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Anaerobic Respiration |
Anaerobic Respiration
We just think that aerobic respiration is required for living beings, but humans also need anaerobic respiration when there is no oxygen supplement. Anaerobic respiration is a metabolic process that allows organisms to produce energy in the absence of oxygen. When the oxygen supply is less humans switch to anaerobic
respiration. During exercise, lactic acid is accumulated in muscle cells leading to the sensation of muscle fatigue and discomfort.
Significance of Anaerobic Respiration
It plays a vital role in various biological systems, from microbial organisms to human muscle cells. Microorganisms such as bacteria and yeast also perform this
type of respiration in the form of a process called food fermentation
The first step is glycolysis which takes place in the presence of oxygen, glucose molecule undergoes through series of steps, and the final product produced is pyruvate. For each cycle of glycolysis, two pyruvate molecules are produced. The complete glycolysis pathway is described in this article.
After glycolysis, anaerobic respiration occurs in the cytoplasm rather than in mitochondria. Anaerobic respiration takes other
substances such as minerals including sulfur, and nitrate to carry out cellular
respiration and produces less energy as compared to aerobic respiration.
The purpose of anaerobic respiration is to reserve NAD+ ions to reuse them in the glycolysis process for the continuation of ATP production. During anaerobic respiration, the reaction of pyruvate-producing lactic acid, ethanol, and carbon dioxide is convertible. However, once oxygen becomes available, lactic acid is converted back into pyruvate and further metabolized through aerobic respiration. A net total of two ATP are produced during anaerobic respiration.
Types of Anaerobic Fermentation
Lactic acid Oxidation
Lactic acid respiration is performed in human beings where pyruvate converts to lactate. Glucose is partially oxidized producing two molecules of lactic acid and 2 ATP molecules.
NADH is oxidized reducing its electrons and
transferring proton to pyruvate producing lactate. This by-product lactate is catalyzed in the presence of the enzyme lactate dehydrogenase. During this reaction, coenzyme flavin mononucleotide and cofactor Zn are also required. This lactate is converted to lactic acid by
releasing carbon dioxide and water.
Lactic acid is delivered to all the cells that are active in the body. Due to the acidic nature of lactic acid, it is converted to pyruvate for use in the TCA cycle. Liver cells uptake lactate and transform it to pyruvate, The pyruvate then produces glucose through the reverse process of glycolysis.
Alcoholic fermentation
Alcoholic fermentation occurs in plants and bacteria. Alcoholic fermentation occurs in two steps producing ethanol and carbon dioxide, and releasing energy in the form of ATP.
The first step is where NADH transfers electrons to pyruvate removing a carboxyl group from pyruvate and producing the two-carbon compound acetaldehyde. This reaction occurs in the presence of the enzyme pyruvate decarboxylase and a carbon dioxide molecule is released.
The
second step is NADH transfers electrons to acetaldehyde reducing itself to NAD+
and producing ethanol in the presence of alcohol dehydrogenase.
Applications of Anaerobic Fermentation
Microbial Applications
Anaerobic respiration is required in various biological cycles such as the carbon cycle, sulfur cycle, and nitrogen cycle to play a role in their different stages such as denitrification, and sulfur reduction. Microbial cells power themselves through anaerobic mechanisms producing electricity.
Producing alcohol and beverages
Alcohol fermentation is employed in various industrial applications. One notable example is the production of alcoholic beverages, such as wine, beer, etc. Yeast, a type of microorganism, is responsible for the conversion of sugars into alcohol during the fermentation process. Alcoholic fermentation is also utilized in the production of biofuels, as certain microorganisms can convert plant biomass into ethanol.
Manufacturing of biogas
Methane gas is produced due to the anaerobic fermentation of ethanol which helps break down biodegradable waste.
Manufacturing of dairy products
Lactic acid fermentation is employed in various industrial processes. Dairy products such as cheese, yogurt, and buttermilk are produced by lactic acid bacteria. Fermentation of propionic acid adds flavor and texture to the cheese. Fermentation of butyric acid oxidizes sugar into pyruvate releasing carbon dioxide that creates distinctive holes in the cheese.
Carbon dioxide Production
The carbon dioxide generated during alcoholic oxidation plays a crucial role in baking. Yeast is responsible for the production of carbon dioxide gas, which creates bubbles in the dough, leading to the rising effect. This process is vital in the preparation of bread, pastries, and other baked goods.
Manufacturing of vinegar
During alcohol fermentation, the final product produced is
ethanol. The microorganisms present in
Acetobacter bacteria get oxidized and convert to acetic acid. Acetic acid
contributes 6-8% of vinegar composition which adds flavors to food products and
is used to preserve food components.
Role of nitrate in the nitrogen cycle
The denitrification process in the nitrogen cycle is an anaerobic respiration mechanism where nitrate is oxidized and reduced to nitrite. Denitrification is performed by various bacteria are Bacillus, Pseudomonas, Aerobacter, etc. Denitrification helps in the treatment of wastewater by reducing nitrate to the gas form of nitrogen.
Ammonification
Lactic acid fermentation produced by anaerobic respiration causes ammonification which helps in converting nitrogen to ammonium ions or ammonia. It prevents ammonia from entering our body and causes damage to the body system.
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