Lactic Acid vs Alcoholic Fermentation
Respiration is an essential physiological activity of all living organisms by which they obtain energy for carrying out all metabolic activities of the body. The salient feature of respiration is the exchange of gases between the body and the environment. This is apparent in breathing, which is also called the external respiration. In reality, the fundamental exchange occurs in the cells and is duly called the cellular respiration. But, there are certain organisms that do not involve themselves with the uptake of oxygen for respiration, which are called anaerobes. Microorganisms such as Clostridium species and parasitic worms such as Ascaris show this kind of a respiration. There are two basic types of anaerobic respiration; they are lactic acid fermentation found in animals and alcohol fermentation found in plants and most microorganisms. During the fermentation process or the anaerobic breakdown of glucose by living cells, often production of ATP, heat, waste products and waste gasses is seen.
During alcoholic fermentation, the glucose is converted to pyruvic acid by the release of one ATP molecule and H+ ions. Then the pyruvic acid in the absence of oxygen, releases one molecule of CO2 to produce acetaldehyde. The acetaldehyde then reoxidizes NAD found in the cellular fluid by the H+ released, and is self reduced to ethanol. This process happens only in plants. The enzymes, pyruvic acid decarboxylase, and alcohol dehydrogrnase catalyses these reactions. This process forms 2 ATP molecules per glucose molecule. Therefore, the energy efficiency is about 29%.
Lactic Acid Fermentation
The lactic acid fermentation takes a similar path up to the pyruvic acid formation step. Here, the pyruvic acid is converted into lactic acid by the enzyme lactic dehydrogenase. The reducing agent is NADH2, which reoxidizes to NAD. The final product is a three carbon molecule. The net gain is 2 ATPs per glucose molecule. This method of anaerobic respiration is found in animals and lower microorganisms. The energy efficiency is about 41%.
What is the difference between Lactic Acid Fermentation and Alcoholic Fermentation?
Both Lactic acid fermentation and alcoholic fermentation are anaerobic respiratory processes. They produce 2ATP each, during the process as energy. The reducing agent is NAD+, which is regenerated in the process. Yet, Lactic acid fermentation occurs only in animal tissue and alcoholic fermentation occurs only in plant tissue. The energy efficiency of the two processes also differs; Lactic acid fermentation has 41% efficiency, and alcoholic fermentation has 29% efficiency.
In alcoholic fermentation, CO2 is split off, and two carbon compound ethyl alcohol is produced as the end product. In lactate fermentation, the end product is the three-carbon compound lactic acid. In both these processes, the end products are large organic compounds, which themselves are stores of energy. But, they are not further oxidized to release energy. Furthermore, the NAD + regeneration does not yield ATP; hence, both processes have 50% energy efficiency. These fermentation processes are used by many primitive organisms that have been evolved in Oxygen less conditions, or have developed this mechanism as a secondary survival technique like the parasitic/commensal worms in the mammalian stomach.