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control over the overall flux through the full system, but completely determines
the degree of homeostasis of M. However, this can only happen if enzyme
1 retains flux control over that part of the system that leads up to M (the supply
pathway for M). As before this is partly determined by the ratio p/K
p
, which
must be small. When K
p
becomes smaller and p/K
p
increases concomitantly, the
system becomes structurally unstable and exhibits multistationarity (Hofmeyr et
al., 2000). This behaviour only obtains when enzyme 1 binds S and P coop-
eratively, which is the norm for allosteric enzymes, and it is independent of
the specific mechanism (Hofmeyr & Cornish-Bowden, 1997). It is therefore
conceivable that evolution has selected for large values of K
p
in order to avoid
this type of pathological behaviour. However, most kinetic studies of allosteric
enzymes have ignored the K
p
and it may turn out that in some cases K
p
is small,
which could cause the system to exhibit switching behaviour instead of a smooth
response to changes in the concentration of M. Whatever the case may be, it is
clear that one can only understand why K
p
has the value that it has by analysing
it in its functional context, which need not be that of the whole cell. Having now
made and illustrated the claim that nothing in an organism makes sense except
in the light of context, it is time to consider the nature of the overall context that
the living cell provides for systems biology. This amounts to asking of systems
biology how it defines life.
2. THE SELF-FABRICATING CELL: A CONTEXT FOR SYSTEMS
BIOLOGY
Ironically, biology itself provides a ground upon which epistemology and ontology
directly meet. Put simply, organisms are themselves fabricators; they build new
things, they make new things, they deploy new things. Hence, an essential part
of a theory of organism is precisely a theory of fabrication; a theory of invention
and deployment. Thus, a theory of organisms has within itself an ineluctable
ontological component; a science of fabrication. Nothing shows more clearly than
this the unique character of biology among the sciences, and the unique role that
its own theory must play in its own application.
(Robert Rosen,
On Theory in Biology
3
)
Biologists, more than ever before, are living in a golden age. The cell, that
unit on which all life is based, no longer seems a mystery; in fact, we apparently
feel we know and understand it so well and have such advanced technology
that we can manipulate life at the molecular level confidently and responsibly.
However, keeping in mind E.F. Schumacher's admonition that 'the greatest
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