Chemistry - Molecular Theory of the Living Cell - page 71

The concepts of dissipative structures or self-organizing chemical reaction--
diffusion systems are not confined to abiotic (or inanimate) systems, but can be
extended to biotic (or animate) systems such as intracellular chemical reaction--
diffusion processes, which were first demonstrated experimentally in chemotaxing
human neutrophils by Sawyer, Sullivan, and Mendel (1985) (see Fig. 3.2 ). What is
interesting about the findings of these investigators is that the direction of the
intracellular calcium ion gradient determines the direction of the chemotactic
movement of the cell as a whole. This is one of the first examples of intracellular
dissipative structures (IDSs), that is, intracellular calcium gradients, in this case,
that are observed to be linked to cell functions . Figure 3.2 offers two important take-
home messages - (1) dissipative structures in the form of ion gradients can be
generated inside a cell without any membranes (see Panels F, I, and L), and (2) IDSs
determine cell functions.
There are three major differences to be noted between the dissipative structures
in the Belousov-Zhabotinsky (BZ) reaction shown in Fig. 3.1 and the dissipative
structures shown in Fig. 3.2 : (1) The boundary (i.e., the reaction vessel wall) of the
BZ reaction is fixed, and (2) The boundary of IDSs (such as the intracellular
calcium ion gradients) is mobile, and (3) The BZ reaction is a purely chemical
reaction-diffusion system, while the intracellular dissipative structures in Fig. 3.2
are chemical reactions catalyzed by enzymes which encode genetic information.
Hence, the cell can be viewed as dissipative structure regulated by genetic informa-
tion or as a “genetically informed dissipatons (GIDs).”
3.1.3 Pericellular Ion Gradients and Action Potentials
The action potential is another example of dissipative structures with a well-defined
biological function, for example, the transmission of information along the axon.
Action potentials (APs) differ from intracellular calcium ion gradients as shown
in Fig. 3.2 , in that they implicate a movement of ions across the cell membrane.
For this reason, it may be more accurate to refer to action potentials as “transmem-
brane” or “pericellular dissipative structures” (TDSs or PDSs) in contrast to cyto-
solic calcium ion gradients which are “intracellular dissipative structures” (IDSs).
APs can be viewed as a network of transmembrane transport processes of four key
ions, namely, K + ,Na + ,Ca ++ , and Cl that are precisely coordinated in time and
space with respect to the direction and speed of ion movements.
According to the Bhopalator model of the cell (Ji 1985a, b, 2002b), the final form
of gene expression is not proteins as is widely believed but a set of intracellular
dissipative structures (IDSs) or dissipatons , including transmembrane dissipative
structures and mechanical stress gradients of the cytoskeleton (Ingber 1998;
Chicurel et al. 1998). Since IDSs and cell functions are determined by genes to a