Biology Reference
In-Depth Information
pp. 228-231; Harris 1993, pp. 57-58, 99-100). A molecular version of RGC may
be stated as follows:
Just as humans can produce an indefinitely large number of novel and meaningful sentences
based on finite sets of words and grammatical rules, so living cells have evolved to produce
an indefinitely large number of novel (i.e., unpredictable) functional molecular processes
based on finite sets of molecules and physicochemical principles. (6.18)
Statement 6.18 may be referred to as the principle of rule-governed productivity,
the principle of constrained freedom (PCF), or the principle of rule-governed
molecular creativity. The principle of constrained freedom is symmetric or isomor-
phic with the principle of rule-governed creativity with respect to the following
transformations.
1. Replacing “rule-governed” with “constrained”
2. Replacing “creativity” with “freedom”
These mutually replaceable elements in quotation marks may be considered to
form a group comparable to the permutation group of Galois in his theory of
polynomial equations ( http://en.wikipedia.org/wiki/Galois_theory ).
Just as it is impossible to predict the 3-D folds of a protein based on its amino
acid sequence, so it is suggested in Row 1b in Table 6.6 that it would be impossible
to predict the nature of the chemical reaction that is catalyzed by an enzyme based
solely on the 3-D shape (also called conformers, not to be confused with
conformons of Chap. 8 ) of the enzymes alone, because the link between protein
shape and the chemical reactions it catalyzes is not deterministic but arbitrary
within physicochemical constraints (and hence quasi-deterministic), reflecting the
uncertainty about the environmental conditions under which biological evolution
has selected the particular enzyme-catalyzed reaction.
The arbitrariness of the link between the shape of an allosteric ligand and the
enzymic reaction it regulates (Row 1c) was pointed out by J. Monod (1971) who
referred to it as “gratuity.” Similarly, it is suggested in Row 1d that the link between
the shape of a transcription factor and the nature of the structural gene whose
expression it regulates is arbitrary within physicochemical constraints (i.e., quasi-
deterministic ), presumably to maximize the efficiency of the information transfer
mediated by transcription factors (Ji 1997a).
Again in analogy to the unpredictability of the 3-D protein folds from amino acid
sequences alone, so it is thought to be impossible to predict a priori the nature of the
signal transduction pathways being activated based on the 3-D shape of intercellu-
lar messengers (Row 2) such as hormones, cytokines, and autoinducers.
Finally, Row 3 in Table 6.6 suggests that there may be no inevitable (i.e.,
deterministic) link between a genome and its phenotype, including the morphology
and physiological processes of the organism involved. For example, human anat-
omy and physiology are arbitrarily related to and hence cannot be predicted from
the human genome based on the laws of physics and chemistry alone. Again, to the
extent that the link between a genome and its phenotype is arbitrary in the above
sense, the genome has been optimized in order to transfer information from one
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