Biology Reference
In-Depth Information
scopic level. For example, the binding of a ligand to a cell surface receptor can
influence what happens in the center of the nucleus 5-10
m
m away, suggesting that
correlation lengths
in cells at critical points can be 5-10
m
m, which is much longer
than the persistence length (i.e., the length over which mechanical forces can be
transmitted owing to stiffness) of biopolymers, typically less than 0.1
m
m (Bednar
et al. 1995). The Bhopalator model of the cell suggests that there are three possible
mechanisms for effectuating the micro-meso correlations or couplings:
1. Mechanical mechanisms mediated by the cytoskeleton as has long been
advocated by Ingber and his group (1998)
2. Chemical mechanisms mediated by diffusible molecules and ions as are well
established in signal transduction pathways (Kyriakis and Avruch 2001) and the
actions of transcription factors and
3. Electromagnetic field mechanisms as evident in various membrane potential-
dependent processes such as voltage-gated ion-channel openings and closings
Unlike in condensed matter physics where long-range correlations (e.g., snow
crystal formation [Libbrecht 2008]) are driven solely by the free energy of
interactions among molecular components, the long-range correlations seen in cells
are driven by both
free energy
and
genetic information
, because both of these factors
are essential in the operation of enzymes as catalysts (see information-energy com-
plementarity in Ji (2002b, 2004a, b)). Thus, it may be concluded that the role of
enzymes are what distinguishes biotic and abiotic critical phenomena exhibited, for
example, by living cells.
2.5 The Theory of Finite Classes
Bohr thought that biologists should accept the
functions of living systems
as given,
just as physicists accept
quantum of action
as an irreducible unit of physical reality
at the microscopic level. This is the essence of the
holism
in biology that Bohr
suggested seven decades ago. This seminal idea was further developed and
elaborated on by W. Elsasser from the 1960s through the 1990s, laying the logical
foundation for Bohr's intuitive grasp of the essence of the phenomenon of life.
Hence, we may well consider Bohr and Elsasser as the originators of
holistic
or
systems biology
that has been gaining momentum in recent years (Hartwell et al.
1999; Bechtel 2010).
Elsasser dedicated the last three decades of his life to the theoretical research
aimed at defining the basic difference between physics and biology. He maintains
that the class of the objects studied in physics is
homogeneous
in kind and
infinite
in
size (in the order of Avogadro's number, ~10
23
), whereas the class of objects
studied in biology is
heterogeneous
in kind (the number of different kinds in this
case being in the order of 10
10^9
, the number of all possible strings that can be
constructed out of the different kinds of deoxyribonucleotides, one billion units
