Membrane structures dissipative

FIGURE 21.31 Structures of several uiicouplers, molecules that dissipate the proton gradient across the inner mitochondrial membrane and thereby destroy the tight coupling between electron transport and the ATP synthase reaction. 

Although these systems involve two variables, their steady-state solutions can be calculated in general and a more complete mathematical analysis of dissipative structures is possible. From a practical point of view it is interesting to note that systems obeying equations of the form (2) may be found in artificial membrane reactors.22 Examples are presented by D. Thomas in this volume. 

B. Hess, A. Boiteux, H. G. Busse, and G. Gerisch, in Membranes, Dissipative Structures, and Evolution, G. Nicolis and R. Lefever, Eds., Interscience-Wiley New York, pp. 

Examination of its structure shows why the cell is the fundamental unit of life. The defining feature of a cell is a membrane—a chemical structure that divides the outside world from the interior of the cell. With the protection of a membrane, a cell can maintain different conditions inside than prevails outside. For example cells can concentrate nutrients in their interior so that they are available for energy production and can prevent newly made structural materials from being washed away. In the absence of a membrane, the large array of metabolic reactions necessary to sustain life would quickly dissipate. 

Much as liquid water is essential for life, frozen water, ice, is frequently lethal, especially if ice formation occurs within the cell. Upon formation of ice, loss of liquid water may impair or preclude the four basic water-related functions listed above. In particular, the structures and the activities of macromolecules and membranes may be severely damaged. In fact, the harmful effects of ice formation are due to a suite of physical and chemical effects. Physical damage from ice crystals that form within a cell can lead to rupture of membranes and the consequent dissipation of concentration gradients between the cell and external fluids or between membrane-bounded compartments within the cell. Ice formation in the extracellular fluids also can lead to damage to membranes as well as to lethal dehydration of the cell, as water moves down its concentration gradient from the intracellular space to the now depleted pool of liquid water in the extracellular space. Dehydration of the cell not only deprives it of water, but also leads to harmful and perhaps lethal increases in the concentrations of inorganic ions, which remain behind in the cell. Because the activities and structures of nucleic acids and proteins are affected by the concentrations of ions in their milieu, dehydration is expected to lead to perturbation of macromolecular structure and metabolic activity. It should come as no surprise, therefore, that with rare exceptions such as the fat body cells of certain cold-tolerant insects (Lee et al., 1993b Salt, 1962), ice formation within cells is lethal. 

Nisin is the best-characterized LAB bacteriocin. The structure of nisin was first elucidated by Gross and Morell (1971). Nisin dissipates the membrane potential in cells of sensitive organisms (Ruhr and Sahl, 1985) and causes PMF depletion of whole cells of L. monocytogenes (Bruno et al.,... 

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