ELECTRON TRANSPORT CHAIN
Dr. Gangadhar Chatterjee
05-3-2013
POINTS TO BE DISCUSSED
• MITOCHONDRIA
- Highly folded Inner mitochondrial
membrane
- ion and metabolite entry via transpor...
Energy can take many forms, including light and sound. The
mitochondria in eukaryotic cells facilitate energy transformati...
The Mitochondrion
• Mitochondria – a result of endosymbiotic event (
a free-living organism capable of oxidative
phosphory...
Ions and Metabolites Enter
Mitochondria via Transporters
• freely permeable only to O2, CO2, and H2O
• Cytosolic Reducing ...
A Translocator Exchanges ADP and ATP
• also called the adenine nucleotide translocase
• Inhibitor of the ATP–ADP transloca...
Phosphate Must Be Imported into the
Mitochondrion
phosphate carrier
Electroneutral Pi–H+ symport
driven by ΔpH
Formation of NADH and FADH2
Electron Transport Is an
Exergonic Process
• In mitochondria electrons pass through three
protein complexes.
• This allows the overall free energy change to
be broke...
Electron Carriers Operate in Sequence
Inhibitors Reveal the Workings of the
Electron-Transport Chain.
• Sequence of events elucidated largely through
the use of...
Standard Reduction Potentials of Some
Biochemically Important Half-Reactions
The mitochondrial electron-transport chain.
Complex I Accepts Electrons from NADH
• NADH–coenzyme Q oxidoreductase
• largest protein complex in the inner
mitochondria...
[2Fe–2S]

[4Fe–4S]
The oxidation states of FMN and coenzyme Q.
Complex II Contributes Electrons to
Coenzyme Q
• succinate–coenzyme Q oxidoreductase
• Complex II Contains a Linear Chain ...
Complex III Translocates Protons
via the Q Cycle
• coenzyme Q–cytochrome c oxidoreductase
• Contains - two b-type cytochro...
Electrons from Coenzyme Q Follow
Two Paths
• bifurcation of the flow
of electrons from
CoQH2 to cytochrome
c1 and to cytoc...
CoQH2 undergoes a two-cycle reoxidation
in which the semiquinone, Co Q. , is a stable
intermediate
• The net reaction is t...
Cytochrome c Is a Soluble Electron Carrier
• positively charged
residues constitute
binding sites for
complementary
negati...
Complex IV Reduces Oxygen to
Water
• Cytochrome-c oxidase

• four redox centers:
cytochrome a
cytochrome a3

a copper atom...
Electron Transport Generates a Proton Gradient
• Electron transport causes Complexes I, III, and IV
to transport protons a...
•

free energy change

• φ

Faraday constant

• ψ

membrane potential
CLINICAL ASPECT

• Fatal Infantile
Mitochondrial Myopathy
and renal dysfunction
involves severe diminution
or absence of m...
THANK YOU
Electron transport chain
Electron transport chain
Electron transport chain
Electron transport chain
Electron transport chain
Electron transport chain
Electron transport chain
Electron transport chain
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Electron transport chain

