Glycolysis, anaerobic Embden-Meyerhof pathway

The major pathway by which glucose is metabohsed to give energy has two stages. The first, known as glycolysis, can occur under anaerobic conditions and results in the production of pyruvate. The sequence of reactions (Fig. 9.4), often referred to as the Embden-Meyerhof pathway, takes place in the cell cytoplasm. 

In general, carbohydrates are broken down aerobically, i.e. with a supply of oxygen. Anaerobic glycolysis seems to be more of a bypass for cells with a poor oxygen supply. The Embden-Meyerhof pathway is significant primarily because it operates not only under anaerobic conditions but, up to the step of pyruvate, under aerobic conditions as well (at least to the extent that glucose is not oxidized directly to pentose (Section 6, Chapt. XVIlI-1). Reduced nicotinamide-adenine dinucleotide is reoxidized through the respiratory chain, and pyruvate can be metabolized further in a variety of ways. 

During anaerobic glycolysis a lot of lactate is produced, and it has been known for some time that part of this lactate is used for the resynthesis of glucose, though not in the muscle, the place of its origin, but rather in the liver. In theory, the synthesis might be a simple reversal of the Embden-Meyerhof pathway, but the equilibria of some of the reactions are too unfavorable. This is true particularly of the reaction of pyruvate kinase the phosphorylation of pyruvate by this reaction would require very high concentrations of ATP. 

The Pasteur Effect. It is an old observation that cells, e.g. of muscle or yeast, transform much glucose (to lactate or ethanol) imder anaerobic conditions. If oxygen is supplied, however, then not only is anaerobic glycolysis inhibited, but much less glucose actually enters the Embden-Meyerhof pathway. Evidently, the oxidative processes of mitochondria exert some influence back on the cytoplasm. This seems rather sensible physiologically, since in aerobiosis a great quantity of ATP is produced in the respiratory chain and the demands for energy can w ell be met with less substrate. However, this does not explain the mechanism responsible for the effect, which is known as the Pasteur effect. ... 

Glycolysis, also called as Embden-Meyerhof-Pamas pathway (EMP pathway). Glycolysis is of central importance to the metabolism of eukaryotic cells. It links the metabolism of sugars to that of organic acids in the Krebs cycle, and in anaerobic organisms, provides the principle route of energy (ATP) generation. The reactions are rather complex, but can be seen as four basic processes (Fig. 9.2) ... 

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