Information Technology Reference
In-Depth Information
In the middle of the 19th century, the discovery of DNA structure [63], and its
informational and digital nature, introduced a new level in the analysis of life phe-
nomena [1]. From this perspective, discrete information becomes the basis of crucial
molecular processes inside the cell, and it follows that their logics can be completely
understood if their symbolic role is recognized. In fact, DNA molecules represent
symbols, and the discrete nature of these molecules implies the digital nature of pro-
cesses involving them. Biochemistry provides nanotechnological support to sym-
bolic elaborations, which follow principles analogous to those of formal systems
investigated in formal language theory or mathematical logic.
1.1.1
Molecules and Protocells
According to some cosmological evaluations, at very beginning, about 10
10
years
ago, and in a time interval between around 10
−
44
and 10
−
35
seconds, at a tempera-
ture near 10
28
Celsius degrees, matter appeared as subatomic particles. After a very
short fraction of one second, they aggregated into the simplest atoms, from Hydro-
gen to Helium, Lithium, Beryllium, Boron, Carbon, Nitrogen, Oxygen, Fluorine,
and Neon (the list is only an exemplification reporting the first period of Mendeleev's
table) [3]. Then, the simplest organic molecules of hydrocarbons (carbon aggregated
with hydrogens) appeared. In fact, the carbon atom has a structure which implies an
enormous combinatorial power of aggregations (we do not enter into more details,
but this aspect is related to its specific “tetravalent” nature). From hydrocarbons the
organic molecular evolution starts, which is the basis for the emergence of life.
The more complex organic molecules are constituted by carbon, hydrogen, oxy-
gen, nitrogen, and other crucial atoms (for example, phosphorus, sulfur, iron, cal-
cium, potassium, sodium, chlorine). They are capable of providing a very rich
catalog of chemical aggregations (hydrocarbons, alcohols, ethers, esters, amides,
amines, fatty acids, and other organic groups) [4].
The prebiotic molecular evolution is the process at the end of which, from these
basic organic molecules, more complex molecules emerged, which provided the
basic pieces for the chemical realization of
polymers
and
membranes
[10, 6, 199].
Protocells are biomolecular aggregations which:
i)
separate an inner region from the external environment, by means of mem-
branes,
ii)
select within this internal region some kinds of molecules,
iii)
concen-
trate the molecules which are inside, for a better chemical interaction,
iv)
protect
the internal space from external disturbances to the internal activity, and v) take
matter from outside and expel matter outside for feeding the internal processes and
eliminating matter which degrades or is dangerous to the internal activity.
These five points, referring to the compartmentalization of molecules, are real-
ized by membranes. However, point ii) is not enough for an efficient realization of
chemical transformation. In fact, vicinity in space is important, but some agents are
necessary which recognize reactants and speed up their reactions, that is, which play
aroleof
catalysts
. This role can be played by complex molecules, able to discrimi-
nate forms. Linear polymers provide a solution to this complex task. By using some
