Introduction to Metabolism

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Introduction to Metabolism Part
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• Coenzyme A CoA
• Oxidation-reduction (redox) reactions.

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Coenzyme A high energy compound Activating
molecules
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Thioester- High energy bond
Takes energy to form it.
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Can get energy out.
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Cofactors are involved in Oxidation reduction
reactions Electron carriers
Coupling energy production to energy
utilization ATP
Activating molecules Coenzyme A
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Oxidation and Reduction
Zn Cu2 ? Zn2 Cu
Oxidation Loss of electron Zn ? Zn2 2e-
Reduction Gain of electrons Cu2 2e- ? Cu
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Zn Cu2 ? Zn2 Cu
Oxidatiom-reduction Redox reactioon
In a redox reaction one partner is oxidized and
the other is reduced.
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In a redox reaction one partner is oxidized and
the other is reduced.
Oxidation of glucose C6H12O6 6O2
6 CO2 6 H2O
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In a redox reaction one partner is oxidized and
the other is reduced.
Oxidation of glucose C6H12O6 6O2
6 CO2 6 H2O
Reduction of oxygen
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Oxidation of ethanol
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Oxidation states of functional groups.
Fats
Glucose

Reduced---------------------------------?Oxidize
d
hydrocarbon hydroxyl carbonyl
carboxyl CO2
Energy is stored in reduced compounds.
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Electron carriers are Cofactors donate or
accept electrons
Metal ions (Fe2 or Cu2) 1 electron Fe3
1e- ?? Fe2
Organic cofactors NAD NADP FAD
2 electrons 1 or 2 H
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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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General rules

• 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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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 DEoel acc - DEoel don RT ln Keq
nF Where el acc electron
acceptor el don electron donor F
the Faraday 96.48 kJ/V DE DEo RT ln
Aox Bred nF
AredBox
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DGO -n F DEO
Number of electrons transferred
Potential difference
Faraday
NADH H ½ O2 ? NAD H2O
DEo 1.14 V
DGO -2 96.48 kJ/V (1.14) V -220 kJ/mol
ATP formation 32 kJ/mole
Max. amount of ATP 7 moles Reality 2.5
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Note positive DE ? negative DG spontaneous
reaction.
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Electron carriers are Cofactors donate or
accept electrons
Metal ions (Fe2 or Cu2) 1 electron Fe3
1e- ?? Fe2
Organic cofactors NAD NADP FAD
2 electrons 1 or 2 H
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How do you measure NADH formation.
Absorption spectroscopy NADH also
fluoresces.
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FADH flavin adenine dinucleotide
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• Methods for studying metabolic pathways.
• Radioactive isotopes.
• NMR (magnetic resonance imaging)
• Mutations natural and site directed
• Spectroscoy optical
• EPR, electron paramagnetic
• resonance.
• 5. Metabolic inhibitors.