life processes (see the last paragraph of Section 2. 6). That is probably
why the number of enzymes is incredibly great, so that they can carry
out their numerous and various functions.
This assumption raises the question whether a bacterial cell (e.g. E.
coli), if it is to perform exactly the scheme prescribed to it by man for the
protein synthesis, would be able under optimum conditions to complete
its development cycle and divide for 20 or 30 min which is in fact easily
accomplished. The doubts in this respect are huge. That is why the
opinion expressed by Alberts et al. (1986) is considered true and is
gladly shared: “…Molecular processes underlying protein synthesis are
exceptionally complicated and their study has only been accumulation of
facts for the time being, without encompassed in a comprehensive
theory. The discovery of the mechanisms involved in protein synthesis
could throw some light as well on those early events related to the origin
of life itself”. Besides, the authors accepted that from a chemical point of
view proteins are “the most complex of all molecules known”.
The problem of protein self-replication without the participation of
DNA remains unsolved. This is a heresy since it contradicts the Central
dogma in molecular biology, accepting only DNA as the unique molecule
endowed with such a capacity. A great interest is provoked by the data
of Lee et al. (1996) on the existence of self-replicating peptide. In the
literature there are also other studies in that trend. If it is confirmed more
convincingly, it will be important for the throwing light on protein
synthesis especially in the early stages of the evolution of living matter
and cell structures.
Nucleic Acids
As a result of the prolonged studies on nuclein two types of nucleic acids
were discovered — deoxyribonucleic acid (DNA) and ribonucleic acid
(RNA). They proved to be long polynucleotide chains of great biological
importance. They are built from four bases each, which in combination
with one of the pentose sugars and phosphate residues form the
corresponding nucleotides (Fig. 2–37). The differences between them are
expressed in the following: DNA contains deoxyribose while RNA
contains ribose; thymine in DNA is replaced by uracil in RNA. The binding
of the nucleotides leads to the formation of long polynucleotide chains of
DNA and RNA (Fig. 2–38).
The biological role of DNA was made clear after the discovery of its
spatial structure. The history of this great discovery is very thrillingly
described in J. Watson’s book “The Double Helix” (1968, 1975).