Biochemical process of fermentation of sucrose
A laboratory vessel being used for the fermentation of
Fermentation of sucrose by yeast.
chemical equations below summarize the fermentation of sucrose () into ethanol (). Alcoholic fermentation converts one
glucose into two moles of ethanol and two moles of carbon dioxide, producing two moles of
ATP in the process.
The overall chemical formula for alcoholic fermentation is:
Sucrose is a
dimer of glucose and fructose molecules. In the first step of alcoholic fermentation, the enzyme
invertase cleaves the
glycosidic linkage between the glucose and fructose molecules.
Next, each glucose molecule is broken down into two
pyruvate molecules in a process known as
 Glycolysis is summarized by the equation:
CH3COCOO− is pyruvate, and Pi is inorganic
phosphate. Finally, pyruvate is converted to ethanol and CO2 in two steps, regenerating oxidized NAD+ needed for glycolysis:
- 1. CH3COCOO− + H+ → CH3CHO + CO2
- 2. CH3CHO + NADH+H+ → C2H5OH + NAD+
This reaction is catalyzed by
alcohol dehydrogenase (ADH1 in baker's yeast).
As shown by the reaction equation, glycolysis causes the reduction of two molecules of
ADP molecules are also converted to two ATP and two water molecules via
Fermentation of sugar to ethanol and CO2 can also be done by
Zymomonas mobilis, however the path is slightly different since formation of pyruvate does not happen by glycolysis but instead by the
Entner–Doudoroff pathway. Other
microorganisms can produce ethanol from sugars by fermentation but often only as a side product. Examples are