![]() ![]() Intriguingly, it was found that persisters could be derived from the fastest-growing bacterial subpopulation, and that dormancy is neither necessary nor sufficient for the formation of persisters 4, 6. 5 showed that starvation-induced antibiotic tolerance involves curtailing the production of pro-oxidant metabolites and increasing antioxidant defenses. Recent studies suggest the existence of redundant cellular mechanisms underlying tolerance formation and that dormancy alone is insufficient for long-term maintenance of the tolerance phenotype 4. Hence, delineating the cellular mechanisms that underlie the onset and long-term maintenance of a stable antibiotic tolerance phenotype in bacteria is more clinically relevant than studying mechanisms governing the emergence of transient antibiotic tolerance in an exponentially growing population. Recent studies reveal that the re-growth of antibiotic-tolerant cells, commonly known as persisters, that reside in the human body for a prolonged period is responsible for causing a wide range of chronic and recurrent infections, especially among immuno-compromised patients 2, 3. The cell lacks genes encoding an appropriate cytochrome oxidase for transferring electrons to oxygen at the end of the electron transport system.Bacterial antibiotic tolerance is loosely defined as the ability to withstand the deleterious effects of antibiotics at concentrations that can otherwise be lethal, without exhibiting a change in antibiotic susceptibility upon re-growth under favorable conditions 1.There are many circumstances under which aerobic respiration is not possible, including any one or more of the following: coli, are negative for this test because they produce different cytochrome oxidase types. For example, the gram-negative opportunist Pseudomonas aeruginosa and the gram-negative cholera-causing Vibrio cholerae use cytochrome c oxidase, which can be detected by the oxidase test, whereas other gram-negative Enterobacteriaceae, like E. This electron carrier, cytochrome oxidase, differs between bacterial types and can be used to differentiate closely related bacteria for diagnoses. In aerobic respiration, the final electron acceptor (i.e., the one having the most positive redox potential) at the end of the ETS is an oxygen molecule (O 2) that becomes reduced to water (H 2O) by the final ETS carrier. The four major classes of electron carriers involved in both eukaryotic and prokaryotic electron transport systems are the cytochromes, flavoproteins, iron-sulfur proteins, and the quinones. Therefore, electrons move from electron carriers with more negative redox potential to those with more positive redox potential. For a protein or chemical to accept electrons, it must have a more positive redox potential than the electron donor. These carriers can pass electrons along in the ETS because of their redox potential. Electron transport is a series of chemical reactions that resembles a bucket brigade in that electrons from NADH and FADH 2 are passed rapidly from one ETS electron carrier to the next. The electron transport system (ETS) is the last component involved in the process of cellular respiration it comprises a series of membrane-associated protein complexes and associated mobile accessory electron carriers. The energy of the electrons is harvested to generate an electrochemical gradient across the membrane, which is used to make ATP by oxidative phosphorylation. These electron transfers take place on the inner part of the cell membrane of prokaryotic cells or in specialized protein complexes in the inner membrane of the mitochondria of eukaryotic cells. ![]() Cellular respiration begins when electrons are transferred from NADH and FADH 2-made in glycolysis, the transition reaction, and the Krebs cycle-through a series of chemical reactions to a final inorganic electron acceptor (either oxygen in aerobic respiration or non-oxygen inorganic molecules in anaerobic respiration). Most ATP, however, is generated during a separate process called oxidative phosphorylation, which occurs during cellular respiration. We have just discussed two pathways in glucose catabolism-glycolysis and the Krebs cycle-that generate ATP by substrate-level phosphorylation. Compare and contrast aerobic and anaerobic respiration.Describe the function and location of ATP synthase in a prokaryotic versus eukaryotic cell.Explain the relationship between chemiosmosis and proton motive force.Compare and contrast the differences between substrate-level and oxidative phosphorylation.Compare and contrast the electron transport system location and function in a prokaryotic cell and a eukaryotic cell. ![]()
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