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Typus
KomplettPlagiat
Bearbeiter
Klgn
Gesichtet
Yes.png
Untersuchte Arbeit:
Seite: 28, Zeilen: 1 ff. (entire page)
Quelle: Anézo 2003
Seite(n): 41, 42, Zeilen: 41:21 ff, 42:1 ff
[This chemical potential difference usually results from a difference in concentration (or activity) of the species on] one side versus the other. The solute diffuses down the concentration gradient, i.e. from a region of relatively high concentration to a region of relatively low concentration. Energy is obtained from the downhill flow – the amount of energy, also known as the free energy change ΔG, is directly proportional to the concentration difference. In the case of charged species, i.e. ions, an additional factor has to be taken into consideration. Indeed, many biological membranes are electrically positive on one side and negative on the other side, exhibiting a potential difference or voltage gradient across them. This arises from differences in the distribution of positive and negative ions on the two sides of the membranes. The diffusion of a charged species is considerably influenced by this transmembrane electrical potential. The inside of many cells is electrically negative compared with the outside: inward fluxes of positive ions and outward fluxes of negative ions are thus favored. For the transport of charged solutes, a concentration gradient as well as an electrical gradient have to be taken into account: both notions can be combined with the electrochemical gradient. The rate of diffusion of an uncharged species across a membrane is well described by Fick’s law:

J=P A \Delta C (1.1)

This states that the flux J, or amount of solute passing through the membrane per unit time, is directly proportional to the solute concentration gradient ΔC, to the area A of membrane absorptive surface, and depends on the permeability coefficient P of the solute in the membrane. The permeability coefficient is both characteristic of the solute and the membrane, and is defined as follows:

P=\frac{K D}{h} (1.2)

K is the partition coefficient of the diffusing species between the membrane and the aqueous phase and describes the relative solubility of the species in both media. D is the [diffusion coefficient of the solute in the membrane and represents the speed with which the solute can move through the membrane.]

[page 41]

This chemical potential difference usually results from a difference in concentration (or activity) of the species on one side versus the other. The solute diffuses down the concentration gradient, i.e. from a region of relatively high concentration to a region of relatively low concentration. Energy is obtained from the downhill flow; the amount of energy, also known as the free energy change ∆G, is directly proportional to the concentration difference. In the case of charged species, i.e. ions, an additional factor has to be taken into consideration. Indeed, many biological membranes are electrically positive on one side and negative on the other side, exhibiting a potential difference or voltage gradient across them. This arises from differences in the distribution of positive and negative ions on the two sides of the membranes. The diffusion of a charged species is considerably influenced by this transmembrane electrical potential. The inside of many cells is electrically negative compared with the outside: inward fluxes of positive ions and outward fluxes of negative ions are thus favored. For the transport of charged solutes, a concentration gradient as well as an electrical gradient

[page 42]

have to be taken into account: both notions can be combined with the electrochemical gradient. The rate of diffusion of an uncharged species across a membrane is well described by Fick’s law:

J=P \cdot A \cdot\Delta C (1.1)

This states that the flux J, or amount of solute passing through the membrane per unit time, is directly proportional to the solute concentration gradient ∆C, to the area A of membrane absorptive surface, and depends on the permeability coefficient P of the solute in the membrane. The permeability coefficient is both characteristic of the solute and the membrane, and is defined as follows:

P=\frac{K \cdot D}{h} (1.2)

K is the partition coefficient of the diffusing species between the membrane and the aqueous phase and describes the relative solubility of the species in both media. D is the diffusion coefficient of the solute in the membrane and represents the speed with which the solute can move through the membrane.

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(Klgn), WiseWoman

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