference in proton concentration across a membrane, driving ATP synthesis.

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Reduced Cofactors

Molecules (like NADH and FADH2) carrying high-energy electrons from fuels for energy production.

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Electron Transport Chain (ETC)

A series of protein complexes in the mitochondria that transfer electrons from NADH and FADH2 to oxygen, creating a proton gradient.

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Complex I (NADH dehydrogenase)

Large mitochondrial protein complex that transfers electrons from NADH to ubiquinone (coenzyme Q), pumping protons across the inner mitochondrial membrane.

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Complex II (Succinate dehydrogenase)

A mitochondrial enzyme that catalyzes the oxidation of succinate to fumarate in the citric acid cycle and transfers electrons to ubiquinone (coenzyme Q) in the electron transport chain.

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Electron transfer inhibitors

Substances that block electron flow through the electron transport chain.

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Ubiquinone (Coenzyme Q)

A lipid-soluble electron carrier that accepts electrons from both Complex I and Complex II in the electron transport chain.

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ATP Production

Energy released from the electron transport chain is used to synthesize ATP via ATP synthase.

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Uncouplers

Molecules that disrupt the proton gradient, allowing protons to flow across the membrane without generating ATP.

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Cytochrome c

A mobile electron carrier that moves through the intermembrane space, carrying a single electron from the cytochrome bc1 complex to cytochrome oxidase.

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Cytochrome oxidase (Complex IV)

A membrane protein complex responsible for the final step in the electron transport chain, where oxygen is reduced to water.

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Heme a and a3

Two heme groups in cytochrome oxidase. The a3 group binds copper ions and accepts electrons from cytochrome c, ultimately reducing oxygen.

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CuA and CuB

Copper ions in cytochrome oxidase. CuA accepts electrons from cytochrome c, while CuB forms a binuclear center with heme a3 for oxygen reduction.

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Q-cycle

A process within Complex III where reduced quinones are oxidized, resulting in the translocation of protons across the membrane.

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Cyanide's effect on respiration

Cyanide blocks electron transfer between cytochrome oxidase (Complex IV) and oxygen, preventing both respiration and ATP synthesis.

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Succinate and ATP synthesis

Mitochondria provided with succinate can respire and produce ATP only when ADP and inorganic phosphate are present. This shows the need for these molecules in the process.

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Venturicidin/Oligomycin impact

Venturicidin and oligomycin inhibit ATP synthase, blocking both ATP production and respiration.

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What are uncouplers?

Molecules that allow respiration to continue without ATP synthesis. They disrupt the proton gradient, allowing protons to leak across the membrane.

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DNP: Proton transport

Dinitrophenol (DNP) is an uncoupler. It transports protons across the mitochondrial membrane, dissipating the energy.

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Substrate availability

The availability of molecules like NADH and ADP/Pi influences the speed of oxidative phosphorylation.

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Ionophores: Gradient disruptor

Ionophores disrupt ion gradients across membranes, uncoupling electron transport.

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ADP/Pi concentration

Higher levels of ADP and inorganic phosphate signal the need for more ATP production.

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Artificial gradient and ATP synthesis

An artificially imposed electrochemical gradient (produced by adding K+) can drive ATP synthesis even without an oxidizable substrate (fuel).

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Thermogenin: Brown fat's role

Thermogenin, an uncoupling protein in brown adipose tissue, allows proton flow without ATP synthesis, producing heat.

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Mass-Action Ratio

A measure of the cell's energy status, calculated as [ATP] / ([ADP] [Pi]). A high ratio indicates sufficient energy.

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Inhibition of OxPhos

High ATP levels can slow down oxidative phosphorylation by inhibiting various steps.

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NADH accumulation

When oxidative phosphorylation is slowed, NADH builds up due to reduced electron flow.

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Feedback Inhibition in Glycolysis

A regulatory mechanism where high levels of ATP or pyruvate inhibit key enzymes in glycolysis, such as PFK-1, to slow down glucose breakdown. This ensures energy production matches the cell's needs.

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Mitochondria's Role in Apoptosis

Mitochondria release cytochrome c into the cytosol when their membrane integrity is compromised, triggering a cascade of events leading to programmed cell death (apoptosis).

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Mitochondrial DNA

Circular DNA molecule within mitochondria that encodes essential proteins for respiration and energy production. It's maternally inherited.