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Electron transport chain

  1. 1. ELECTRON TRANSPORT CHAIN Dr. Gangadhar Chatterjee 05-3-2013
  2. 2. POINTS TO BE DISCUSSED • MITOCHONDRIA - Highly folded Inner mitochondrial membrane - ion and metabolite entry via transporters • ELECTRON TRANSPORT - an exergonic process - carriers operate in sequence - complex-I to IV , cytochrome c
  3. 3. Energy can take many forms, including light and sound. The mitochondria in eukaryotic cells facilitate energy transformations involving chemical energy, mechanical energy , and the energy of a proton gradient during the process of ATP synthesis.
  4. 4. The Mitochondrion • Mitochondria – a result of endosymbiotic event ( a free-living organism capable of oxidative phosphorylation was engulfed by another cell ) • A highly folded, protein-rich inner membrane separates the mitochondrial matrix from the outer membrane. • Transport proteins are required to import reducing equivalents, ADP, and Pi into the mitochondria.
  5. 5. Ions and Metabolites Enter Mitochondria via Transporters • freely permeable only to O2, CO2, and H2O • Cytosolic Reducing Equivalents Are “Transported” into Mitochondria • Only the electrons from cytosolic NADH are transported into the mitochondrion by one of several ingenious “shuttle” systems. • the malate–aspartate shuttle • the glycerophosphate shuttle
  6. 6. A Translocator Exchanges ADP and ATP • also called the adenine nucleotide translocase • Inhibitor of the ATP–ADP translocator - atractyloside - carboxyatractyloside (CATR) - Bongkrekic acid First two inhibit from external side of IMM Third one inhibit from inner side of IMM
  7. 7. Phosphate Must Be Imported into the Mitochondrion phosphate carrier Electroneutral Pi–H+ symport driven by ΔpH
  8. 8. Formation of NADH and FADH2
  9. 9. Electron Transport Is an Exergonic Process
  10. 10. • In mitochondria electrons pass through three protein complexes. • This allows the overall free energy change to be broken into three smaller parcels, each of which contributes to ATP synthesis by oxidative phosphorylation. • Oxidation of one NADH results in the synthesis of approximately 2.5 ATP
  11. 11. Electron Carriers Operate in Sequence
  12. 12. Inhibitors Reveal the Workings of the Electron-Transport Chain. • Sequence of events elucidated largely through the use of specific inhibitors. • The rate at which O2 is consumed by a suspension of mitochondria is a sensitive measure of the activity of the electron-transport chain. • Example - rotenone ( plant toxin used as fish poison) - amytal (a barbiturate) - antimycin A (an antibiotic) - cyanide
  13. 13. Standard Reduction Potentials of Some Biochemically Important Half-Reactions
  14. 14. The mitochondrial electron-transport chain.
  15. 15. Complex I Accepts Electrons from NADH • NADH–coenzyme Q oxidoreductase • largest protein complex in the inner mitochondrial membrane • L-shaped • Complex I Contains Multiple Coenzymes - flavin mononucleotide (FMN) - eight or nine iron–sulfur clusters most common types [2Fe–2S] and [4Fe–4S] clusters • The oxidized and reduced states of all iron–sulfur clusters differ by one formal charge regardless of their number of Fe atoms.
  16. 16. [2Fe–2S] [4Fe–4S]
  17. 17. The oxidation states of FMN and coenzyme Q.
  18. 18. Complex II Contributes Electrons to Coenzyme Q • succinate–coenzyme Q oxidoreductase • Complex II Contains a Linear Chain of Redox Cofactors mushroom-shaped homotrimer • two hydrophilic subunits, a flavoprotein (Fp) and an iron–sulfur subunit (Ip) – project to mitochondrial matrix • two hydrophobic membrane-anchor subunits, CybL and CybS
  19. 19. Complex III Translocates Protons via the Q Cycle • coenzyme Q–cytochrome c oxidoreductase • Contains - two b-type cytochromes - one cytochrome c1 - one [2Fe–2S] cluster ( co-ordinated by two Histidine residue rather than cystine – known as Rieske center )
  20. 20. Electrons from Coenzyme Q Follow Two Paths • bifurcation of the flow of electrons from CoQH2 to cytochrome c1 and to cytochrome b (in which the flow is cyclic) so called Q-cycle
  21. 21. CoQH2 undergoes a two-cycle reoxidation in which the semiquinone, Co Q. , is a stable intermediate • The net reaction is the transfer of two electrons from QH2 to cytochrome c1 and the translocation of four protons from the matrix to the intermembrane space.
  22. 22. Cytochrome c Is a Soluble Electron Carrier • positively charged residues constitute binding sites for complementary negatively charged groups on cytochrome c1 and cytochrome c oxidase
  23. 23. Complex IV Reduces Oxygen to Water • Cytochrome-c oxidase • four redox centers: cytochrome a cytochrome a3 a copper atom known as CuB a pair of copper atoms known as the CuA center
  24. 24. Electron Transport Generates a Proton Gradient • Electron transport causes Complexes I, III, and IV to transport protons across the inner mitochondrial membrane from the matrix, a region of low [H+], to the intermembrane space (which is in contact with the cytosol), a region of high [H+] • The free energy sequestered by the resulting electrochemical gradient (also called the protonmotive force; pmf ) powers ATP synthesis
  25. 25. • free energy change • φ Faraday constant • ψ membrane potential
  26. 26. CLINICAL ASPECT • Fatal Infantile Mitochondrial Myopathy and renal dysfunction involves severe diminution or absence of most oxidoreductases. • MELAS ( mitochondrial encephalopathy, lactic acidosis & stroke) is an inherited condition due to NADH:Q oxidoreductase( complex-I) & cytochrome oxidase (complex-IV) deficiency.
  27. 27. THANK YOU

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