Biology Reference
In-Depth Information
from physical chemistry and then not only in terms of their precise meaning, but
perhaps also in terms of their structure. Perhaps such biological theories will be
less general, more condition dependent, and much more complex. This remains
to be seen. Automated hypothesis generation from experimental data may show
new ways in this respect (King et al., 2004).
3.4. Systems biology
Our contention that the molecular biology of living systems is neither physics
nor biology, but rather a science in its own right, suggests that it is entitled to
a name. Such names already exist, i.e. systems biology and integrative biology.
We shall here use the former. We propose that systems biology attempts to
establish principles of operation of biological systems such as the living cell.
It should thereby find its own concepts rather than reduce them to physical
chemistry. It should strive to be quantitative enough to be able to understand the
emergence of functional properties from nonlinear interactions between com-
ponents of biological systems. It should also appreciate that such interactions
depend on the precise state that the biological system is in. This has the con-
sequence that laws should address specific conditions rather than be completely
general. For instance a law could be that the glycolytic pathway can engage
in oscillations provided that the elasticities of the following stated reactions
fall within the following range . The law should not be of the generality
of physics i.e., that the glycolytic pathway might engage in oscillations under
any, unspecified conditions. Systems biology should synthesize the following
features
(1) Information on expression levels is contained in the DNA and is expressed
through mRNA into proteins which then catalyse reactions.
(2) The expression levels are not simply determined by transcription activities
of the DNA in a dictatorially hierarchical fashion, but controlled by a
combination of extracellular signals and intracellular concentrations.
(3) The concentrations of intracellular substances are determined by all the
intracellular processes and extracellular signals together.
(4) The intracellular processes are determined by the expression levels of
the enzymes, by the kinetic parameters of those enzymes, as well as by
extracellular signals and intracellular concentrations.
(5) Much of biological regulation is one of circular or spiraling causality
(Rosen, 1991; Westerhoff & Hofmeyr, 2005), i.e. a concentration of a
substance may co-determine the concentration of another substance at later
times and be co-determined by the concentration of that other substance at
earlier times.
