Electron Transport Chain and Oxidative Phosphorylation

• Stages of Catabolism:

  1. Acetyl group formation
  2. Citric Acid Cycle (TCA/Krebs)
  3. ETC and OP
• NAD+ - Nicotinamide adenine dinucleotide

  NADP+ - Nicotinamide adenine dinucleotide phosphate

  Enzyme use for REDOX - dehydrogenase
• FAD+ - Flavin adenine dinucleotide

  FMN - Flavin mononucleotide
• Ubiquinone - Coenzyme Q, CoQ
• Cytochromes - has Fe
• Coenzyme A - CoA
• Fe-S Proteins - can have single to 4 iron and S
• ETC/Respiratory Chain - A series of rxns in w/c e- and H+ are passed from NADH and FADH2 to intermediate carriers and ultimately react with molecular O2 to produce H2O.
• One O2 will need 4 electrons to produce 2 water
• Oxidative Phosphorylation - Conversion of e- transfer potential to phosphate transfer potential.

  Oxidation involves the tranformation of NADH and FADH2 to NAD+ and FAD

  Phosphorylation involves transformation of ADP to ATP.
• Oxidative Phosphorylation - major source of ATP in anaerobic organisms.
• NADH yields 2.5 ATPs
• FADH2 yields 1.5 ATPs
• Location of ETC: Mitochondria
• Complexes in the Inner Membrane

  ETC:

  Complex I - NADH coenzyme Q oxidoreductase (NADH dehydrogenase)

  Complex II - Succinate-coenzyme Q oxidoreductase

  Complex III - coenzyme Q-cytochrome c oxidoreductase/reductase

  Complex IV: Cytochrome c oxidoreductase/oxidase

  OP:

  Complex V - ATP synthase

  Mobile Carriers:

  Ubiquinone and Cytochrome C
• In Complex I:

  1. e- from NADH enter at Complex I
  2. 2H atoms via reduction of FMN
  3. e- transfer to Fe3+
  4. Hydrogens become proton and move back to matrix
  5. e- transfer to Ubiquinone (UQH2)
  6. e- transfer to Fe again
  7. 2 H+ releases to intermembrane space
  8. e-transfer to Fe3+ and UQ again
  9. 2nd UQ is mobile
• Complex II:

  1. 2e- from TCA cycle (Succinate to Fumerate)
  2. e- trans to FAD
  3. e- trans to Fe-S
  4. e-trans to mobile UQ
  5. Not enough active trans of H
• CIII:

  1. e- from CI or CII from UQ
  2. 2 e- are moved one at a time through a pathway involving Fe-S and cytochromes c1, bL & bH
  3. As es pass through Fe-S and cytochromes, 2H+ are pumped across the membrane.
  4. Electrons are passed from CIII one at a time to cytochrome c, a water-soluble mobile ecarrier.
• CIV:

  1. e- for reduction of O2 to H2O
• Electrons move through ETC by the overall NEGATIVE Delta G as they move through coenzymes & metal donors and acceptors.
• Electron transport & ATP synthesis are coupled by a proton gradient across the inner mitochondrial membrane.
• As e- are transported through the ETC, H+ are pumped out of the matrix, thus increasing the [H+] in the intermembrane space.
• Gradient is relieved by passage of H+ through Complex V (ATP synthase). The process is coupled to ATP synthesis from ADP + Pi.
• Fo unit acts as proton channel or entry point of H+ back into the matrix.

  F1 contains the catalytic site for ATP synthesis.
• Rotenone, Amytal, Piericidine - competes w/ UQ because they similar structures.
• ROTENONE - blocks NADH dH to Q, but ATP can still be produced from Complex II (through FADH2)
• CN- and N3- react with Fe3+ form of heme in cyt a3

  CO – inhibits the Fe2+ form
• Uncouplers/Pyrogen - allow e- transport in mitochondrion BUT prevents phosphorylation of ADP to ATP by uncoupling the essential linkage between ETC and ATPase.
• Thermogenin

  Uncoupling protein in brown tissue mitochondrion

  Forms a pathway for H+ from cytosol to the matrix

  Generates heat by “short circuiting” the mitochondrion proton battery
• Ionophores

  Also prevents Ox. Phos.

  Lipid-soluble compounds that carry specific

  ions through the membrane

  promote transfer of CATIONS rather than H+ from the membrane

  Valinomycin and Gramicidin
• Oligomycin & dicycloheylcarbodiimide

  (DCCD)

  Prevent the influx of H+ through ATPase.