Anaerobic
Anaerobic
The term anaerobic refers to living processes (usually the release of energy from nutrients) that take place in the absence of molecular oxygen. The earliest organisms, the prokaryotic bacteria (prokaryotes are organisms whose genetic material is not contained within a specialized nuclear membrane), likely lived in environmental niches that contained low or no levels of oxygen. The organisms extracted energy from organic compounds without oxygen (that is, by anaerobic respiration). Many organisms alive today extract their energy from nutrients aerobically (in the presence of oxygen) although a few respire. Aerobic respiration releases a lot of energy from nutrients, whereas anaerobic respiration releases relatively little energy.
Anaerobic organisms
Microorganisms that cannot tolerate oxygen and are killed in its presence are called obligate (or strict) anaerobes. Bacteria of the genus Clostridium, which cause gas gangrene, tetanus, and botulism, belong to this group, as well as Bacteroides gingivalis, which thrives in anaerobic crevices between the teeth. Strict anaerobes are killed by oxygen, which is why hydrogen peroxide (which releases oxygen) is frequently applied to wounds. Methane-producing bacteria (methanogens) can be isolated from the anaerobic habitats of swamp sludge sewage and from the guts of certain animals. Methanogens generate the marsh gases of swamps and sewage treatment plants by converting hydrogen and carbon dioxide gases to methane. Some organisms, such as yeast, have adapted to grow in either the presence or absence of oxygen and are termed facultative anaerobes.
Anaerobic respiration
All cells carry out the process of glycolysis, which is an example of anaerobic respiration. Glycolysis is the initial phase of cellular respiration that involves the splitting of the six-carbon glucose molecule into two three-carbon pyruvate fragments. This is the main energy-releasing pathway that occurs in the cytoplasm of all prokaryotes and eukaryotes, and no oxygen is required. During glycolysis, oxidation (the removal of electrons and hydrogen ions) is facilitated by the coenzyme NAD+(nicotinamide adenine dinucleotide), which is then reduced to NADH. Only two ATP molecules result from this initial anaerobic reaction. This is a small amount of energy when compared to the net aerobic energy yield of 36 ATP in the complete oxidation of one molecule of glucose.
Fermentation
Under anaerobic conditions, the pyruvate molecule can follow other anaerobic pathways to regenerate the NAD+necessary for glycolysis to continue. These include alcoholic fermentation and lactate fermentation. In the absence of oxygen, the further reduction or addition of hydrogen ions and electrons to the pyruvate molecules that were produced during glycolysis is termed fermentation. This process recycles the reduced NADH to the free NAD+coenzyme which once again serves as the hydrogen acceptor, enabling glycolysis to continue. Alcoholic fermentation, characteristic of some plants and many microorganisms, yields alcohol and carbon dioxide as its products. Yeast is used by the biotechnology industries to generate carbon dioxide gas necessary for bread making and in the fermentation of hops and grapes to produce alcoholic beverages. Depending on the yeast variety used, the different alcohol levels realized act as a form of population control by serving as the toxic element that kills the producers. Birds have been noted to fly erratically after they have gorged themselves on the fermenting fruit of the Pyracantha shrub.
Reduction of pyruvate by NADH to release the NAD+necessary for the glycolytic pathway can also result in lactate fermentation, which takes place in some animal tissues and in some microorganisms. Lactic acid-producing bacterial cells are responsible for the souring of milk and production of yogurt. In working animal muscle cells, lactate fermentation follows the exhaustion of the ATP stores. Fast twitch muscle fibers store little energy and rely on quick spurts of anaerobic activity, but the lactic acid that accumulates within the cells eventually leads to muscle fatigue and cramp.
Anaerobic
Anaerobic
The term anaerobic refers to living processes (usually the release of energy from nutrients ) that take place in the absence of molecular oxygen . The earliest organisms, the prokaryotic bacteria , lived in an oxygen deficient atmosphere and extracted energy from organic compounds without oxygen (that is, by anaerobic respiration ). Most organisms alive today extract their energy from nutrients aerobically (in the presence of oxygen) although a few respire. Aerobic respiration releases a lot of energy from nutrients, whereas anaerobic respiration releases relatively little energy.
