microbiology

Fermentation is important in anaerobic conditions when there is no oxidative phosphorylation to maintain the production of ATP ( adenosine triphosphate) by glycolysis. During fermentation, pyruvate is metabolized to various compounds. Homolactic fermentation is the production of lactic acid from pyruvate; alcoholic fermentation is the conversion of pyruvate into ethanol and carbon dioxide; and heterolactic fermentation is the production of lactic acid as well as other acids and alcohols. Fermentation does not necessarily have to be carried out in an anaerobic environment.

1. Oxidative phosphorylation requires oxygen. Fermentation does not.
2. Fermentation produces lactic acid or ethanol and CO2. Oxidative phosphorylation produces CO2 and water.
3. Oxidative phosphorylation produces 18 time more ATP than fermentation.
4. Fermentation requires a sugar for "fuel." Oxidative phosphorylation can use sugars, amino acids, fatty acids and such alcohols as ethanol and glycerol as "fuel."

Fermentation and oxidative phosphorylation both produce ATP, but they differ in what they need as reagents and in their environments. Fermentation is an anaerobic process that takes place in the cytoplasm, while oxidative phosphorylation is a process that requires either oxygen or another oxidizing agent to act as the final electron acceptor and takes place in the mitochondria.

An oxidizing agent is required in oxidative phosphorylation to provide an electromotive force to drive the electron transport chain. Electrons are passed from one protein complex in the chain to the next, pumping protons from the mitochondrial matrix into the intermembrane space as this occurs. Without an oxidizing agent at the end of the chain to accept the electrons, the electrons stay within the chain with nowhere to go, and the process stops. The protons pumped into the intermembrane space power ATP synthase as they travel back into the mitochondrial matrix, producing ATP. So if the chain stops pumping protons across, eventually there won't be enough protons in the intermembrane space to generate the gradient needed to power ATP synthase, and ATP production via oxidative phosphorylation stops.

First things first, anaerobic respiration and fermentation are completely separate pathways. Aerobic and anaerobic respiration involve an electron transport chain in the membrane. In aerobic resp the terminal electron acceptor is oxygen and in anaerobic resp it is something else (e.g. nitrate, sulfate, fumerate, malate, etc). Fermentation, which occurs anaerobically, is a pathway where NADH (or some other reduced electron acceptor-generated by the pathway) gets reoxidized by the metabolites of the pathway. Basically instead of the electron carriers reoxidizing NADH, in fermentation they dispose of electron in an "electron sink," which is then excreted into the medium (e.g. alcohols, solvents, organic acids). Also, this occurs in the cytosol, not the membrane.

You are absolutely right - they are different!! Anaerobic respiration does use high energy electrons which are passed down an electron transport chain, to power the chemiosmotic synthesis of ATP. The difference is that oxygen is not used as a terminal electron acceptor. One common anaerobic acceptor is nitrate. I'm sure there are others.

The purpose of fermentation is twofold. First, pyruvate produced by glycolysis must be gotten rid of - nothing can exist in its own waste products. Secondly, the NADH produced in glycolysis must be reoxidized back to NAD+ for glycolysis to continue. Both of these are accomplished by a large number of acidic or alcoholic fermentation reactions. The big difference is that the ATP is manufactured by substrate level phosphorylation during glycolysis, rather than by oxidative phosphorylation. Fermentation uses no electron transport system and no terminal electron acceptor. In fact, to be technical about it, fermentation produces no ATP. It's the glycolytic pathway that produces the ATP.