Anaerobic respiration fermentation

Hydrogen sulfide is produced during anaerobic respiration (fermentation). Anaerobic respiration enables organisms, primarily bacteria and other microbes, to meet their energy needs using sulfate, elemental sulfur, and sulfur compounds as electron acceptors instead of oxygen. 

Keywords Aerobic respiration Anaerobic respiration fermentation Redox homeostasis... 

These energy-producing reactions are termed respiration processes. They require the presence of an external compound that can serve as the terminal electron acceptor of the electron transport chain. However, under anaerobic conditions, fermentation processes that do not require the participation of an external electron acceptor can also proceed. In this case, the organic substrate undergoes a balanced series of oxidative and reductive reactions, i.e., organic matter reduced in one step of the process is oxidized in another. 

In the case of fermentation, the carbon and energy source is broken down by a series of enzyme-mediated reactions that do not involve an electron transport chain. In aerobic respiration, the carbon and energy source is broken down by a series of enzyme-mediated reactions in which oxygen serves as an external electron acceptor. In anaerobic respiration, the carbon and energy source is broken down by a series of enzyme-mediated reactions in which sulfates, nitrates, and carbon dioxide serve... 

Hydrogenase isoenzymes are also common among the metabolically more versatile bacteria (see Chapter 2). For instance, H2 metabolism and isoenzyme composition in enteric bacteria, including Escherichia coli and Salmonella typhimurium, appear to be differentially regulated under the two modes of anaerobic life, fermentation and anaerobic respiration (Table 3.1). Furthermore, biosynthesis of the individual isoenzymes appears to be controlled at a global level by the quality of the carbon source. 

Regardless of the source, phenolic acids are ultimately broken down to gaseous products such as CO2 and methane. This breakdown occurs by three general methods (i) aerobic respiration, using molecular oxygen as an electron acceptor, the end product being CO2, (ii) anaerobic respiration with electron acceptors such as nitrate and (iii) anaerobic fermentation with phosphorylation reactions involving no external electron acceptor (50). 

The existence of mitochondrial DNA, ribosomes, and tRNAs supports the hypothesis of the endosymbiotic origin of mitochondria (see Fig. 1-36), which holds that the first organisms capable of aerobic metabolism, including respiration-linked ATP production, were prokaryotes. Primitive eukaryotes that lived anaerobically (by fermentation) acquired the ability to carry out oxidative phosphorylation when they established a symbiotic relationship with bacteria living in their cytosol. After much evolution and the movement of many bacterial genes into the nucleus of the host eukaryote, the endosymbiotic bacteria eventually became mitochondria. 

The anaerobic respiration that lakes place in the muscles of higher animals, when insufficient oxygen is available for a complete breakdown of lhe lond. is also called fermentation. Lactic acid and carbon dioxide are the products of this type of fermentation. 

Lactate is an important marker compound in many biomedical, food and beverage applications. Blood lactate is monitored in exercise control and sports medicine, and D-lactate is an indicator of bacterial activity in wine fermentation [59,60,63]. Lactate produced from anaerobic respiration of cattle muscle subsequent to slaughter has been investigated as an indicator of meat freshness [62],... 

B is correct. Fermentation is anaerobic respiration. The passage states that (S)-2-methyi-l-butanol is the product of the fermentation of yeast. Looking at this molecule (above right), we prioritize the groups around the chiral carbon. Since the lowest priority group (the proton) is projected sideways, we must reverse the direction of our prioritization circle. This gives us the S configuration. 

Anaerobic respiration only has two steps glycolysis and fermentation. Glycolysis again converts glucose into pyruvate. But in the absence of oxygen, fermentation converts pyruvate into ethanol, lactic acid, or a variety of other products, depending on the organism involved. 

The fermentation (anaerobic respiration) of glucose by yeast can be represented by the following equation. The reaction is catalysed by the enzyme, zymase. After a few days the reaction stops. It has produced a 12% aqueous solution of ethanol. 

When SO42- is depleted and methanogenesis is the dominant form of anaerobic respiration, it can proceed through either of the following two pathways fermentation or C02 reduction. 

Organisms with anaerobic mitochondria can be divided into two different types those which perform anaerobic respiration and use an alternative electron acceptor present in the environment, such as nitrate or nitrite, and those which perform fermentation reactions using an endogenously produced, organic electron acceptor, such as fumarate (Martin et al. 2001 Tielens et al. 2002). An example of the first type is the nitrate respiration that occurs in several ciliates (Finlay et al. 1983), and fungi (Kobayashi et al. 1996 Takaya et al. 2003), which use nitrate and/or nitrite as the terminal electron acceptor of their mitochondrial electron-transport chain, producing nitrous oxide as... 

High yield of ATP from aerobic respiration made possible the development of typically eukaryotic features (Vellai et al. 1998). It is suggested that the last common ancestor of all eukaryotes was an aerobically respiring organism capable of complete oxidation of carbohydrates to carbon dioxide and water. Some unicellular eukaryotes have either retained or secondarily acquired the ability for anaerobic respiration and hydrogen-evolving fermentation, which has allowed their adaptation to life under microaerophilic or anaerobic conditions. 

That is why anaerobic respiration, based on nitrate as a terminal electron acceptor, is more similar to oxygen-based (aerobic) respiration than it is to fermentation and is why it must by definition be clearly distinguished from the latter. The great pioneer in this area, Louis Pasteur, first and simply defined fermentation as life in the absence of oxygen. But today, a century after his pathbreaking work, fermentations are more precisely defined as those metabolic processes that occur in the dark and do not involve respiratory chains with either oxygen or nitrate as terminal electron acceptors. 

You can tiy working the other way, from the configurational label to the structure. Take lactic acid as an example. Lactic acid is produced by bacterial action on milk it s also produced in your muscles when they have to work with an insufficient supply of oxygen, such as during bursts of vigorous exercise. Lactic acid produced by fermentation is often racemic, though certain species of bacteria produce solely (R)-lactic acid. On the other hand, lactic acid produced by anaerobic respiration in muscles has the S configuration. 

Equations (1.3a) and (1.3b) illustrate the overall reactions of CO2 generation in aerobic and anaerobic respiration, respectively. Although not shown here, some types of bacterial fermentations can also be a source of CO2 for carbonate generation. Equation (1.5) explains the origin of C03 . This reaction is forced in the direction of C03 by loss of CO2 to the atmosphere in an open system, and by precipitation of calcium carbonate (CaC03), illustrated in Eq. (1.6), or by the formation of other carbonates not shown here. 

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