Membrane transport single-site

For a vapor-equilibrated membrane (i.e., one that is in contact with water vapor only), the physical model proposes that there is water in the ionic domains but none in the collapsed channels except for the bound water hydrating the few sulfonic acid sites present. Furthermore, the sulfonic acid sites that make up the collapsed channels are always fluctuating, but the elusters are elose enough together to form a transport pathway after the pereolation threshold has been reached. Due to the nature of the collapsed ehaimels, the membrane is treated as a homogenous single-phase system. In this sense, the water vapor does not penetrate into the cluster-network, but instead dissolves into the membrane. Thus, the vapor-equilibrated membrane transport mechanism is similar to the single-phase transport models mentioned previously. 

Kang, Y. S., Hong, J., Jang, J., and Kim, U. Y. (1996). Analysis of faciUtated transport in soUd membranes with fixed site carriers 1. Single RC circuit model. J. Membr. Sci. 109, 149. 

The processes of electron transport and oxidative phosphorylation are membrane-associated. Bacteria are the simplest life form, and bacterial cells typically consist of a single cellular compartment surrounded by a plasma membrane and a more rigid cell wall. In such a system, the conversion of energy from NADH and [FADHg] to the energy of ATP via electron transport and oxidative phosphorylation is carried out at (and across) the plasma membrane. In eukaryotic cells, electron transport and oxidative phosphorylation are localized in mitochondria, which are also the sites of TCA cycle activity and (as we shall see in Chapter 24) fatty acid oxidation. Mammalian cells contain from 800 to 2500 mitochondria other types of cells may have as few as one or two or as many as half a million mitochondria. Human erythrocytes, whose purpose is simply to transport oxygen to tissues, contain no mitochondria at all. The typical mitochondrion is about 0.5 0.3 microns in diameter and from 0.5 micron to several microns long its overall shape is sensitive to metabolic conditions in the cell. 

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