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Mitochondrial Protein Synthesis

Mitochondria have their own ribosomes to synthesize some of their proteins, but most are encoded by nuclear DNA, synthesized in the cytosol, and imported into mitochondria.

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Mitochondrial Mutations and Diabetes

Defects in oxidative phosphorylation within mitochondria can lead to low ATP levels, preventing insulin secretion and causing a rare type of diabetes.

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Role of Cellular Respiration

Cellular respiration breaks down glucose to generate ATP, the cell's energy currency. It involves a series of reactions, including glycolysis, the citric acid cycle, and oxidative phosphorylation.

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Chemiosmotic Theory and Mitochondria

This theory explains how ATP is produced in mitochondria. Electron transport generates a proton gradient across the inner membrane, which is then used by ATP synthase to make ATP.

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Oxidative Phosphorylation: Main Processes

Oxidative phosphorylation takes place in mitochondria, involving the electron transport chain and ATP synthesis. It utilizes the energy from electron transfer to generate ATP.

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Electron Carriers in Oxidative Phosphorylation

Key electron carriers in oxidative phosphorylation include NADH, FADH2, ubiquinone (coenzyme Q), and cytochromes. They transfer electrons, releasing energy used for proton pumping.

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Electron Transport Complexes

Four protein complexes (I, II, III, IV) in the mitochondrial inner membrane carry out electron transport, pumping protons across the membrane to create a gradient.

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Proton Motive Force

The energy stored in the proton gradient generated by the electron transport chain. This force is used by ATP synthase to produce ATP.

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Enzymes and ATP Synthesis

ATP synthase is the key enzyme that utilizes the proton motive force to synthesize ATP from ADP and inorganic phosphate.

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Inhibitors of Electron Flow and ATP Synthesis

Various substances can inhibit electron transport or ATP synthesis at different steps. Examples include cyanide, carbon monoxide, and oligomycin.

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Uncoupling Electron Flow and ATP Production

Uncouplers (e.g., DNP) disrupt the coupling between electron transport and ATP synthesis, allowing protons to leak across the membrane, dissipating the gradient and decreasing ATP production.

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Material Transfer In/Out of Mitochondria

Specialized transport systems regulate the movement of molecules, such as pyruvate, fatty acids, and ADP, across the mitochondrial membranes.

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Regulation of Oxidative Phosphorylation

Oxidative phosphorylation is tightly regulated by factors like ATP/ADP ratio, NADH/NAD+ ratio, and oxygen availability.

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Study Notes

Oxidative Phosphorylation Overview

  • Oxidative phosphorylation is a metabolic process that uses energy from NADH and FADH₂ to produce ATP.
  • Carbohydrates, lipids, and amino acids are the primary reduced fuels for the cell.
  • Electrons from reduced fuel molecules are transferred to cofactors NADH or FADH₂.

Chemiosmotic Theory

  • Energy needed to phosphorylate ADP is provided by the flow of protons down the electrochemical gradient.
  • ∆G is related to ΔE = E₀ (e⁻ acceptor) – E₀ (e⁻ donor)
  • Electrons are transferred from lower (more negative) to higher (more positive) reduction potential.
  • Electrons released from redox processes, during electron transport transfer, power proton pumping against the electrochemical gradient.

Chemiosmotic Energy Coupling

  • The proton gradient, necessary for ATP synthesis, is stably established across a membrane, impermeable to ions.
  • Membranes in mitochondria
  • inner membrane
  • thylakoid membrane in chloroplasts
  • plasma membrane in bacteria
  • Proteins in the membrane couple 'downhill' flow of electrons with 'uphill' flow of protons across the membrane
  • Another protein within the membrane couples the 'downhill' flow of protons to the phosphorylation of ADP.

Electron Carriers in the Electron Transport Chain

  • Complexes in the electron transport chain contain multiple redox centers: flavin mononucleotide (FMN), and flavin adenine dinucleotide (FAD), cytochromes (a,b,c), and iron-sulfur clusters.
  • Electron transfer order depends on reduction potential.
  • These carriers have varying reduction potential (E'). Higher E' means greater tendency to accept electrons.

