Biology Reference
In-Depth Information
like other features of the chemoton, will depend on specific stoichiometric rela-
tions. The sequential order, however, will not-it is a 'free' property which can
then be linked to component operations in the chemoton in other ways so as
to control them. Moreover, it can also undergo selection. This indicates to a
general point about control systems-if control is to involve more than strict
linkage between components, what is required is a property in the system that
varies independently of the basic operations. Particular values of this variable
property can then be coordinated with responses by other components so that
the property can exert control over the operation of the other component.
What is required for an information-based control system that goes beyond
direct negative feedback loops, then, is a property that is sufficiently indepen-
dent of the processes of material and energy flow such that it can be varied
without disrupting these basic processes (which may themselves be maintained
by negative feedback), but still be able to be linked to parts of the mechanism
to enable the modulation of their operations. Such properties need not involve
a template matching system but there are reasons to employ such a system. We
can appreciate this by considering the role of enzymes in catabolism. On some
occasions
23
Gánti tries to characterize the chemoton without invoking catalysts
or enzymes to promote the reactions, but it is ultimately unlikely that a system of
uncatalyzed reactions could maintain the flow of matter and energy needed in the
chemoton. If enzymes are to play a role, however, they must be synthesized by
the system. The method for synthesizing proteins, including enzymes, in actual
living cells utilizes a common mechanism (a ribosome) that adds amino acids to
a developing string. If this mechanism is to produce different enzymes on differ-
ent occasions (as it must if the result is the set of proteins needed to catalyze a
given reaction), a stable information source for specifying the sequence in each
protein is required (plus a component for insuring that the right instructions are
followed at a given time). In living cells, mRNA plays this role. Here we see
a compelling reason for an informational system - it insures that the system is
able to make the needed components so that it is able to function. The fact that
it also provides the retention component for a process involving variation and
selective retention, i.e., natural selection (Lewontin, 1970), is an added plus but
not an essential feature of the information-based control system.
Gánti's chemoton proposal is highly speculative, but it offers an intriguing
perspective on the centrality of cyclic organization in biological systems. Cycles
provide a vehicle through which a set of operations that depend on each other
can be maintained even as the overall mechanism performs work. When part of
23
When he appeals to examples such as the Krebs' cycle, however, Gánti is already invoking an enzyme-
catalyzed metabolic cycle. Enzyme-catalyzed systems pose an additional challenge for Gánti's account as they
must themselves be made by the system. One way to view this is to differentiate the function of procuring
raw materials and energy from that of synthesizing new products, and distinguishing both of these from the
functions of differentiating the system from its environment and of storing information in a template.
