Biology Reference
In-Depth Information
If the molecules did not follow the unequivocal rules of associa-
tion, this problem would be even greater in the case of more com-
plex cell structures involving a much larger number of molecules.
The possibilities for combination would then be enormous and the
probability of forming a functional structure from among all those
which are possible would be very slight. Ontogenesis would no longer
be a deterministic but a probabilistic mechanism, which would obvi-
ously be contrary to genetic determinism.
The idea of stereospecificity therefore involves the unequivocal
character of molecular interactions. To form a complex structure,
biological molecules have to fit together excluding chance, like the
pieces of a puzzle. At this price, we can understand the mechanism
of genetic determinism. An organism is constructed gradually from
the stereospecific order of the molecules per organisation level,
depending on a series of causal determinations running from the
genome to the phenotype: 1) the proteins are synthesised from the
genes; 2) the proteins assemble stereospecifically to form cellular
organelles and cells; 3) due to the exchange of specific signals car-
ried by the proteins, the cells recognise each other and form tissues
and organs; 4) the process ends with the organism which was coded
in the genome being produced (see Fig. 11; CN pp. 93-94). Each of
these levels, called an 'integron' by François Jacob, is produced by
the integration of specific interactions of the lower level (Jacob,
1970). Owing to the 'central dogma of molecular biology', the
process occurs only in one direction, always from the genotype to
the phenotype. It is the genome therefore, that, according to this
consensus vision established in the 1960s, holds the power of organ-
isation. The genome is the cause of the phenotype in the strongest
sense of the term, carrying the coded representation of the organ-
ism, and determines the mechanisms of cell morphogenesis.
This theory helps in understanding the reasoning behind molec-
ular biology research efforts, which consist of systematically isolat-
ing genes and proteins and subsequently, sequencing the human
genome. Indeed, if all biological phenomena were supported by stereo-
specific interactions, it should be possible to characterise a protein
