Energy conversion (continued)

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Lecture 26 Energy conversion (continued) Substrate
Oxidation, Generation of reduced high-energy
intermediates and their oxidation by oxygen
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http//www.microscopyu.com/galleries/fluorescence/
cells/hela/hela.html
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Why oxygen? Electron re-distribution from less
electronegative to more electronegative atoms
occurs with massive energy release Electronegati
vity of common elements H lt C lt S lt N lt O Cl lt
F
Identify the substance and the reduction state of
the first carbon (red)
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Enthalpies of oxidation (combustion) hydrogen
(MW 2) H2 ½O2 ? H2O -286 kJ/mol (-68.4
kCal/mol) methane (MW 16) CH4 3O2 ? CO2
2H2O -891 kJ/mol (213) glucose (MW
180.2) C6H12O6 6O2 ? 6CO2 6H2O -2840
kJ/mol (-680) palmitic acid (MW
256.4) C16H32O2 31O2 16CO2 16H2O -
9730 kJ/mol (-2328)
Compare caloric capacities of the substrates
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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
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Reduction potentials for mixtures of
reductant/oxidant (hlf-reaction potentials) are
measured using the standard hydrogen electrode
2H 2e ? H2
Mg2 2e ? Mg (metal)
http//www.chemguide.co.uk/physical/redoxeqia/eomg
diag.gif
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Standard Reduction potentials for some
half-reactions, Volt ½ O2 2H 2e ?
H2O 0.816 Fe3 e ? Fe2 0.771 Cytochrom
e c (Fe3) e ? Cytochrome c (Fe2)
0.254 Fumarate2- 2H 2e ? succinate2- 0.031
2H 2e ? H2 (standard condition) 0 Pyruvate
2H 2e ? lactate -0.185 FAD 2H 2e ?
FADH2 -0.219 S 2H 2e ?
H2S -0.243 NAD H 2e ?
NADH -0.320 NADP H 2e ?
NADPH -0.324 a-ketoglutarate CO2 2H 2e ?
isocytrate -0.38 2H 2e ? H2 (pH 7) -0.414
Standard Reduction potentials for some
half-reactions, Volt ½ O2 2H 2e ?
H2O 0.816 Fe3 e ? Fe2 0.771 Cytochrom
e c (Fe3) e ? Cytochrome c (Fe2)
0.254 Fumarate2- 2H 2e ? succinate2- 0.031
2H 2e ? H2 (standard condition,
pH0) 0 Pyruvate 2H 2e ? lactate -0.185 FAD
2H 2e ? FADH2 -0.219 S 2H 2e ?
H2S -0.243 NAD H 2e ?
NADH -0.320 NADP H 2e ?
NADPH -0.324 a-ketoglutarate CO2 2H 2e ?
isocytrate -0.38 2H 2e ? H2 (pH 7) -0.414
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NADH H ½ O2 ? NAD H2O
NAD H 2e ? NAD -0.320 V
½ O2 2H 2e ? H2O 0.816 V
total difference 1.14 V
DG -nFEo -220 kJ/mol
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Stage 1 (in the cytosol)
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NAD
NAD H 2e- NADH
half reaction (-0.32 V)
FAD has smaller reducing potential (-0.219 V) so
its reduction can be coupled to a less
energetically favorable oxidation reaction
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Beta-Oxidation of fatty acids
R CH3-(CH2)n-
R CH3-(CH2)n-2-
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When succinate and oxygen are given to
mitochondria, they release H
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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
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Iron-sulfur cluster (Fe-S)
Heme
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CoQ accepts both electrons and protons
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Why add valinomycin?
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What conditions are necessary for the experiment
to work?

• poorly-buffered medium
• Valinomycin/potassium
• A substrateNOT NADHas stated in your book

Is ATP synthesis the reason for the pH returning
to the original value?...
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Oxidation rate is slow
Why?
Oxidation rate is fast
Why?
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