Anaerobic organisms
Microorganisms that cannot tolerate oxygen and are killed in its presence are called obligate (or strict) anaerobes. Bacteria of the genus Clostridium, which cause gas gangrene , tetanus , and botulism , belong to this group as well as Bacteroides gingivalis, which thrives in anaerobic crevices between the teeth. Strict anaerobes are killed by oxygen, which is why hydrogen peroxide (which releases oxygen) is frequently applied to wounds. Methane-producing bacteria (methanogens), can be isolated from the anaerobic habitats of swamp sludge sewage and from the guts of certain animals. Methanogens generate the marsh gases of swamps and sewage treatment plants by converting hydrogen and carbon dioxide gases to methane. Some organisms, such as yeast , have adapted to grow in either the presence or absence of oxygen and are termed facultative anaerobes.
Anaerobic respiration
All cells carry out the process of glycolysis , which is an example of anaerobic respiration. Glycolysis is the initial phase of cellular respiration that involves the splitting of the six-carbon glucose molecule into two three-carbon pyruvate fragments. This is the main energy-releasing pathway that occurs in the cytoplasm of all prokaryotes and eukaryotes, and no oxygen is required. During glycolysis, oxidation (the removal of electrons and hydrogen ions) is facilitated by the coenzyme NAD+ (nicotinamide adenine dinucleotide), which is then reduced to NADH. Only two ATP molecules result from this initial anaerobic reaction. This is a small amount of energy when compared to the net aerobic energy yield of 36 ATP in the complete oxidation of one molecule of glucose.
Fermentation
Under anaerobic conditions, the pyruvate molecule can follow other anaerobic pathways to regenerate the NAD+ necessary for glycolysis to continue. These include alcoholic fermentation and lactate fermentation. In the absence of oxygen the further reduction or addition of hydrogen ions and electrons to the pyruvate molecules that were produced during glycolysis is termed fermentation. This process recycles the reduced NADH to the free NAD+ coenzyme which once again serves as the hydrogen acceptor enabling glycolysis to continue. Alcoholic fermentation, characteristic of some plants and many microorganisms, yields alcohol and carbon dioxide as its products. Yeast is used by the biotechnology industries to generate carbon dioxide gas necessary for bread-making and in the fermentation of hops and grapes to produce alcoholic beverages. Depending on the yeast variety used, the different alcohol levels realized act as a form of population control by serving as the toxic element which kills the producers. Birds have been noted to fly erratically after they have gorged themselves on the fermenting fruit of the Pyracantha shrub.
Reduction of pyruvate by NADH to release the NAD+ necessary for the glycolytic pathway can also result in lactate fermentation, which takes place in some animal tissues and in some microorganisms. Lactic acid-producing bacterial cells are responsible for the souring of milk and production of yogurt. In working animal muscle cells, lactate fermentation follows the exhaustion of the ATP stores. Fast twitch muscle fibers store little energy and rely on quick spurts of anaerobic activity, but the lactic acid that accumulates within the cells eventually leads to muscle fatigue and cramp.
anaerobic
Neil C. Spurway
See exercise; lactate threshold; metabolism.
Anaerobic
Anaerobic
This term refers to an environment lacking in molecular oxygen (O2), or to an organism, tissue, chemical reaction, or biological process that does not require oxygen. Anaerobic organisms can use a molecule other than O2 as the terminal electron acceptor in respiration . These organisms can be either obligate, meaning that they cannot use O2, or facultative, meaning that they do not require oxygen but can use it if it is available.
Organic matter decomposition in poorly aerated environments, including water-logged soils, septic tanks, and anaerobically-operated waste treatment facilities, produces large amounts of methane gas. The methane can become an atmospheric pollutant, or it may be captured and used for fuel, as in "biogas"-powered electrical generators. Anaerobic decomposition produces the notorious "swamp gases" that have been reported as unidentified flying objects (UFOs).
anaerobic
anaerobic
1. Of an environment: one in which air (oxygen) is absent. In the case of a depositional environment, one with 0.0–0.1 ml of dissolved oxygen per litre of water. Compare AEROBIC; and DYSAEROBIC.
2. Of an organism: one able to grow only in the absence of oxygen, i.e. an anaerobe.
2. Of a process: one that can occur only in the absence of oxygen.
anaerobic
1. Of an environment: one in which oxygen is absent.
2. Of an organism: one able to exist only in the absence of oxygen, i.e. an anaerobe. Organisms may be facultative anaerobes (e.g. yeasts) or obligatory anaerobes (e.g. sulphur bacteria).
3. Of a process: one that can occur only in the absence of oxygen.
anaerobic
1. Of an environment: one in which oxygen is absent.
2. Of an organism: one able to exist only in the absence of oxygen, i.e. an anaerobe. Organisms may be facultative anaerobes (e.g. yeasts) or obligatory anaerobes (e.g. sulphur bacteria).
3. Of a process: one that can occur only in the absence of oxygen.