Editorial board editor-in-chief

Keybords:
Life, Protein aggregation, Eryptosis, Erythrocyte
In search of a deinition of life
Our understanding of nature and its mechanisms improves gradu-
ally with increasing knowledge of biology. However, the concept 
of life as a phenomenon remains ambiguous [1]. It is apparently 
obvious but still elusive. It is expected that progress in the knowl
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edge of the molecular mechanisms will provide further insights 
into the issue. Some scientists compare the dificulties relating 
to the deinition of life to those encountered while describing 
the properties of water or ire until focusing interpretation on the 
molecular structure [2]. Because of problems in deinition life is 
usually described as a set of signs listed from the viewpoint of 
metabolism, biochemistry, genetics and thermodynamics. How
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ever, this descriptive classiication does not explain the complexity 
of life as a process. When using this deinition some evidently 
inanimate objects are sometimes classiied as living organisms 
and vice versa. Newer deinitions combine the concept of life 
with the genetics. Living things are systems that are capable 
of self-reproduction, mutation and natural selection [3]. Life is 
also a self-sustained chemical system capable of undergoing 
Darwinian evolution [4].
Self-organized and self-sustaining biological systems are 
classiied as living organisms. This deinition is too general and 
does not delimit precisely the boundaries of life. There is still 
controversy regarding criteria for classifying biological forms, 
especially subcellular, as living things. This concerns for instance 
viruses. In contrast to bacteria, viruses do not have independent 
metabolism and despite their biological origin they usually are 

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System biolog
y
24
The criteria of life and aging from a molecular viewpoint…
not regarded as living organisms. There are also cybernetic and 
thermodynamic approaches to describe living things [5].
In thermodynamics, systems in which some processes occur 
are divided into open and closed systems. Reversible processes 
occurring in closed systems, not linked with the surroundings, 
tend to reach an equilibrium, which occurs when the reactions 
in both directions are taking place at the same velocity. This 
moment is regarded as the end of the reaction. In the cell this 
state is attained upon its death. However, life is sustained only 
by processes that occur spontaneously as a result of maintaining 
non-equilibrium states. These are states, in which the process is 
still organized and occurs spontaneously (Fig. 1).
Fig. 1.
Reaction kinetics in the model system with
non-equilibrium and dynamic equilibrium states indicated
by arrows
Maintaining non-equilibrium states is possible only with per-
manent exchange of the reaction components with the surround-
ings, that is, in open systems where inlow and outlow of the 
components maintain the reaction. However, the attainment of the 
speciic, stable level of process-related activity in such systems 
requires regulation. Only negative feedback auto-regulation may 
assure stability in the situation where inlow and outlow of the 
reaction components is dependent on the surroundings, that is, it 
is prone to oscillation. The omnipresent automaticity in complex 
biological processes stigmatizes the cells and the organisms and 
is interpreted as the characteristics of life.