Mitochondrial Function and Evolution
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Questions and Answers

What is the primary function of oxidative phosphorylation in aerobic organisms?

  • Conversion of energy to heat
  • Storage of carbohydrates
  • Decomposing nucleic acids
  • Synthesis of ATP (correct)

Oxidative phosphorylation occurs only in prokaryotic cells.

False (B)

What major evolutionary event led to the origin of mitochondria?

Endosymbiotic relationship with bacteria

The final electron acceptor in the mitochondrial respiratory chain is __________.

<p>molecular oxygen</p> Signup and view all the answers

Which process is NOT associated with mitochondrial function?

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

Match the mitochondrial functions to their descriptions:

<p>ATP Synthesis = Production of cellular energy Thermogenesis = Heat production Apoptosis = Programmed cell death Fatty acid oxidation = Breakdown of fats for energy</p> Signup and view all the answers

The appearance of oxygen in the atmosphere around 2.3 billion years ago was crucial for the evolution of more complex life forms.

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

In eukaryotes, where does oxidative phosphorylation take place?

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

What is the typical size range of mitochondria?

<p>1 to 10 μm (B)</p> Signup and view all the answers

Mitochondria contain enzymes for glycolysis.

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

What types of fuels do the pathways in the mitochondrial matrix oxidize?

<p>Pyruvate, fatty acids, and amino acids</p> Signup and view all the answers

The __________ is a selectively permeable membrane that segregates metabolic pathways.

<p>inner mitochondrial membrane</p> Signup and view all the answers

What percentage of proteins in mammalian mitochondria are currently enigmatic in function?

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

Match the following tissues with their mitochondrial demand:

<p>Brain = High demand for aerobic metabolism Skeletal Muscle = High demand for aerobic metabolism Skin = Low demand for aerobic metabolism Liver = High demand for aerobic metabolism</p> Signup and view all the answers

What cellular process allows mitochondria to divide?

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

Mitochondria can fuse under certain circumstances.

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

What function is associated with Complex II in the citric acid cycle?

<p>Conversion of succinate to fumarate (D)</p> Signup and view all the answers

Heme b in Complex II is in the direct path of electron transfer.

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

What is the primary consequence of mutations in Complex II subunits near heme b?

<p>Increased production of reactive oxygen species (ROS)</p> Signup and view all the answers

The binding site for succinate is located in subunit __ of Complex II.

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

Match the following components of Complex II with their functions:

<p>Heme b = Reduces electron leakage FAD = Initial electron acceptor Iron-sulfur centers = Transfer electrons to ubiquinone Ubiquinone = Final electron acceptor in Complex II</p> Signup and view all the answers

Individuals with hereditary paraganglioma typically have mutations near which site in Complex II?

<p>Ubiquinone-binding site (B), Heme b-binding site (C)</p> Signup and view all the answers

Complex II solely impacts the citric acid cycle without any relation to mitochondrial electron transfer.

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

What are the reactive oxygen species (ROS) produced when electrons leak from the system?

<p>Hydrogen peroxide (H2O2) and superoxide radical (·O2−)</p> Signup and view all the answers

What is Complex III also known as?

<p>Ubiquinone:cytochrome c oxidoreductase (A)</p> Signup and view all the answers

Complex III consists of a single monomer.

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

Name one of the proteins central to the action of Complex III.

<p>Cytochrome b, cytochrome c, or the Rieske iron-sulfur protein</p> Signup and view all the answers

The functional core of each monomer of Complex III consists of three subunits: cytochrome b, the Rieske iron-sulfur protein, and ___ .

<p>cytochrome c</p> Signup and view all the answers

Which sites on Complex III correspond to its ubiquinone binding sites?

<p>Site Q and Site N (D)</p> Signup and view all the answers

Antimycin A binds to the site Q on Complex III, blocking electron flow from cytochrome b to cytochrome c1.

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

What process do the actions of Complex III couple with?

<p>Proton transport</p> Signup and view all the answers

Match the following subunits/proteins with their respective characteristics:

<p>Cytochrome b = Contains two hemes Rieske iron-sulfur protein = Contains 2Fe-2S centers Cytochrome c = Interacts with cytochrome c in the intermembrane space Ubiquinone = Shuttles electrons and protons across the membrane</p> Signup and view all the answers

What is the primary role of glycerol 3-phosphate dehydrogenase in the respiratory chain?

<p>Shuttling reducing equivalents from NADH to the mitochondrial matrix (D)</p> Signup and view all the answers

Ubiquinone is reduced to QH in the inner mitochondrial membrane by glycerol 3-phosphate dehydrogenase.

