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could provide fundamental clues for a new understanding of their components and
their connections with other biological levels.
Formal analyses of basic life mechanisms are strictly related to the computational
approaches. In fact, the discrete nature of basic molecular dynamics and their com-
plexity naturally requires algorithmic formulations of phenomena. Moreover, com-
putational simulations and analyses are essential tools when they are hard or even
impossible to reproduce in laboratories. In some cases the outcomes of computa-
tional experiments can suggest biological experiments, or could evaluate, exclude,
or confirm some possibilities which are expected in a given conceptual explicative
framework.
Synthetic biology, which is often advantageously associated to the computational
approaches, is a recent perspective of biological investigation which seems to be
very promising in the near future. The first objective of this discipline is the synthe-
sis of simplified cell structures, which can be components of
minimal cells
,thatis,
living organisms, according to some minimal definition of life. In this context, the
notion of
ribocell
was elaborated [143, 152], which is constituted by a lipid vesicle
containing: i) nucleotides, ii) a ribozyme which can catalyze its own polymeriza-
tion, by means of an RNA template, and iii) another enzyme able to synthesize
the membrane lipids from some suitable precursor molecules. This cell could ex-
hibit the capacity of self reproduction, in the moment that their synthesis reactions
are synchronized in the right way with their ribozymes replication. Some computa-
tional experiments show that this possibility is coherent with the data coming from
the known mathematical models of synthesis reactions (differential models). The
membrane is essentially regulated by a mechanism which, in a simple way, can be
expressed in terms of
relative surface
.If
V
is the volume of a cell and
S
is its sur-
face, then its
relative surface
is the ratio between
S
and the surface of a sphere
having volume
V
. In fact, the sphere of radius
Φ
3
V
π
3
4
is the solid with the minimal
surface comprising the volume
V
, and the tension/stretch profile in the lipid bilayer,
originated by the membrane curvature plays a fundamental role in the mechanosen-
sitivity of the cell. When the relative surface
Φ
is equal to 1, then the cell is a perfect
sphere, while if
1, then
the membrane surface is relaxed and can be split. The tolerance for the membrane
tension can be expressed by the value
Φ
<
1 the membrane is subjected to a tension, and if
Φ
>
a crisis occurs and
the surface breaks. It depends on the kind of lipid structure. For example in oleic
acid, which is used in ribocell experiments,
ε
such that under 1
−
ε
ε
=
.
0
21. A sphere of radius
R
has the
following volume:
4
3
π
R
3
V
=
therefore:
3
V
π
3
4
R
=
