OXPHOS

Electron transport chain

Oxidative phosphorylation

The tale thus far….

• From one glucose molecule we have– ATPs– NADHs

– FADH2s

– 6CO2

(4)

(10)

(2)

C6H12O6 + 6O2 6CO2 + 6H2O + energy(ATP)

Redox reactions

• Reduction—gains electrons

• Oxidation—loses electrons

• In biological systems, protons often accompany the electrons.

Reduction Potentials

High Eo' indicates a strong tendency to be reduced

Go' = -nF Eo'

Eo' = Eo'(acceptor) - Eo'(donor)

Electrons are donated by the half reaction with the more negative reduction potential and are

accepted by the reaction with the more positive reduction potential: Eo’ positive, Go' negative

See table 14-2, pg. 429

Example:Half reactions:

NAD+ NADH 2 electrons Eº'= -0.32 voltsO2 H20 2 electrons Eº'= +0.816 volts

Which will be the electron acceptor? Oxygen

Eo' = Eo'(acceptor) - Eo'(donor)Eo'= 0.816-(-0.32)= 1.136 V

Go' = -nF Eo'Go' = -2(23,062 cal/mol-V)(1/136 V)

Go' = -52.4 kcal/mole

NADH vs. FADH2

Half reactions:

NAD+ NADH 2 electrons Eº'= -0.32 volts

FAD FADH2 2 electrons Eº'= -0.18 volts

O2 H20 2 electrons Eº'= +0.816 volts

Is more energy or less released in the reoxidation of FAD than NAD+?

Less, so fewer ATP's are ultimately made

The tale thus far….

• From one glucose molecule we have– A proton gradient

– 6CO2

– 6H2O

C6H12O6 + 6O2 6CO2 + 6H2O + energy(ATP)

The Chemiosmotic Theory

• Peter Mitchell (1961)

• Proton gradient drives ATP synthese

• Thus, electron transport is "coupled" to ATP synthesis by the proton gradient

Evidence• Electron transport pumps protons• Complexes are asymmetric in membrane• Membranes with complexes I-IV will do

electron transport, but…..• Need an intact membrane for oxphos• Decoupling reagents allow electron transport

but not oxphos• Proton gradient is steep enough to drive ATP

synthesis (I.e., there's enough energy)• Artificial proton gradients work just fine

How?

• F1/Fo ATPase– Makes ATP from ADP and Pi– Can also do the reverse reaction

• ATPase activity

Early evidence ….

Grand Totals (in theory)

From one glucose molecule we have

– 4 ATPs

–10 NADHs 30 ATPs

–2 FADH2s 4 ATPs

Total = 38 ATP/glucose

But in reality

Proton gradient used for many things

Cytoplasmic NADH

Reality

~ 30 ATP/glucose