1. Oxidative Phosphorylation
Recall the four metabolic regions of the mitochondrion:

2. Oxidative Phosphorylation
We saw Krebs’ Cycle happen in the Matrix. Now, the NADH & FADH2 produced there ‘taxi’ electrons to the CRISTAE… the mitochondrial Inner membrane & intermembrane space are used in oxidative phosphorylation.

3. Two Phases: ELECTRON TRANSPORT Phase:
Causes an accumulation of protons in the intermembrane space
ATP SYNTHESIS Phase:
Protons are used to form ATP

4. Electron Transport Chain
A series of proteins embedded in the inner membrane.

5. Electron Transport Chain
NADH from Krebs “taxis” 2 electrons to complex 1.
As electrons go down the chain, they cross the membrane back & forth 3 times. Each time, 2 protons H+ follow along.
At the end of the chain, the electrons combine with O2 and H+ to form water.

6. Electrochemical Gradient:
The movement of electrons, and subsequent movement of H+, results in a high concentration of H+ in the intermembrane space. This creates a gradient of both chemical concentration & electric (ionic) charge

7. Electrochemical Gradient:
This gradient means that H+ will tend to diffuse back out into the matrix. This movement is called CHEMIOSMOSIS.
But, being charged ions, they can’t simply pass through the membrane bilayer. They need a ’passage way’ – a membrane protein channel.

8. ATP Synthetase (Synthase)
That ‘passage way’ is the ATP Synthetase membrane protein complex. It allows 2H+ through and, energized by their charge, changes shape to accommodate 1 ADP + Phosphate; it catalyzes the synthesis of 1 ATP.

9. Energy Yield:
NADH takes advantage of the full chain. This means 6H+ cross the membrane, and ultimately 3 ATP are made.
FADH2 misses the first step; 4H+ cross, 2 ATP are made.
NADH from glycolysis also only result in 2 ATP forming.

10. Putting it all together: