Biology Reference
In-Depth Information
but include dynamic, multisubunit complexes (e.g., hyperstructures of Norris et al.
(1999, 2007a, b)) that are formed transiently to carry out needed metabolic functions
and disassemble when their work is done. In analogy to the concept of
activity
coefficients
in physical chemistry (Moore 1963, pp. 192-195; Wall 1958, pp.
341-344; Kondepudi and Prigogine 1998, pp. 199-203), we may define what may
be called “
bioactivity coefficient
,”
b
, as follows:
b
i
¼
C
a
;
i
=ð
C
a
;
i
þ
C
i
;
i
Þ¼
C
a
;
i
=
C
t
;
i
(3.6)
where
b
i
is the
bioactivity coefficient
of the ith component of the cell, C
a,i
is the
concentration (i.e., the number of molecules in the cell) of the
active form
of the ith
component, C
i,i
is the concentration of the ith component in its
inactive form
, and
C
t,i
is the total concentration of the ith component. Therefore, the
active
or
effective
concentration
of the ith cell component is given by
C
a
;
i
¼ b
i
C
t
;
i
(3.7)
The mechanisms by which a component of the cell is activated or inactivated
include (1) covalent mechanisms (e.g., post-replicational and post-translational
modifications such as phosphorylation, methylation, acetylation, formylation, pro-
tonation, reduction, oxidation, etc.), and (2) noncovalent mechanisms (e.g., confor-
mation changes of biopolymers and their higher-order structures induced by pH,
ionic strength, mechanical stresses, local electric field, and ligand binding).
The bioactivity coefficient as defined in Eq.
3.7
is synonymous with the “frac-
tional activity of biomolecules,” namely, the fraction of the total number of the ith
biomolecule that is activated or active at any given time
t
at a given microenviron-
ment located at coordinates
x, y,
and
z
. In other words,
b
i
in Eq.
3.7
is not a constant,
as activity coefficients are in chemistry, but a function of space and time, leading to
the following expression:
1
>b
i
ð
x
;
y
;
z
;
t
Þ
0
(3.8)
Inequality
3.8
states that the activity of the ith biomolecule inside the cell is
dependent not only on the intrinsic physicochemical properties of the molecule
itself but also on its microenvironment and time. We may refer to this statement as
the Principle of the Space-Time Dependent Bioactivity Coefficient (PSTDBC).
PSTDBC is consistent with the “metabolic field theory of cell metabolism,” also
known as “cytosociology,” formulated by Welch and his colleagues (Welch and
Keleti 1981; Welch and Smith 1990; Smith and Welch 1991). It is very likely that
PSTDBC has provided important additional degrees of freedom for the living cell to
complexify its internal states, thereby enhancing its survivability in the increasingly
complexifying environment of the biosphere over the evolutionary time scale
