Anaerobic fermentation products respiration

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). 

In true fermentation, the free energy drop between substrate (say glucose) and anaerobic end products is always modest by comparison with respiration, because fermentation is never based on electron transfer chains coupled to phosphorylation. Rather, true fermentations depend upon a variety of oxidation-reduction reactions involving organic compounds, C02, molecular hydrogen, or sulfur compounds. All these reactions are inefficient in terms of energy yield (moles ATP per mole substrate fermented), and, therefore, the mass of cells obtainable per mole of substrate is much smaller than with respiratory-dependent species. 

GA3P is subsequently converted, in a number of steps, into pyruvate (PYR), which is the branch-point between fermentation and respiration. Saccharomyces species are particularly well adapted to the anaerobic production of ethanol, via decarboxylation and reduction of PYR, to the near-exclusion of other metabolites. On account of this latter characteristic, as well as its high ethanol tolerance, Saccharomyces is the preferred organism to produce ethanol from hexoses. 

Brief attention has been directed in Chapter 4, Section 4.3.4 to anaerobic bacteria that are important in the decarboxylation of dicarboxylic acids including oxalate and malonate—and succinate that is produced as a fermentation product of carbohydrates, and in anaerobic respirations involving fumarate. The various anaerobic organisms, and their metabolic capabilities are briefly summarized here ... 

Fenton reaction reaction of iron with hydrogen peroxide to form hydroxyl radicals, fermentation form of anaerobic (oxygen-free) respiration used by yeasts, which produces ethanol as an end-product, ferritin cage-like protein that locks away iron within cells. 

The production of ATP is achieved by glucose, pyruvate, and NADH oxidation in the presence of oxygen (aerobic respiration). In the absence or in the presence of limited amounts of oxygen, the glycolytic products will be metabolized by anaerobic fermentation using alternative substrates such as nitrite. ... 

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. 

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. 

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