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Fig. 8.9
The conformon hypothesis of coupled processes in the cell
they are not predictable. In order for the cell to carry out its functions such as growth,
chemotaxis, cell cycle, cell differentiation, and apoptosis (i.e., programed cell death)
in interaction with its environment through its various receptors (both membrane-
bound and cytosolic), many up-hill reactions must be carried out (driven by conju-
gate down-hill reactions resulting in nonrandom motions) in thermally fluctuating
environment without violating the laws of thermodynamics. Such coupled processes
are often referred to as “energy-coupled” processes, meaning that the free energy
released from the down-hill reaction is partially “transferred” to the coupled up-hill
reaction in such a manner that the net free energy change accompanying the overall
process remains negative. Examples of energy-coupled processes include respira-
tion-driven ATP synthesis (i.e.,
oxidative phosphorylation
), ATP- or respiration-
driven active transport of protons across the mitochondrial inner membrane, and
ATP-driven molecular motors and rotors, and the formation and destruction of
molecular machines (Green and Ji 1972a, b; Ji 1974b, 2000) maintains that all
such coupled processes proceed through the production and consumption of
conformons
(the mechanical energy stored in sequence-specific sites within
biopolymers that acts as force generator). This idea can be represented schematically
as shown in Fig.
8.9
.
The coupled processes include (1) oxidative phosphorylation, (2) active trans-
port, (3) muscle contraction, (4) intracellular molecular trafficking, (5) signal
transduction, (6) gene expression, (7) DNA repair, (8) cell cycle, (9) space- and
time-dependent production and destruction of hyperstructures or SOWAWN
machines, (10) intercellular communication, (11) cell migration, and (12) cell
shape changes.
When the mechanistic scheme shown in Fig.
8.9
is applied to mitochondria
which carry out at least two coupled processes, namely, respiration-driven ATP
synthesis (i.e., oxidative phosphorylation) and respiration-driven proton extrusion,
we can construct the following scheme:
As will be discussed in Sect.
11.6
, the chemiosmotic hypothesis of P. Mitchell
(1961, 1968) assumes that respiration directly generates the proton gradient across
the mitochondrial inner membrane, which subsequently drives the synthesis of ATP
from ADP and Pi. In contrast, the conformon hypothesis, shown in Fig.
8.10
,
assumes that respiration first produce conformons (via the detailed mechanism
discussed in Sects.
8.2
and
11.5
), which then drives either the synthesis of ATP
from ADP and Pi or the extrusion of protons from the matrix to the cytosolic space.
Since the chemiosmotic mechanism absolutely depends on the presence of
biomembrane, it cannot mediate the coupling of nonmembrane-dependent pro-
cesses such as gene expression, muscle contraction, and molecular trafficking in
the cytosol. Of the 12 coupled processes cited above that can be driven by
