Figure 2-12 Overview diagram of the central metabolic pathways (Embden-Meyerhof-Pamas [EMP], the tricarboxylic acid [TCA] cycle, and the pentose phosphate shunt). Precursor metabolites (see also Figure 2-11) that are produced are highlighted in red; production of energy in the form of ATP (-P) by substrate-level phosphorylation is highlighted in yellow, and reduced carrier molecules for transport of electrons used in oxidative phosphorylation are highlighted in green. (Modified from Niedhardt FC, Ingraham JL, Schaechter M, editors: Physiology of the bacterial cell: a molecular approach, Sunderland, Mass, 1990, Sinauer Associates.)
for laboratory identification of bacteria (see Chapter 7 for more information on the biochemical basis for bacterial identification).
Oxidative phosphorylation involves an electron transport system that conducts a series of electron transfers from reduced carrier molecules such as NADH2 and NADPH2, produced in the ¿entrai pathways (see Figure 2-12), to a terminal electron acceptor. The energy produced by the series of oxidation-reduction reactions is used to generate ATP from ADP. When oxidative phosphorylation uses oxygen as the terminal electron acceptor, the process is known as aerobic respiration. Anaerobic respiration refers to processes that use final electron acceptors other than oxygen.
Knowledge regarding which mechanisms bacteria use to generate ATP is important for designing laboratory protocols for cultivating and identifying these organisms. For example, some bacteria solely depend on aerobic respiration and cannot grow in the absence of oxygen (strictly aerobic bacteria). Others can use either aerobic respiration or fermentation, depending on the availability of oxygen (facultatively anaerobic bacteria). For still others, oxygen is absolutely toxic (strictly anaerobic bacteria).
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