Detailed Summary of Fermentation
Fermentation is a biochemical process that occurs anaerobically, meaning it happens in the absence of oxygen. During this process, glucose undergoes partial oxidation to produce energy in the form of ATP, albeit significantly less than that produced through aerobic respiration. The key initial substrate in fermentation is pyruvic acid, which is generated from glycolysis, the breakdown of glucose.
In yeasts, for example, fermentation converts pyruvic acid into carbon dioxide (CO2) and ethanol through the action of specific enzymes such as pyruvic acid decarboxylase and alcohol dehydrogenase. During this process, NADH is oxidized back to NAD+, which is crucial for sustaining glycolysis so that energy can continue to be produced, even in the absence of oxygen.
In animal cells, particularly muscle cells during intense exercise, pyruvic acid is converted into lactic acid through the action of lactate dehydrogenase. This conversion allows the regeneration of NAD+ but can lead to an accumulation of lactic acid, resulting in muscle fatigue.
Overall, fermentation is characterized by the following points:
- It leads to a much lower energy yield compared to aerobic respiration—less than 7% of the energy in glucose is captured as ATP.
- The byproducts of fermentation (alcohol or lactic acid) can be toxic to the organisms producing them if they accumulate beyond certain levels—in yeasts, for instance, alcohol concentrations exceeding approximately 13% are lethal.
Thus, while fermentation serves as a critical energy-producing process under anaerobic conditions, it is less efficient than aerobic respiration and produces byproducts that can inhibit further cellular processes.