Bioc384-M11.T02-Chemiosmosis-Miesfeld

The Chemiosmotic Theory

  • Established by Peter Mitchell in the early 1960s at the Glynn Research Institute.

  • The institute started with less than 20 staff and was a private institution for almost 30 years.

Key Concepts of the Chemiosmotic Theory

  • States that energy from redox reactions is converted into a proton gradient.

  • This process couples electron transfer to membrane-bound proton pumps.

  • Proton circuit consists of:

    • Chemical gradient (DpH)

    • Membrane potential (ΔΨ)

  • Proton-motive force is used for ATP synthesis through protein conformational changes.

  • Proof came from experiments using artificial membranes with heterologous proteins that created a proton gradient and synthesized ATP.

Oxidative Phosphorylation

  • Composed of Electron Transport System (ETS) and ATP synthesis by ATP Synthase complex.

  • Processes catabolize carbon-based fuels to reduce O2, generating H2O and ATP.

Mechanism of Oxidative Phosphorylation

  • NADH and FADH2 are oxidized in the mitochondrial matrix.

  • Links redox energy to ATP synthesis.

  • Involves the outward pumping of H+ through ETS complexes (I, III, IV) in mitochondria.

  • H+ flows down the proton gradient through ATP synthase complex due to a chemical and electrical differential.

Energy Conversion Requirements

  • Mitochondrion and chloroplast are primary sites.

  • Proton circuits exist across membranes:

    • Inner mitochondrial membrane

    • Thylakoid membranes in chloroplasts

  • Proton gradient essential for ATP production by ATP synthase.

  • Flow of protons creates electrical current; the ETS acts as a battery, the gradient as a capacitor, and the ATP synthase as a resistor.

Structure of Mitochondria

  • Contains inner and outer membranes.

  • The inner membrane has a large surface area crucial for ATP production.

  • Difference in mitochondrial content is reflected in the muscle types of animals (e.g. turkey).

Overview of the Chemiosmotic Theory

  • Involves the electron transport system (I–IV), cytochrome c, and ATP synthase.

Peter Mitchell and the Chemiosmotic Hypothesis

  • The concept of electrochemical gradients powering ATP generation was initially controversial.

  • Peter Mitchell proposed this in 1961 and won the Nobel Prize in Chemistry in 1978.

Pathway Questions

  1. What does oxidative phosphorylation accomplish?

    • Generates ATP from oxidation of metabolic fuels, accounting for 28 of 32 ATP (88%) from glucose.

    • UCP1 in brown adipose tissue allows heat production through electron transport system short-circuiting.

  2. Net reaction of NADH oxidation?

    • 2 NADH + 2 H+ + 5 ADP + 5 Pi + O2 → 2 NAD+ + 5 ATP + 2 H2O

  3. Key enzymes in the pathway?

    • ATP synthase complex

    • NADH dehydrogenase

    • Ubiquinone-cytochrome c oxidoreductase

    • Cytochrome c oxidase

  4. Real life examples?

    • Cyanide poisoning linked to inhibited electron transport leading to cell death.

Evidence Supporting Mitchell's Theory

  • Light-activated ATP synthesis in reconstituted vesicles demonstrated the validity of the chemiosmotic hypothesis.

  • These vesicles had artificial membranes, bacteriorhodopsin, and ATP synthase from bovine mitochondria.