Week 7-1 Respiration - Electron Transport Systems

Chapter Overview

  • Topics Covered:

    • Electron transport systems (ETS)

    • Respiratory ETS

    • E. coli ETS

    • Mitochondrial ETS

    • Proton motive force (PMF)

    • ATP synthase

    • Anaerobic respiration

Complete Oxidation of Glucose

  • Process Overview:

    • 16 electrons are carried through the process:

      • 6 NADH + 6H+ from glycolysis

      • 2 FADH2

    • Key steps involved:

      • Glycolysis: 2 Pyruvate (3C), yielding 2 NADH, and inputting 2 ATP.

      • Transition: Conversion of 2 pyruvates to 2 acetyl-CoA, yielding 2 NADH.

      • TCA Cycle: From 2 acetyl-CoA, results in 6 NADH, 2 FADH2, 2 ATP, and 4 CO2.

      • Total production from one glucose molecule results in theoretical maximum of 36 ATP.

Role of NADH and FADH2 in Respiration

  • Usage:

    • Electrons from NADH and FADH2 are donated to bacterial ETS to generate ATP via oxidative phosphorylation.

Electron Acceptors

  • Types:

    • Aerobic Respiration: Utilizes molecular oxygen (O2) as a terminal electron acceptor (TEA) in the electron transport chain.

    • Anaerobic Respiration: Unique to prokaryotes, utilizing alternative electron acceptors such as metals and oxidized nitrogen.

Proton Motive Force (PMF)

  • Definition:

    • Generated by transfer of H+ through proton pumps, driving ATP conversion through ATP synthase.

  • Chemiosmotic Theory:

    • Proposed by Peter Mitchell, earning him the Nobel Prize in 1978.

ATP Synthase Mechanism

  • Function:

    • Harvests energy from proton motive force to synthesize ATP.

    • 10 protons pumped out per NADH yields 3 ATP; 6 protons per FADH2 yields 2 ATP.

Mitochondrial vs E. coli ETS

  • Differences:

    • Mitochondrial ETS has an intermediate ubiquinol:cytochrome c oxidoreductase complex for electron transfer.

    • Pumps 12 H+ per NADH compared to E. coli's 8-10 H+.

Summary of Anaerobic Respiration

  • Alternative Acceptors:

    • Some prokaryotes reduce nitrate (NO3– to NO2–) and sulfate (SO42– to SO32–) as alternative electron acceptors in environments where oxygen is limited.

Key Components of Electron Transport Systems

  • Functional Components:

    • Substrate dehydrogenase

    • Mobile electron carrier

    • Terminal oxidase

  • Electron Carriers:

    • Contain metal ions and/or conjugated ring structures, facilitating electron transfer.

  • ATP Production:

    • F1Fo ATP synthase produces ATP, driven by the flow of protons.

Conclusion

  • Electron transport systems are crucial for cellular respiration, facilitating energy production and driving metabolic processes in both aerobic and anaerobic organisms.