Electron Transport Chain (ETC)
General Overview
* ETC is located in inner mitochondrial membrane.
* Transfer of electrons from one protein complex to the next in the ETC is called oxidation-reduction (or, redox).
* NADH yields more ATP than FADH2 because it enters the ETC at complex I.
* NADH and FADH2 enter the chain and get oxidised, reducing the complex (ie. electrons are tranferred from NADH to the complex).
* The reduced complex becomes oxidised by transferring the electrons to the next complex, which in turn becomes reduced.
* As each complex is reduced, it pumps 2 protons from the matrix into the intermembrane space.
* The last electron acceptor is O (oxygen), which becomes reduced and reacts with 2 protons to form H2O.
* There is now a gradient across the inner mitochondrial membrane and the protons will flow down this gradient through ATP synthase back into the matrix, releasing energy which is used to synthesise the ATP from ADP in the matrix.
** FOR EVERY 2 PROTONS THAT FLOW THROUGH ATP SYNTHASE, 1 ATP IS MADE. **
NADH supplies enough energy to make 3 ATP's because it enter the ETC through complex I. The electrons flow through the entire chain, pumping 2 protons through each of the complexes I, III and IV.
FADH2 only supplies enough energy to make 2 ATP because it enters the ETC at complex II. The electrons flow through the rest of the chain, pumping 2 protons through each of the complexes III and IV.

Inhibition of ETC results in lactic acidosis - why?
* anaerobic (without oxygen) conditions can't run ETC
* NADH and FADH2 can't be oxidised at the ETC, so these get backed up. NADH and FADH2 levels increase, thus NAD+ and FADH is low.
* glycolysis can still run without oxygen, producing pryuvate. Since PDH is inhibited, the pyruvate will accumulate.
* lactic acid cycle kicks in to deal with this: lactate dehydrogenase converts pyruvate to lactate while oxidising NADH to NAD+, which is used to continue running glycolysis so the cell can make small quantities of ATP (this is the actual goal).
* build up of lactate, as a byproduct of this, results in lactic acidosis (ie. blood pH lowers).

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General overview