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

What do the electron carriers cytochrome c and ubiquinone do in the context of supercomplexes?

<p>They facilitate electron transfers and limit the production of reactive oxygen species.</p> Signup and view all the answers

In β oxidation of fatty acyl–CoA, electrons are first transferred to the ___ of the dehydrogenase.

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

Match the following components with their respective roles in the respiratory chain:

<p>Cytochrome c = Facilitates electron transfer Ubiquinone = Electron carrier Acyl-CoA dehydrogenase = Catalyzes β oxidation Dihydroorotate dehydrogenase = Donates electrons to ubiquinone</p> Signup and view all the answers

Which of the following statements is accurate regarding electron transfer pathways?

<p>Multiple electron-transfer reactions can reduce ubiquinone. (A)</p> Signup and view all the answers

The reduced ubiquinone (QH) passes its electrons through Complex I.

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

Name the two electron carriers mentioned in the respiratory chain that can diffuse between supercomplexes.

<p>Cytochrome c and ubiquinone</p> Signup and view all the answers

What happens to the vesicles when F is depleted?

<p>They cannot produce a proton gradient. (C)</p> Signup and view all the answers

Is ATP hydrolysis the same as ATP synthesis?

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

What was the original name given to the isolated F that catalyzes ATP hydrolysis?

<p>F ATPase</p> Signup and view all the answers

The terminal __________ bond in ATP is cleaved and re-formed repeatedly on the enzyme surface.

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

What does isotopic analysis of ATP synthesis reveal about the free-energy change?

<p>It is close to zero. (B)</p> Signup and view all the answers

Match each component to its description:

<p>F = Catalyzes ATP hydrolysis NADH = Electron donor in respiration ADP = Produces ATP when converted Pi = Inorganic phosphate involved in ATP synthesis</p> Signup and view all the answers

Purified F can restore ATP synthesis capability to depleted vesicles.

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

What does the presence of multiple 18O atoms in P released during ATP hydrolysis indicate?

<p>The terminal pyrophosphate bond is cleaved and re-formed multiple times.</p> Signup and view all the answers

Flashcards

Oxidative Phosphorylation

The final stage of cellular respiration where energy from oxidation is used to create ATP.

ATP Synthesis

The process of creating ATP, the main energy currency of cells.

Mitochondria

Organelles where oxidative phosphorylation occurs in eukaryotes; central role in aerobic metabolism.

Aerobic Organisms

Organisms that use oxygen in their metabolic processes.

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Cellular Respiration

Series of metabolic reactions that break down food to release energy (ATP).

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Electron Transport Chain

A series of protein complexes that transfer electrons to a final electron acceptor (oxygen).

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Endosymbiotic Relationship

A close, long-term biological relationship between different biological species.

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Eukaryotes

Organisms with a nucleus and membrane-bound organelles.

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Mitochondria Size

Mitochondria, the powerhouses of cells, are typically 1-10 µm in length, similar in size to bacteria.

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Mitochondrial Matrix

The inner compartment of mitochondria, containing enzymes for fuel oxidation, excluding glycolysis.

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Inner Mitochondrial Membrane

A selectively permeable membrane separating the mitochondrial matrix from the cytosol, controlling the movement of molecules in and out of the matrix.

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Fuel Oxidation Pathways

Processes enclosed in the mitochondrial matrix, like the citric acid cycle, β-oxidation, and amino acid oxidation, that break down fuels for energy.

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Mitochondrial Transporters

Specialized proteins that move essential molecules like pyruvate, fatty acids and amino acids into the mitochondrial matrix.

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ATP/ADP Transport

Mitochondria efficiently move ATP out and ADP/Pi in to support cellular energy needs.

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Mitochondrial Protein Complexity

Mammalian mitochondria contain many proteins, about 1200, with many functions still unknown.

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Mitochondrial Shape Variability

Mitochondria vary considerably in size and shape, not just bean-shaped, especially when observed in 3D or in living cells.

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Complex II Function

Complex II, also known as succinate dehydrogenase, is a part of the citric acid cycle that coordinates the cycle with electron transfer in mitochondria.

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Complex II Structure

Complex II has transmembrane subunits (C and D) and matrix subunits (A and B). It contains FAD, Fe-S centers, ubiquinone, and heme b.

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Electron Transfer in Complex II

Electrons travel from succinate to FAD, through Fe-S centers, and finally to ubiquinone.

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Heme b in Complex II

Heme b in Complex II is not directly involved in main electron transfer, but it stops stray electrons from forming harmful molecules (ROS).