Coenzymes (FAD/FMN, NAD+/NADH, and FAD/FADH₂)

  • Coenzymes associated with dehydrogenases transfer hydride ions (H⁻), consisting of one proton and two electrons.
  • NAD(P)+/NAD(P)H, FMN/FMNH2, and FAD/FADH₂ are important electron carriers.
  • FAD/FMN transfer hydrogen atoms (one proton and one electron)

Coenzyme Q (Ubiquinone)

  • Lipid-soluble quinone, isoprenoid compound; readily accepts electrons from different redox-active compounds.
  • Accepts two electrons; picks up two protons to become ubiquinol.
  • Ubiquinol can diffuse freely in the membrane, carrying electrons with protons.
  • Coenzyme Q transports electrons from complexes I and II to Complex III.

Cytochromes (a, b, and c)

  • One-electron carriers based on Fe³⁺/Fe²⁺ redox systems.
  • Cytochromes a, b, and c, differ by ring additions and substitutions, which affect their redox properties.

Iron-Sulfur Proteins

  • One-electron carriers based on Fe³⁺/Fe²⁺ redox system.
  • Iron ions coordinated by cysteine residues in the protein.
  • Iron-sulfur clusters contain equal numbers of iron and sulfur atoms.

Chemiosmotic Model for ATP Synthesis

  • Electron transport through complexes I-IV establishes a proton-motive force (PMF).
  • The energy of PMF drives ATP synthesis via ATP synthase.
  • Includes the flow of electrons creates a concentration gradient of protons established across the membrane.

Mitochondrial ATP Synthase Complex

  • Consists of two functional subunits (Fo and F₁)
  • Fo is an integral membrane complex that transports protons from the intermembrane space to the matrix.
  • F₁ is a soluble complex in the matrix that hydrolyzes ATP.
  • Dimers, can exist in 3 different conformations (open, loose and tight).

Synthesis of ATP in ATP Synthase

  • Translocation of 3 protons fuels synthesis of one ATP molecule
  • Electrochemical energy generated through proton concentration gradients drives ATP synthesis.

Inhibitors and Uncouplers

  • Inhibitors block electron transport (e.g., cyanide, antimycin A).
  • Inhibitors block ATP synthase (e.g., oligomycin, venturicidin).
  • Uncouplers allow respiration to continue without ATP synthesis (e.g., dinitrophenol, valinomycin).
  • Uncouplers bypass H⁺ flow through the ATPase.

Mitochondrial Transport of Species

  • Translocation of a fourth proton per ATP is required.
  • This allows cotransport of substrates into and products out of the matrix.
  • Adenine nucleotide translocase and phosphate translocase are important transport proteins in the inner mitochondrial membrane.

Malate-Aspartate Shuttle

  • Transports reducing equivalents (NADH) from the cytosol into the mitochondrial matrix.
  • This shuttle is important in liver, kidneys, and heart.

Glycerol-3-Phosphate Shuttle

  • An alternative method used by skeletal muscle and brain tissues to transport reducing equivalents.
  • Transfers electrons through FADH₂, reducing NADH production efficiency by one ATP generated per NADH molecule.

Oxidation of Glucose

  • Oxidation of Glucose yields a total of 38 ATP molecules with the Malate Shuttle. With Glycerol Phosphate Shuttle the yield is 36 ATP.

Regulation of Oxidative Phosphorylation

  • Primarily regulated by substrate availability (NADH and ADP/Pi).
  • The rate of O₂ consumption and ATP synthesis is regulated by the intracellular concentration of ADP.
  • High ATP levels inhibit oxidative phosphorylation.

Mitochondria and Apoptosis

  • Mitochondrial membrane integrity loss during apoptosis (programmed cell death) releases cytochrome c that activates caspase proteases.

Mitochondrial Genetics

  • Mitochondrial DNA (mtDNA) is circular and carries 37 genes.
  • mtDNA encodes rRNA, tRNA molecules, and enzymes critical to oxidative phosphorylation.
  • Mitochondria have their own ribosomes but rely on nuclear DNA for most proteins.
  • mtDNA inheritance is maternal.
  • Mutations in mitochondrial DNA can produce various diseases.

Mitochondrial Mutations and Diabetes

  • Defects in oxidative phosphorylation can reduce ATP production.
  • This causes impaired insulin release from pancreatic beta cells which leads to a rare form of diabetes.

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Oxidative Phosphorylation - Chapter 19 PDF

Description

This quiz covers the key concepts of oxidative phosphorylation, including the role of NADH, FADH₂, and the chemiosmotic theory. Understand how energy is harnessed to synthesize ATP through the flow of protons and electron transfer. Test your knowledge on the metabolic processes underlying cellular respiration.

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