Information Technology Reference
In-Depth Information
than one pathway are the main mechanisms of metabolic flexibility conferring
robustness to a biological system.
The essential character of a given mutation as provided by network
topological invariants, although derived from laboratory experiments and not in
the natural environment where the competitive pressure is active, opens the
possibility to consider the metabolic network wiring structure as a biological
entity that, even if immaterial, deeply influences the behavior of the organism.
This considerations are reinforced by the possibility to derive phylogenetic
trees by the comparison of metabolic network wiring patterns of different
organisms so demonstrating that metabolic network topology is influenced by
evolution process. In other words, metabolic network wiring is a phenotype as a
whole, sensing the adaptive history of the organism.
8.2.2.
Evolution of network topologies
In the process of adaptation of an organism to its particular environment, during
evolution, what is actively exposed to selective forces is the so called
'phenotype' i.e. the entire set of behavioural, physiological, structural,
biochemical features of the organism.
On the contrary the 'genotype' is considered as the hereditary information
being transmitted thru different generations. If, and only if, a given phenotypical
feature offering a specific advantage is determined by a genotypic change, it will
be passed across generations and an evolutive step will be achieved.
The somewhat revolutionary acquisitions that followed the completion of the
so called genome project abruptly changed our notion of what a 'genotype' is in
phenotypic terms. Until twenty years ago everyone could answer 'genotype is the
DNA sequence of a given organism'. As for now, the discovery of RNA editing,
epigenetic heredity in terms of DNA methylation patterns, post translational
modifications and so forth do not allow us to give a satisfactory answer to the
question.
Notwithstanding that, we can safely assign, to different biological entities
their relative distance from the 'pure phenotypic' (from Greek 'what appears,
what is observable') or 'pure genotypic' (from Greek 'what generates', 'what
produces') poles. Thus metabolic network wiring is a classical phenotype, given
this wiring is the image in light of the repertoire of chemical reactions that are
specifically catalysed in a cell producing its chemical make-up with wich the cell
responds to environmental stimuli.
On the contrary, the aminoacid sequence of a specific enzyme of this
network, even being - strictly speaking - a phenotype (depending on the
