Life Strategies - Infobiotics: Information in Biotic Systems - page 170

facts shows in a more evident way the logical nature of the enzymatic paradox and
of its solution:

1. Fact 1. Every biochemical reaction needs an enzyme catalyzing it.
2. Fact 2. Every enzyme is either internally produced by the cell, or introduced
into the cell from the outside.
3. Fact 3. The introduction of an enzyme in the cell has to be selective (not any
enzyme floating in the external environment can be internally introduced).
4. Fact 4. A selective introduction of an enzyme in the cell needs a specific
molecule which needs a specific enzyme producing it.
5. Fact 5. The previous facts imply either a regressio ad infinitum , or a contradic-
tion in both cases of internal production or external introduction of enzymes.
6. Fact 6. A different kind of external introduction can avoid the consequences
of the previous facts: an introduction of special molecules in the cell from the
mother cell. They are I-molecules which are not enzymes, but provide the nec-
essary information for internally producing the enzymes of a cell.
7. Fact 7. I-molecules need to be replicated in the cell by enzymes already present
inside it, otherwise the passage from the mother to the daughter cell should
imply the death of the mother cell.
8. Fact 8. According to the previous fact, life is based on heredity and I-molecules
are the molecular basis of this mechanism.
9. Fact 9. A more reliable and efficient mechanism for molecular heredity is
reached by a unique I-molecule collecting all the information for the synthe-
sis of enzymes.
10. Fact 10. The solution of the enzymatic paradox, outlined by the previous facts,
is based on reproduction and on heredity. In reproduction, the replication of
molecules is realized in the context of metabolism and vice versa metabolism
is realized by means of mechanisms of molecule replication.

4.1.1 Genes and Proteins

So far we have concentrated on enzymes. They provide the basic metabolic activ-
ity of cells, but bio-molecules performing the basic functions of cells constitute the
larger class of proteins . In fact reactions need to be catalyzed, but also regulated.
Moreover, bio-molecules for recognizing, transporting molecules, and for perform-
ing signals and movements are also essential in a cell as well as bio-molecules for
assembling specific structural components (gates, tunnels, reticula, bases, histones,
cilia, and so on). Table 4.1 summarizes the basic functions of proteins.
Amino acids are the monomers of polypeptide sequences. They are encoded by
triples of RNA nucleotides. However, this encoding is partial and redundant. This
means that some of all possible triples over the alphabets

, which do not
encode amino acids, as is the case of triples UAA , UAG , UGA are not encoding, while
many triples may denote the same amino acid. Table 4.2 gives this correspondence,
called genetic code , where a letter of the English alphabet is associated to any amino
acid, and sets of codons encoding the same amino acid are synthetically denoted by

{ A , U , C , G }