permeability of membranes

permeability of membranes

a theoretical concept of the permeability of a cell membrane, in which the membrane structure is thought to contain pores through which solutes can sometimes pass down a CONCENTRATION GRADIENT by DIFFUSION (see FLUID-MOSAIC MODEL). Many membranes are, however, differentially permeable to certain molecules. For example, SELECTIVE PERMEABILITY enables OSMOSIS to take place. Others will allow movement against a concentration gradient by ACTIVE TRANSPORT. An example is the removal of sodium by cells surrounded by a higher sodium concentration.
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As exhibited in Figure 7 and Table 1, the permeability of membranes N-117/ Si[O.sub.2]- S[O.sub.3]H, NM-0.5H, NM-1H, and NM-24H is 3.13 x [10.sup.-6] [cm.sup.2]/min, 0.2 x [10.sup.-6] [cm.sup.2]/min, 0.13 x [10.sup.-6] [cm.sup.2]/min, and 0.12 x [10.sup.-6] [cm.sup.2]/min, respectively.
The time-lag method is a powerful and yet simple method to characterize permeation processes and it is used to determine the permeability of membranes toward gases and solutes.
The water vapour permeability of membranes was determined using (Water Vapor Permeability, Macon, Model 3/61.
Insertion of cholesterol into plasma membrane is an essential component of eukaryote plasma membranes; it affects membrane fluidity and reduces the permeability of membranes (2).
8, the crosslinking density effect on the methanol permeability of membranes prepared is shown.
The so-called time-lag method is commonly used to obtain the permeability of membranes. (5,6) A concentration step perturbation is performed in one chamber of a two-chamber permeation cell, which is divided by the membrane, and the response followed by analyzing the concentration at the other chamber.