... of more interest The basic constituents of all membranes are phospholipids, although there are different types of lipid present that I shall discuss later. All these molecules are amphipathic and therefore they have a polar 'head' and a hydrophobic 'tail'. They are based on the glycerol molecule, a triol, which uses one of its slightly polarised -OH groups to bind to a phosphate group. Then, two fatty acid chains are attached to the other two hydroxyl groups on the glycerol. The fatty acid chains consist of a hydrocarbon chain of 16-20 carbons although the one bound to the middle hydroxyl group often has a cis double bond which makes it bend slightly away from the other chain. [diag.alberts,p.277, 6-2(b)without choline] This is a curious process in the sense that hydrophobic molecules are being bound to another with a polar phosphate group. This reaction would seem energetically very unfavourable, yet it ...

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