deviations testify to the viewpoint that it has evolved from a simpler form
(when it has been encoding a smaller number of amino acids) to a more
complex one imposed by the evolution of living systems.
Based on the assumption for a smaller number of amino acids needed
for the ancient proteins and the one of the possibility for protein synthesis
without the participation of nucleic acids O. Ivanov (1989 b) has grounded
the idea expressed later also by other authors (Juckes, Osawa, 1990)
about the existence of a more ancient, simpler genetic code corresponding
to a smaller number of amino acids (the two first bases of the codon are
valid). Davydov (1989) has launched the idea for the existence of a reverse
genetic code i.e. a dependency between the structural and chemical
properties of the amino acids and the corresponding codons.
The publication of Kolyassnikov (1993), in which on the grounds of his
tetrameric model of water has suggested the hypothesis that water has
served as matrix for the polymerization of amino acids and nucleic acids,
has arisen a great deal of discussion. This idea of his is very attractive but it
needs serious proofs.
The exceptions pointed out give grounds for the conclusion that the
genetic code is not universal and has undergone an evolution from a simpler
to a more complex mechanism. The accumulation of more data and facts in
that respect would help to make clear the third “white spot” in biology.
Metabolism
The term metabolism (Greek: metabolé — change) denotes the exchange
of substances in living systems. This problem will be treated with the
intention of giving its development in retrospect and by no means
attempting to fully cover it, so as to mark the evolutionary path from the
cells since their emergence, trace their further development and their
incorporation into the more complex multicellular organisms.
In order to throw light on the issue a short review of the well-known facts
is needed. All cells are divided basically into two groups: autotrophic cells,
which can synthesize the organic compounds necessary for their functions
from inorganic substances and water using CO₂ from the atmosphere, and
heterotrophic ones, which are in no capacity to assimilate CO₂ and satisfy
their needs with organic products synthesized by other organisms.
Depending on the source of energy they are phototrophic — such using
solar light and chemotrophic — which use the energy derived from redox
processes. Besides, the cells are also divided into anaerobic, in which
metabolic processes take place in the absence of oxygen and aerobic, in
which they are accomplished with the participation of oxygen. Some of them
are obligatory anaerobes and respectively aerobes while others are
facultative ones, since they can exist both in absence and in presence of
oxygen. Metabolic adaptability is observed even in higher plants where the
cells containing chlorophyll are autotrophic and the ones of the roots show a