Page 1: Introduction to Electron Transport

Key Terms and Molecules

• Mitochondria: Organelles that perform electron transport and ATP synthesis.

• Acetyl-CoA: A key metabolite in energy production.

• NADH: Reduced form of nicotinamide adenine dinucleotide, important in electron transport.

• FADH2: Another key player in the electron transport chain.

• Complexes I-IV: Protein complexes in the electron transport chain.

• Cytochrome c: An important mobile electron carrier in mitochondria.

Page 2: Structure of Mitochondria

Membrane Composition

• Outer Membrane:

  • Permeable to small ions and molecules due to mitochondrial porin channels.

• Inner Membrane:

  • Folded into cristae, creating surface area for reactions.

  • Imprenable to nucleotides and protons, containing cardiolipin to support its structure.

Functionality

• Site of electron transport and ATP synthesis, indicating the significance of mitochondrial membranes in cellular respiration.

Page 3: Oxidative Phosphorylation

Process Overview

• Location in Eukaryotes: Occurs in mitochondria; essential for energy production.

• Electron Flow: Electrons from NADH and FADH2 to O2, catalyzed through the electron transport chain.

• Proton Gradient: Essential for ATP synthesis; generated through oxidative phosphorylation.

Page 4: Measuring Electron-Transfer Potential

Redox Potential

• Definition: Measures ability of X- to donate electrons to H+.

• Directionality of Reaction: X- + H+ → X + ½ H2 indicates electron flow direction.

• Measurement: Assessed by potential difference via voltmeter.

Page 5: Reduction Potential

Key Concepts

• E0′: Indicates tendency for species to acquire electrons.

• Strong Reducing Agents: Negative E0′, capable of donating electrons.

• Strong Oxidizing Agents: Positive E0′, able to accept electrons.

• Energy Dynamics: Related to the free-energy change.

  • ΔGo′ = -nFΔE0′ (n = number of electrons, F = Faraday constant).

Page 6: Structure of the Electron Transport Chain

Components

• Comprised of four protein complexes that facilitate electron transfer from NADH and FADH2 through various electron carriers:

  • FMN: Flavin mononucleotide.

  • Iron-Sulfur Proteins: Essential for electron transport.

  • Cytochromes: Containing iron for electron transfer.

  • Coenzyme Q: A mobile carrier that accepts and transports electrons.

Page 7: Complex I Functionality

Mechanism

• Electron Donation: Electrons are donated from NADH to FMN carrier in Complex I.

• Oxidation Process: NADH is oxidized to NAD+ while facilitating electron transport.

• Single Electron Transfer: Transfers electrons to carriers that process one electron at a time.

Page 8: Coenzyme Q Role

Functionality

• Electron Transport: Transporting electrons between Complexes I and II to Complex III.

• Chemical Properties: Upon accepting 2 electrons, converts to ubiquinol by picking up 2 protons.

• Mobility: Freely diffuses in the membrane.

Page 9: Iron-Sulfur Clusters

Role in Electron Transfer

• Single Electron Carriers: Utilized at several points in the electron transport chain.

• Standard Reduction Potential: Varies due to micro-environment and interactions with associated proteins.

Page 10: Cytochromes Structure

Characteristics

• Nature of Cytochromes: Composed of iron-coordinating porphyrin rings, allowing them to act as one electron carriers between complexes III and IV.

Page 11: Flow of Electrons

Energy Gradient Dynamics

• Catalyzed Flow: From NADH to O2 through four protein complexes.

• Proton Translocation: Involved in three complexes (I, III, and IV) while Complex II does not pump protons.

• Succinate-Q Reductase: Delivers electrons from FADH2 to Complex III.

Page 12: Complex I Mechanism

Actions of Complex I

• NADH Conversion: Converts NADH to NAD+ and Q to QH2.

• Proton Pumping: Pumps out four protons during this reaction.

• Inhibition: Poisons like Rotenone inhibit Complex I functionality.

Page 13: Complex II Mechanism

Electron Transfer

• Electrons from Succinate: FAD reduces succinate to transfer electrons through iron-sulfur centers to ubiquinone.

• Proton Pumping: Complex II does not pump protons unlike Complex I.

Page 14: Q Pool Dynamics

Functionality

• Q Pool Reference: Represents reduced and oxidized forms in the inner membrane.

• Q Cycle Mechanism: Enables efficient transfer of electrons along with proton translocation.

Page 15: Complex III Mechanism

QH2 Actions

• Electron Transfer to Cyt c: Utilizes electrons from QH2 to reduce cytochrome c while pumping additional protons to the intermembrane space.

• Inhibition Check: Inhibition by antimycin.

Page 16: The Q Cycle Steps

Mechanism Breakdown

• Step 1: QH2 binds and transfers electrons leading to cytochrome C reduction, pumping protons.

• Step 2: Another QH2 binds, repeating electron transfer and proton pumping.

• Outcome: Production of cytochrome C and proton movement.

Page 17: Q Cycle Overview

Functionality Summary

• Electron Transfer Mechanics: Reduces proton accumulation through efficient transfer between carriers.

Page 18: Role of Cytochrome C

Function in Electron Transport

• Movement Space: Cytochrome C as a mobile carrier moving between complexes III and IV.

• Electron Carriage: Transporting one electron each time to the terminal complex.

Page 19: Function of Complex IV

Cytochrome C Oxidase Activity

• Final Electron Acceptance: Reduces O2 to water.

• Proton Removal: Eight protons are involved in this process with four pumped outward.

Page 20: Molecular Reduction Process

Key Mechanism

• Peroxide Bridge Formation: Involved when O2 is reduced, producing significant intermediate species.

Page 21: Summary of Electron Flow

Key Points

• Proton Pumping Sites: Complexes I, III, IV are primarily responsible.

Page 22: Environmental Concerns

Understanding "Dead Zones"

• Impact of Respiration: Excessive respiration can deplete O2 levels leading to dead zones.

Page 23: Secondary Electron Fate

Two Possible Outcomes

• O2 Reduction: Can form superoxide ions or peroxide under imperfect conditions, explaining ROS generation.

Page 24: Reactive Oxygen Species (ROS)

Roles in Biology

• Dual Nature of ROS: Significantly impacts biological macromolecules positively and negatively.

Page 25: Reactive Species Dynamics

Generating and Handling Superoxide

• Various Reactions: Details of reactions involving detoxifying mechanisms such as SOD and Catalase.

Page 26: Free Radical Injury Conditions

Notable Pathological Conditions

• Link to Free Radicals: Various conditions are potentially due to oxidative stress and free-radical injury. (e.g., Atherogenesis, Parkinson’s disease, etc.)