Page 111 - Visions of the Future Chemistry and Life Science

100 A. R. HEMSLEY AND P. C. GRIFFITHS

contained within DNA. The nature of proteins is such that a single base
change in the genetic sequence can code for a different amino acid which,
in turn can give rise to a different molecular configuration. A different
protein within a construction sequence will have no effect (possibly by
coding for the same amino acid), cause it to fail, or occasionally cause it to
produce something different that does something useful within the organ-
ism. The nature of such mechanisms is essentially chaotic in that they
exhibit both robustness and fragility. The substitution of many amino
acids within a protein need not significantly change its folding pattern if
these are chosen with care with respect to the influence they have on
folding (robustness). However, the substitution of any one critical amino
acid will cause the adoption of a different configuration (fragility).
Alongside such potential generators of robust difference are so-called
‘antichaotic’ factors as proposed by Kauffman. In antichaotic systems, the
great complexity of components within the cellular soup are seen to be
fully interactive with each other. These systems can be perturbed, but are
in a sense self-generating and in a state of balance. Such systems act to
maintain this equilibrium but if distorted to excess, will ‘snap’ to an alter-
native stable state.
It is against this background that we have been investigating the struc-
ture and development of spores from the club moss Selaginella. These
show complex microscopic architecture within their relatively thick walls
(Figure 6.1(c)). The presence of an apparently colloidal crystal region within
the wall, which consists of more or less spherical particles of sporopolle-
nin, has been determined. This has focused attention on constructional
mechanisms involving processes of colloidal interaction in order to
account for the crystalline region and the other structures encountered
within the complex walls. It has become apparent that a full understand-
ing of this mode of microarchitectural construction lies as much with an
appreciation of colloid and surfactant interactions as it does with ‘biologi-
cal’ control mechanisms.

6.2 Consideration of colloidal interactions and self-assembly
6.2.1 The unexpected behaviour of tiny objects
Whilst our understanding of the relevant factors important to colloid
science in terms of synthetic applications and materials (e.g. paints) is
quite advanced, as we have seen the same cannot be said for the ‘colloid