Biology Reference
In-Depth Information
Fig. 11.11 A comparison between the architecture of the computer and the living cell (Reproduced
from Wang and Gribskov 2005).
CPU
central processing unit,
I/O
input/output device
is stable even when the computer is turned off. This is reminiscent of the metabolic
difference between RNA and DNA in cell biology; the former levels are changing
with cell functions, disappearing when the free energy sources are turned off
(Garcia-Martinez et al. 2004; Ji et al. 2009a), while the latter is relatively stable
in cells, maintaining its sequence information even when cells are deprived of free
energy. The dynamic nature of RNA levels in cells is the consequence of the fact
that RNA is both produced via the transcription process and degraded via the
transcript degradation process simultaneously and with comparable kinetic
computer and the cell is that, just as the CPU of the computer cannot utilize the
information stored in the secondary memory without first converting it to
the primary one, the cell cannot utilize the genetic information encoded in DNA
without first converting it to RNA and then to proteins, since the utilization of DNA
information requires
free energy dissipation
which in turn requires proteins acting
as catalysts for free-energy supplying chemical reactions (Fig.
11.12
).
Another way to describe the fundamental difference between DNA and RNA is
in terms of the concepts of
equilibrium
and
dissipative
structures (Babloyantz 1986;
Kondepudi and Prigogine 1998; Prigogine 1977, 1980; Kondepudi 2008). DNA is
an equilibrium structure and RNA levels are dissipative structures, for the obvious
reason that the former remains and the latter disappears when free energy input into
the cell is blocked as mentioned above (Sect.
3.1
). The concentration of DNA in
cells remain more or less constant except during the S phase in the cell cycle,
