Fermentation is a catabolic process which takes place in the cytoplasm of any cell where sugar is broken down into either lactic acid or ethyl alcohol. Fermentation is an anaerobic process meaning it occurs in the absence of oxygen. First a sugar, typically glucose goes through glycolysis, this creates 2 pyruvic acid molecules, 2 ATP molecules are also synthesized from 2ADP. 2 NADH molecules are also present from glycolysis during fermentation. If an organism were aerobic the pyruvic acid molecules produced would continue through cellular respiration to produce even more ATP, however in anaerobic organisms, or those without oxygen, the process of fermentation occurs.
During alcohol fermentation CO2 is released which creates 2 molecules of Acetaldehyde, after this the hydrogen from the 2 molecules of NADH are released and bound to the Acetaldehyde. This creates 2 molecules of ethanol or ethyl alcohol.
Glucose (C6H12O6) + 2ADP (C10H15N5O10P2) +2NAD (C21H27N7O14P2)—> 2ATP (C10H16N5O13P3) + 2NADH (C21H28N7O14P2) + 2Pyruvate (C3H3O3) -Glycolysis
2Pyruvate (C3H4O3)—> CO2 + 2Acetaldehyde (C2H4O)
2Acetaldehyde (C2H4O) + 2NADH (C21H28N7O14P2) —> 2NAD (C21H27N7O14P2) + 2Ethanol (C2H6O)
During lactic acid fermentation, no CO2 is released, 2 Pyruvate is converted to 2 Lactate with the help of 2 molecules of NADH.
Glucose (C6H12O6) + 2ADP (C10H15N5O10P2) +2NAD (C21H27N7O14P2)—> 2ATP (C10H16N5O13P3) + 2NADH (C21H28N7O14P2) + 2Pyruvate (C3H3O3)
2Pyruvate (C3H3O3) + 2NADH (C21H28N7O14P2)—> 2NAD (C21H27N7O14P2) + 2Lactate (C3H6O3)
Ultimately fermentation itself doesn’t create any energy, and only creates the by-products of either lactic acid or ethyl alcohol, fermentation however regenerates NAD+ which is required to create small amounts of ATP during glycolysis. Energy transfers occur when the glucose is first broken down into pyruvate molecules, the energy stored within the chemical bonds of the glucose is then released and used to form ATP, before this can happen however the reaction must first be kick-started, so two molecules of ATP are expended to reach the activation energy of this reaction. After this occurs, four molecules of ATP are created from the energy released by the glucose, this results in a net gain of 2 ATP molecules. These are essentially the only real energy transfer which happens through fermentation as the rest of fermentation simply occurs to allow glycolysis to take place again. However throughout fermentation several atoms and their electrons are also transferred between molecules, an example of this is how an H+ atom is transferred between NADH and NAD, as the atom itself contains energy, these kinds of transfers could also be considered energy transfers.
By Kishav Changar and Lee Cadotte