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of molecules, spatially concentrated and protected from external noises. In conclu-
sion, the following statement summarizes the biological cruciality of membranes.
Membranes built by phospholipids need water, and stable reactions need
membranes, therefore life, as we know it, needs water.
Fig. 1.1
The schema of a liposome (GNU Free Documentation License)
Fig. 1.2
Aggregation according to phospholipid bonds (top) and to phosphodiester bonds
(bottom)
Figure 1.2 shows the two fundamental kinds of biological aggregations. The one
at the top is typical of biological membranes. The one at bottom refers to DNA
molecules. Both aggregations are based on double links. But, in phospholipids
we have a
b
ilayer schema where firstly bilayer double monomers of type: (head-
tail)+(tail-head) are realized, and then these double monomers become elements
of aggregations along all directions (almost) parallel with the axis passing through
their heads. In this way, two surfaces, having heads externally, are in contact with
