Biology Reference
In-Depth Information
phenomenon of
long-range correlations
, namely, the influence of molecules on the
behaviors of cells and multicellular systems exerted over distance scales varying by
10, time scales by 22, and volume ratios by 30 orders of magnitude as indicated in
the second, third, and fourth rows, respectively.
The spatiotemporal correlations over these scales may be expressed quantita-
tively in terms of “order parameter,” the concept borrowed from condensed matter
physics (Domb 1996), unique to living systems, which may be defined as the
degree
of correlation
(e.g.,
coincidence
or
synchrony
in the time dimension)
among critical
structures or events
(see the last row in Table
2.16
). In physics and chemistry, the
adjective, “critical,” refers to the value of a measurement, such as temperature,
pressure, or density, at which a physical system undergoes an abrupt change in
quality, property, or state. For example, at the
critical
temperature of 0
C, water
changes from the liquid (disordered) to solid (ordered) state, passing through the
critical state
or
phase
where both ordered and disordered states of water coexist.
The biological systems may exist in states resembling such a
critical state
, in that
ordered and nonordered processes can coexist in cells and multicellular systems.
It may be necessary to distinguish between two levels of order-disorder
transitions - at the molecular and organismic levels. At the molecular level,
biologists can employ the same opposite pairs,
order
vs.
disorder
, to describe,
say, protein structures, just as physicists use such an opposite pair to describe
physical states on either side of a critical point. At the organismic (i.e., cellular or
higher) levels, it may be necessary to adopt another opposite pair such as
life
vs.
nonlife
(or
live
vs.
dead)
. Thus, in biology, we may have a duality of opposite pairs:
(1)
order
vs.
disorder
on the molecular and subcellular levels, and (2)
life
vs.
nonlife
that is applicable to cells and multicellular systems.
It may well turn out that cells are constantly at a critical point in the sense that
both ordered and disordered states of subcellular constituents coexist as a means to
effectuate long-range interactions over micro- and meso-scopic scales, and such
interactions may be an essential condition for the
living state
of the cell (see Sect.
16.7
for a related discussion). If this view turns out to be correct, what is unique
about the phenomenon of life would be micro-macro correlation (e.g., the body
movement driven by molecular motors utilizing the free energy of ATP hydrolysis)
mediated by cells to couple micro- to meso-scale structures and processes. In this
sense, we may view cells as the effector or the agent of micro-macro correlations
(or coupling) under varied environmental conditions conducive to life, which
conditions may be referred to as “bio-critical points” (see Sect.
15.12
for a related
discussion).
Micro-meso correlations/interactions/couplings are evident in the theoretical
model of the cell known as the Bhopalator proposed in Ji (1985a). This model is
reproduced in Fig.
2.11
. The Bhopalator model appears to be the first comprehen-
sive molecular model of the living cell proposed in the literature. Two novel
concepts are embedded in the Bhopalator: (1) The ultimate form of the expression
of a gene is a dynamic structure called “dissipative structure” (or
dissipation
)
defined as any spatiotemporal distribution of matter produced and maintained by
