Physics - Molecular Theory of the Living Cell - page 7

Equilibrium structures such as atoms can exist in two states - ground state and
excited state , and the transitions between them require absorbing or emitting/
releasing energy as in electronic transitions of atoms giving rise to atomic line
spectra (see Fig. 10.5 b) (Moore 1963). Nonequilibrium structures divide into two
classes - near-equilibrium systems obeying the Onsager reciprocity relation
(Prigogine 1980, pp. 84-90) and far-from-equilibrium systems exhibiting nonlinear
behaviors such as amplification, self-organization, metastability (Kelso 1995; Kelso
and Engstrøm 2006), and deterministic chaos (Domb 1996; Prigogine 1980,
pp. 103-150). Although chemical reaction-diffusion systems have been claimed to
require far-from-equilibrium conditions in order to exhibit self-organization
(Prigogine 1980, pp. 103-150), we cannot exclude the possibility that enzyme-
catalyzed chemical reaction-diffusion systems can self-organize in space and time
even at near-equilibrium in living systems due to the nonlinear behaviors inherent in
enzymes themselves . If this conjecture proves to be true, the far-from-equilibrium
condition of Prigogine may not be universally necessary for biological
organizations. Dissipative structures such as cells can exist in two states - “resting,”
and “activated” or “energized.” Examples of resting dissipative structures include
quiescent immune cells such as Kupffer cells in the liver (Laskin 2009; Laskin et al.
2010) and quiescent neurons, and the examples of activated dissipative structures are
exemplified by immune cells activated by cytokines (Laskin et al. 2010) and neurons
exhibiting function-related firing patterns triggered by neurotransmitters.
2.1.2 Free Energy vs. Thermal Energy in Enzymic Catalysis
Thermal fluctuations (also called Brownian motions ) are essential for life (see
Sects. 11.3.3 and 12.12 ). According to the conformon theory of enzymic catalysis
(Ji 1974a, b, 2000), (1) enzymes require thermal fluctuations for their activities,
(2) thermal fluctuations of enzymes require heat, and hence (3) enzymes need heat
to function. Despite their obvious importance, the thermal motions and thermal
energies are often viewed by biologists as irrelevant or even harmful to living
processes on the molecular level.
It is important to distinguish between two kinds of energy - free energy and
thermal energy . Free energy (e.g., Gibbs free energy, G) is a useful form of energy ,
being a function of both energy (E) and entropy (S) (Kondepudi and Prigogine 1998;
Kondepudi 2008; Moore 1963) as already indicated (see Eq. 2.1 ), whereas thermal
energy cannot be utilized to do any useful work without temperature gradient. Life
depends on free energy which is needed to “pump up” living systems. To use thermal
energy without temperature gradient is tantamount to violating the Second Law of
thermodynamics. This is probably why biologists have been reluctant to implicate
any thermal energy in living processes (which mostly occur under homeothermic
conditions , i.e., without any temperature gradient). But, according to the conformon
theory of enzymic catalysis, thermal energy can be utilized by enzymes “transiently”
without violating the Second Law, even in the absence of any sustained temperature