Physics - Molecular Theory of the Living Cell - page 57

1994; Huggett and Weingard 1995; Domb 1996; Fisher 1998; Stanley 1999), and
the language of networks that has emerged in recent years as a powerful new tool in
science (Barabasi 2002).
Renormalizable networks as defined above are synonymous with S elf- O rganizing-
W henever- A nd- W herever- N eeded (SOWAWN) machines (Ji 2006b, 2007b). The
concept of machines (or systems) is indispensable in understanding living structures
and processes at all levels of organization - from molecules, to cells, to the blood
coagulation cascade, to the human body, and to societies. One of the reasons for the
universal usefulness of the machine concept in living systems appears to be the
possibility of applying to biosystems the Law of Requisite Variety (LRV; see Sect.
5.3.2 ), which provides the principles underlying the complexity of the internal
structures of machines or systems.
In the course of teaching Theoretical Aspects of Pharmacology to Pharm D
students at Rutgers University in 2005, it occurred to me that there may be a new
kind of machine operating in cells and the human body, which the author elected to
call “self-organizing-whenever-and-wherever-needed” (SOWAWN) machine, for
the lack of a better term. The idea of SOWAWN (pronounced “sow-on”) machine
came as I was discussing the blood coagulation system with students, one of the
most complicated biochemical, biophysical, and cellular processes that go on in our
body. At least a dozen proteins (called blood coagulation factors) and two cell types
(platelets and red blood cells) and several biochemical entities (e.g., thromboxane)
participate in a dynamic process triggered by signals released from ruptured blood
vessels whose purpose is to stop bleeding by forming insoluble clots around the
damaged vessel (and not anywhere else). The blood coagulation cascade is a good
example of SOWAWN machines, because:
1. It is activated (or assembled) only when and where needed in order to prevent
interfering with normal blood flow in body compartments without any damaged
vessels.
2. It does not exist pre-assembled, because any pre-assembled components of the
blood cascade system may plug up capillaries due to their bulky molecular
dimensions.
3. The necessary components of the blood coagulation cascade are randomly
distributed in the blood compartment and are constantly available anywhere in
our vascular system so that they can be signaled to carry out pre-programmed
actions at moment's notice.
4. The free energy needed to drive the self-assembling processes may be derived
from the hydrolysis of proteins which provides about ¼ of the Gibbs free energy
of ATP hydrolysis (In other words, peptide bonds may serve as the extracellular
analogs of ATP).
Another example of SOWAWN machines is the so-called signal transduction
cascades or pathways inside the cell. A signal transduction pathway (comprising,
again, about a dozen proteins) in cells are activated by signals (e.g., hormones)
binding to cell membrane receptors (Table 12.14 and Fig. 12.34 ). A signal-bound
cell membrane receptor undergoes a shape (or conformational) change which