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Reactive Oxygen Species (ROS)

ROS are harmful byproducts like hydrogen peroxide and superoxide, produced when electrons 'leak' to oxygen directly.

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Hereditary Paraganglioma

A disease caused by mutations in Complex II subunits near heme b or ubiquinone binding sites.

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Mutations in Succinate Binding Region

Mutations in the succinate-binding region of Complex II can lead to central nervous system degeneration and adrenal tumors.

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Complex III Function

Complex III takes electrons from reduced ubiquinone (ubiquinol) and passes them to cytochrome c.

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Complex III

A protein complex in the electron transport chain, transferring electrons from ubiquinol to cytochrome c and pumping protons across the mitochondrial membrane.

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Ubiquinol

The reduced form of ubiquinone, a mobile electron carrier in the Electron transport chain. It carries electrons from Complex I and II to Complex III.

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Cytochrome c

A small, mobile protein that carries electrons from Complex III to Complex IV in the electron transport chain.

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Rieske Iron-Sulfur Protein

A protein in Complex III that contains a Fe-S cluster and plays a crucial role in electron transfer.

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Vectorial Transport

The directed movement of molecules across a membrane, in a specific direction. In Complex III, protons are transported from the mitochondrial matrix to the intermembrane space.

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Q & Q Sites

Two distinct binding sites for ubiquinone on Complex III. Site Q is on the matrix side, while site Q is on the intermembrane space side.

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Antimycin A

A drug that inhibits Complex III by specifically blocking electron flow from cytochrome b to cytochrome c at the Q site.

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How does Complex III contribute to ATP synthesis?

Complex III couples electron transport with proton pumping, creating a proton gradient across the mitochondrial membrane. This gradient is used by ATP synthase to generate ATP.

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Respirasome

A complex of respiratory chain proteins (Complexes I, III, and IV) that work together to transfer electrons and produce ATP. It's like a team of athletes, each performing a specific role in the process.

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Electron Carriers

Molecules that transport electrons during electron transfer reactions in the respiratory chain. They act like shuttles, carrying electrons from one protein to another.

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Ubiquinone (Q)

A mobile electron carrier in the respiratory chain. It accepts electrons from various sources and shuttles them to Complex III.

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β oxidation of Fatty Acyl-CoA

A process that breaks down fatty acids into smaller units, releasing energy that can be used for ATP production. It's like splitting a long chain into smaller pieces to release energy.

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Glycerol 3-Phosphate Dehydrogenase

An enzyme that converts glycerol 3-phosphate to dihydroxyacetone phosphate, releasing electrons that are then used for ATP production. It acts like a converter, transforming energy from one form to another.

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Dihydroorotate Dehydrogenase

An enzyme involved in pyrimidine synthesis that donates electrons to the respiratory chain. It's like a helper enzyme contributing to the overall process of energy production.

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QH2

The reduced form of ubiquinone (Q), carrying electrons. Think of it like a filled bag of electrons.

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Proton Gradient

Difference in proton concentration across a membrane. It acts as a driving force for ATP synthesis.

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ATP Hydrolysis

The breakdown of ATP into ADP and inorganic phosphate (Pi) by F1.

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F1-depleted Vesicles

Mitochondrial vesicles where the F1 portion of ATP synthase has been removed.

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ATP Synthesis Reversal

When F1 catalyzes ATP hydrolysis, it acts in the reverse direction of ATP synthesis.

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Isotope Exchange Experiments

Experiments using radioactively labeled atoms to study enzyme mechanisms. These experiments revealed the dynamic nature of ATP synthesis.

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ATP Cleavage and Re-formation

The terminal phosphate bond in ATP is repeatedly broken and reformed on the surface of F1 before Pi is released.

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Study Notes

Oxidative Phosphorylation

  • Oxidative phosphorylation is the final stage of aerobic catabolism in organisms
  • It's the culmination of energy-yielding metabolic processes
  • All oxidative steps in the degradation of carbohydrates, fats, and amino acids converge at this stage of cellular respiration
  • The energy of oxidation drives the synthesis of ATP
  • This process accounts for most ATP synthesis in nonphotosynthetic organisms
  • In eukaryotes, it occurs in mitochondria, involving huge protein complexes embedded in the mitochondrial membranes
  • The pathway to ATP synthesis occurs within mitochondria

Mitochondrial Respiratory Chain

  • The respiratory chain is a series of membrane-bound electron carriers
  • Electrons flow from electron donors (oxidizable substrates) to a final electron acceptor (usually oxygen)
  • This flow generates an electrochemical potential across the membrane, which is used to drive ATP synthesis
  • The chain consists of protein complexes, each performing specific electron-transfer reactions

Principles of Oxidative Phosphorylation

  • Principle 1: Mitochondria play a central role in aerobic metabolism, acting as the site of the citric acid cycle, fatty acid β-oxidation, and amino acid oxidation pathways
  • Principle 2: Mitochondria trace their evolutionary origin to bacteria, evident in their structure and function
  • Principle 3: Electrons flow via a chain of membrane-bound carriers to the final electron acceptor, oxygen (O2)
  • Principle 4: Free energy from exergonic electron flow is used to transport protons across a membrane
  • Principle 5: Proton movement back through specific channels provides energy for ATP synthesis.

