1. Lecture 26
Energy conversion (continued)
Substrate Oxidation, Generation of reduced high-energy intermediates and their oxidation by oxygen

2. http://www. microscopyu. com/galleries/fluorescence/cells/hela/hela

3. Why oxygen? H < C < S < N < O …Cl < F
Electron re-distribution from less electronegative to more electronegative atoms occurs with massive energy release:
Electronegativity of common elements:
H < C < S < N < O …Cl < F
Identify the substance and the reduction state of the first carbon (red)

4. Enthalpies of oxidation (combustion)
hydrogen (MW 2)
H2 + ½O2 → H2O kJ/mol
(-68.4 kCal/mol)
methane (MW 16)
CH4 + 3O2 → CO2 + 2H2O kJ/mol
(213)
glucose (MW 180.2)
C6H12O6 + 6O2 → 6CO2 + 6H2O kJ/mol
(-680)
palmitic acid (MW 256.4)
C16H32O O2 – 16CO2 + 16H2O kJ/mol
(-2328)
Compare caloric capacities of the substrates

5. Oxidation-reduction (Red-ox) reactions usually lead to re-distribution of electron densities or complete transfer of electrons resulting in change of ionization state.
Fe2+ + Cu2+ → Fe3+ + Cu+
or in the form of half-reactions: Fe2+ → Fe3+ + e
Cu2+ + e → Cu+
In biological systems oxidation is often coupled to dehydrogenation.
1. Direct transfer of electrons
2. As a transfer of H atoms or removal of H atoms coupled to production of H+
3. As a Hydride ion :H–
4. Through direct combination with oxygen
R-CH3 + (½)O2 → R-CH2-OH

6. Reduction potentials for mixtures of reductant/oxidant (hlf-reaction potentials) are measured using the standard hydrogen electrode
2H+ + 2e → H2
Mg2+ + 2e → Mg (metal)

7. Standard Reduction potentials for some half-reactions, Volt
½ O2 + 2H+ + 2e → H2O
Fe3+ + e → Fe
Cytochrome c (Fe3+) + e → Cytochrome c (Fe2+)
Fumarate2- +2H+ + 2e → succinate
2H+ + 2e → H2 (standard condition, pH0) 0
Pyruvate + 2H+ + 2e → lactate
FAD + 2H+ + 2e → FADH
S + 2H+ + 2e → H2S
NAD+ + H+ + 2e → NADH
NADP+ + H+ + 2e → NADPH
α-ketoglutarate + CO2 + 2H+ + 2e → isocytrate -0.38
2H+ + 2e → H2 (pH 7)
Standard Reduction potentials for some half-reactions, Volt
½ O2 + 2H+ + 2e → H2O
Fe3+ + e → Fe
Cytochrome c (Fe3+) + e → Cytochrome c (Fe2+)
Fumarate2- +2H+ + 2e → succinate
2H+ + 2e → H2 (standard condition) 0
Pyruvate + 2H+ + 2e → lactate
FAD + 2H+ + 2e → FADH
S + 2H+ + 2e → H2S
NAD+ + H+ + 2e → NADH
NADP+ + H+ + 2e → NADPH
α-ketoglutarate + CO2 + 2H+ + 2e → isocytrate -0.38
2H+ + 2e → H2 (pH 7)

8. NADH + H+ + ½ O2 → NAD+ + H2O
NAD+ + H+ + 2e → NAD V
½ O2 + 2H+ + 2e → H2O V
total difference V
DG = -nFEo = -220 kJ/mol

11. Stage 1
(in the cytosol)

15. NAD
NAD+ + H+ +2e NADH
half reaction (-0.32 V)
FAD has smaller reducing potential ( V) so its reduction can be coupled to a less energetically favorable oxidation reaction

22. Beta-Oxidation of fatty acids
R= CH3-(CH2)n-
R= CH3-(CH2)n-2-

23. When succinate and oxygen are given to mitochondria, they release H+

24. Electron transport chain
Complex I II III IV
Energy released in forming water is stored as a PMF
Energy is divided into smaller units ~10-12 protons per water molecule

25. Iron-sulfur cluster (Fe-S)
Heme

27. CoQ accepts both electrons and protons

31. Why add valinomycin?

32. What conditions are necessary for the experiment to work?
poorly-buffered medium
Valinomycin/potassium
A substrate…NOT NADH…as stated in your book
Is ATP synthesis the reason for the pH returning to the original value?...

34. Oxidation rate is slow
Why?
Oxidation rate is fast
Why?