1. An evolutionary approach to learning energy metabolism
How do cells obtain energy to make ATP?
oxidation-reduction
How do cells make ATP?
oxidative phosphorylation
Images in this video are from Wikipedia, unless otherwise indicated.

2. Oxidation-reduction is the core of energy metabolism
Oxidation is the loss of electrons
Organic molecules (food) and inorganic chemical electron donors are oxidized
Reduction is the gain of electrons
The amount of free energy released depends on the reduction potential difference of the redox pair
Catabolic pathways feature a series of redox reactions (electron-transfer reactions)
NAD+/NADH is the primary electron carrier

3. Summary of respiration of glucose
C6H12O6 + 6O2  6CO2 + 6H2O C6H12O6 + 6O2 + 6H2O  6CO2 + 12H2O C is oxidized to CO2 O2 is reduced to H2O Electrons are transferred from glucose to O2 via NADH
First equation is balanced, but doesn’t tell the full story of how oxygen is reduced.

4. Oxidized and reduced forms of NAD
NAD = nicotinamide adenine dinucleotide.
For NADH + H+ +1/2 O2 ↔ NAD+ + H2O, ΔGo = kcal/mol.

5. Hydrogen powers ATP synthesis

6. Respiration: transfer of electrons from electron donors to electron acceptors to charge a membrane proton gradient
H+ electrochemical gradient H+
Electron transport chain
membrane
NADH
Terminal electron acceptors
O2, NO3-, SO42-, Mn4+, Fe3+,
CO2, etc.
NAD+
Electron donors {[CH2O], H2, H2S, CH4, Fe2+, etc.}
Diagram by J. Choi

7. Organisms may be classified by the source of energy and the source of organic carbon:
Heterotrophs – both energy and carbon come from organic molecules (food)
Autotrophs – make their own organic carbon from CO2
Photoautotrophs – energy from sunlight
Chemoautotrophs – energy from reduced inorganic molecules

8. Terminal Electron Acceptors
Different e- acceptors are used sequentially in microbial ecosystems.
O2 ∆G = -479 kJ mol-1
NO3- ∆G = -453 kJ mol-1
Mn4+ ∆G = -349 kJ mol-1
Fe3+ ∆G = -114 kJ mol-1
SO42- ∆G = -77 kJ mol-1
Use of other terminal electron acceptors than oxygen = anaerobic respiration

9. Chemiosmosis in prokaryotes
Electron transport chain generates proton gradient across membrane.
Resulting proton motive force drives ATP synthesis and active transport.
Fenchel, Origin & Early Evolution
of Life, Oxford U Press 2002, Fig 6.2
Biology 1510

10. Electron transport chain in mitochondria

11. Proton gradient powers ATP synthase during respiration (oxidative phosphorylation)F0
F0 portion in membrane
resembles flagellar motor
F1 portion (ATP synthase)
-resembles DNA helicase F1