Mitochondria: Components and Function

  • Outer membrane: readily permeable to small molecules and ions
  • Inner membrane: impermeable to most small molecules and ions, including protons (H+). Contains the crucial electron transfer chain components and ATP synthase
  • Cristae: foldings in the inner membrane, increasing surface area for electron transfer reactions
  • Matrix: fluid-filled space inside the inner membrane, containing enzymes of the citric acid cycle, fatty acid β-oxidation, and amino acid oxidation
  • Ribosomes: mitochondria's own ribosomes synthesize some proteins

Electron Carriers in the Respiratory Chain

  • Ubiquinone (Coenzyme Q): hydrophobic quinone, readily diffuses within the membrane, accepting single or double electrons
  • Cytochromes: proteins with heme prosthetic groups; absorb visible light, and participate in one-electron transfers
  • Iron-sulfur proteins: proteins containing iron-sulfur clusters; readily accept or donate single electrons.

Electron Carrier Complexes within the Respiratory Chain

  • Complex I (NADH dehydrogenase): Oxidizes NADH and transfers electrons to ubiquinone. Pumps protons across the inner mitochondrial membrane
  • Complex II (succinate dehydrogenase): Oxidizes succinate and transfers electrons to ubiquinone. Does not pump protons
  • Complex III (ubiquinone-cytochrome c oxidoreductase): Transfers electrons from ubiquinol (QH2) to cytochrome c. Pumps protons
  • Complex IV (cytochrome c oxidase): Transfers electrons from cytochrome c to oxygen (O2), reducing it to water (H2O). Pumps protons

The Q Cycle

  • The Q cycle is how Complex III accepts electrons from ubiquinol, moving electrons to cytochrome c and pumping protons across the inner membrane
  • Two molecules of ubiquinol are sequentially oxidized, releasing 4 protons
  • This process is central to using the energy from electrons to create a proton gradient

Complex IV (Cytochrome C Oxidase)

  • Complex IV is responsible for transferring electrons from cytochrome c to oxygen to produce water
  • It contains a binuclear center with copper atoms and a heme group, and this allows for efficient electron transfer and proton pumping
  • Involves the binding and reduction of oxygen to release water

Regulation of Oxidative Phosphorylation

  • The rate of oxidative phosphorylation is typically controlled by the availability of ADP and oxygen.
  • Other conditions, such as the ADP/ATP ratio or intracellular concentrations, can also affect the rate of the process
  • The cell regulates oxidative phosphorylation to ensure ATP production matches the rate of ATP consumption

Uncoupling Protein 1 (UCP1)

  • Brown adipose tissue (BAT) uses UCP-1 to uncouple mitochondrial respiration from ATP synthesis—producing heat instead of ATP from fuel oxidation

Mitochondrial P-450 Monooxygenases

  • Involved in steroid hormone biosynthesis.
  • Located in the inner mitochondrial membrane.

Mitochondrial DNA and Mutations

  • Mitochondria contain their own DNA (mtDNA) separate from nuclear DNA
  • mtDNA codes for some proteins needed for cellular respiration
  • Mutations in these are more pronounced with age due to the increased oxidative stress on the molecule
  • Mutations in mitochondrial genes may lead to several diseases, affecting different cell types varying in severity or severity of symptoms
  • Mitochondrial DNA mutations often affect the number and distribution of affected mitochondria, resulting in disease phenotypes that vary among individuals having the same mutation

Apoptosis

  • Apoptosis, or programmed cell death, is a normal process that involves mitochondrial dysfunction
  • This dysfunction leads to an increase in the permeability of the outer mitochondrial membrane, which allows Cytochrome c to leave. This process triggers a cascade of events leading to cell death

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Description

This quiz explores key concepts related to mitochondrial function and oxidative phosphorylation in aerobic organisms. It covers the evolutionary origins of mitochondria, their roles in energy production, and the significance of oxygen in the development of complex life forms. Test your understanding of these essential cellular processes.

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