Information Technology Reference
In-Depth Information
As we already mentioned, in the next evolutive step, respiration was realized by
extending the phagocytosis in a more elaborated way. In fact, the more probable
event, allowing the passage from a
prokaryote
to an
eukaryote
cell, was the
sym-
biont
phenomenon where a cell captured an
aerobic
cell with a more efficient ATP
production system based on
Oxygen metabolism
by devolving to the slave cell its
energetic metabolism. In this case, the topological transformation of Fig. 4.5 was
very appropriate, because the captured cell needs to be also compartmentalized in a
way that its reproductive activity could be controlled by the capturing cell. For this
reason, probably, a previous compartmentalization of the replicative DNA mecha-
nisms was realized, that is, the separation between DNA replication, in the nucleus,
and metabolism in the cytoplasm.
Differentiation has its deep roots in asymmetry. Even at molecule levels asym-
metric forms naturally arise. Nucleotides are chiral objects and this is a fundamental
feature for the realization of polymers conveying information. In terms of membrane
structures, asymmetry is represented by
concentration gradients
. They arise nat-
urally by consequence of general numeric properties of reaction fluxes. This result
was pointed out in a seminal paper by Turing devoted to
morphogenesis
.How-
ever, two important factors pushing toward differentiation are the
pumps
and the
gradients
. Both are surely related to the input/output direction which drives the
mechanisms of acquisition and expulsion of molecules, and to the organization of
the internal space of cells.
When different cells are integrated in a population articulated in parts, but with a
functional identity, we have a multicellular organism. The problem of this organiza-
tion is how to reproduce this identity in a reliable and efficient manner. In abstract
terms, this means:
how to memorize the knowledge underlying the biological struc-
ture of a multicellular organism, in order to be able to replicate it?
This is, first at
all, an enormous informational problem. The solution which nature found is the dis-
covery of a sort of
supercell
. This supercell is the
ovum
. It is a supercell because in
its genetic memory there is a written record of how to reproduce the whole organism
it belongs to.
Multicellularity could not be realized without this formidable biological discov-
ery. From embryogenesis [163] we know that the construction of the organism from
ovum (here there is no commitment with the sexual or asexual reproduction) fol-
lows a progressive differentiation, and this is the basis of the so-called
evo-devo
paradigm (the developmental itinerary resembles the evolutive one); therefore the
ovum logic is strongly related to the differentiation logic and is the same kind of
phenomenon underlying
stem cells
,
totipotent
, and cellular type reversibility and
irreversibility, all concepts which are crucial in the new perspectives of many thera-
peutic approaches. The human body has around 250 main cellular types. They have
the same genome, but only a part of it is active in each type. This is a great redun-
dancy from the point of view of any system designer. But the motivation of this lack
of economy depends on the evolutive logic of the differentiation process.
The
reusing of acquired competencies
principle, which we already noticed, is
a general device driving the evolutive steps of life. However, another principle is
more specifically involved in the differentiation and organization steps along the
