<P> Non-electrolytes, substances that generally are hydrophobic and lipophylic, usually pass through the membrane by dissolution in the lipid bilayer, and therefore, by passive diffusion . For those non-electrolytes whose transport through the membrane is mediated by a transport protein the ability to diffuse is, generally, dependent on the partition coefficient K. Partially charged non-electrolytes, that are more or less polar, such as ethanol, methanol or urea, are able to pass through the membrane through aqueous channels immersed in the membrane . It is interesting to note that there is no effective regulation mechanism that limits this transport, which indicates an intrinsic vulnerability of the cells to the penetration of these molecules . </P> <P> There are several databases which attempt to construct phylogenetic trees detailing the creation of transporter proteins . One such resource is the Transporter Classification database </P>

Which is not a characteristic of mediated transport