Chapter 17 Electron Transport and

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Chapter 17 Electron Transport and Oxidative
Phosphorylation. - I
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Glycolysis and the citric acid cyle produced 6
CO2 10 NADH 2 FADH2 4 ATP per glucose oxidized.
Energy rich electrons.
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Reduced electron carriers
Glycolysis 2 NADH
Pyruvate dehydogenase 2 NADH
Citric acid cycle 6 NADH 2
FADH2
Total 10 NADH
2 FADH2
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• Steps in electron transport and phosphorylation
• Electron transport
• H ion transport
• ATP formation

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Mitochondria
Internal membrane cristae Electron transport,
H ion transport ATP
formation
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Electron Transport
Energy-rich electrons are passed down
the electron transport chain and
eventually react with O2.
NADH H ½ O2 ? NAD H2O Energy
Oxidation reduction reaction
NADH H ? NAD 2e- 2 H
½ O2 2e- 2 H ? H2O
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The energy is released in a series of step an
electron transport chain.
Some of the energy released is conserved as ATP
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High energy
Electron carriers
NADH
H2O
O2
Low energy
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How can we determine how much energy is released
upon the oxidation of NADH? Measure the
potential in volts.
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Free energies are related to potentials
Ethanol ? Acetaldehyde 2 e-
Sample
Reference
2 H 2e- ? H2
Standard Hydrogen Electrode (pH 7)
- 0.2 V
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Fumerate? succinate
0.03 V
Electron Flow
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Table 17.1 Standard Reduction Potentials
Standard measured against the standard
hydrogen electrode at pH 7
Reduction all written as a reduction
Xox e- ? Xred
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General rules - Table 17.1

• Negative potential
• Easy to oxidize, difficult to reduce
• Positive potential
• Easy to reduce, difficult to oxidize.

• Negative potential
• Store energy in the reduced form.

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• A compound with a more negative
• potential can reduce something with
• a more positive potential.

NAD 2e- 2 H ?? NADH H Eo -0.32V ½
O2 2e- 2 H ?? H2O Eo
0.8V
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Calculate the potential difference for the
reaction NADH H ½ O2 ? NAD H2O
Two half reactions. NAD 2e- 2 H ? NADH
H Eo -0.32 V
½ O2 2e- 2 H ? H2O
Eo 0.82 V
Reverse the NADH reaction
NADH H ? NAD 2e- 2 H

Eo 0.32 V
DEo 1.14 V
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FADH2 ½ O2 ? FAD H2O
FAD 2e- 2 H ? FADH2 Eo 0 V
½ O2 2e- 2 H ? H2O Eo 0.82 V
FADH2 ? FAD 2e- 2 H Eo -0 V
FADH2 ½ O2 ? FAD H2O DEo 0.8 V
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DGO -n F DEO
Number of electrons transferred
Potential difference
Faraday 23.2 kcal/mol
NADH H ½ O2 ? NAD H2O
DEo 1.14 V
DGO 2 23.2 (1.14) 53 kcal/mole
ATP formation 7.3 kcal/mol
Max. amount of ATP gt 7 moles Reality 3
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General Principles
High Energy
Low Energy
DEo - negative
DEo - positive
NAD/NADH
O2/ H2O
Easy to oxidize (spontaneous)
Easy to reduce
Reduced by compounds with a negative DEo
Requires energy to reduce
Energy obtain from oxidation of glucose
Energy is released which is used to make ATP
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DEo - negative high energy NADH
FADH2
DEo positive low energy O2
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Electron carriers carry only electrons e-
- Fe Cu
Fe3 e- ? Fe2
Heme proteins cytochromes (cyt)
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Cytochromes
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Hydrogen carriers carry hydrogen atoms
2 e- 2 H
NAD, FAD, CoQ
add
Coenzyme Q (CoQ)
Remove 2 e- 2 H
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4 complexes
I
II
III
IV
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Mitochondria
Internal membrane cristae Electron transport,
H ion transport ATP
formation
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Intermembrane space
e-
I III
IV
Ccyt c
CoQ
NADH
O2
Matrix
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Take home lessions

• The energy rich electrons are
• passed down an electron transport chain.

• From electron carrier to electron
• carrier.

3. Until they reach O2 producing H2O

• Energy is released which is conserved
• as ATP.

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Electron carriers Carry electrons
cytochromes Fe3 1e- ? Fe2 cyt b, cyt c, cyt
aa3 Carry electrons hydrogens CoQ 2e- 2H
? CoQH2 NADH, NADPH, FADH2, FMNH2