Page 121 - Visions of the Future Chemistry and Life Science

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

in a single base pair and thus produce similar concentrations of compo-
nents) but because this gives rise to initiation points either side of a domain
boundary, the resulting structure is different, possibly very different
(strings or laminae). Points c and c , although probably closer to each other
(genetically) than a and a , may be considered to exhibit the greatest differ-
ence in microarchitectural expression since these are separated by two
domain boundaries. Significantly, it may not matter for any subsequent
stage of development from where within each domain, the original compo-
sition was positioned since what matters is how the new components
interact to initiate the next stage of development. It is abundantly clear
from this illustration, that assessment of relationships of organisms based
on comparison of the genetic code would differ somewhat from any assess-
ment of based on patterning and structure. Consider the likely outcome of
such an analysis on a, a , c and c There are further complications in that
composition will usually change as wall development occurs (consider
arrow from d to d and compare with Figure 6.1(c), development is from
bottom to top). In addition, any in vivo self-assembly system such as this
is reliant upon second hand manipulation by proteins/enzymes which
have already been through a similar selection process.
The incorporation of self-assembly mechanisms in development is
clearly advantageous to an organism if the processes involved are suffi-
ciently robust and the results consistent. Such systems represent a saving
in terms of both the required genetic code and its decryption (via riboso-
mal RNA) into enzymic regulatory proteins. The genetic code need only
describe the initial conditions and not the complexity of the ultimate
structure. Over the great expanse of time involved in the evolution of life
(particularly simple, single-celled organisms) many self-assembly mecha-
nisms have been included by chance, much as proteins with a specific func-
tion have been retained and elaborated. Amongst organisms, many
self-assembly mechanisms are shared (although they may result in differ-
ent patterns and architecture due to different initial conditions), whilst
others may be unique. However, the identification of such mechanisms
and an assessment of their distribution amongst organisms will surely
assist in both an understanding of organismal relationships and the
meaning of structural, architectural and pattern diversity between
‘species’. The observation that self-assembly systems can switch from the
production of one pattern to another with only minor modification of the
initial conditions (supported by our colloidal work) adds weight to the view