Multicellular Systems - Molecular Theory of the Living Cell - page 515

Table 15.1 The roles of DNA, RNA, and proteins in Drosophila embryogenesis
DNA RNA Protein

1. Average size
(arbitrary unit)

3 2 1

2. Diffusibility
(arbitrary unit)

1 2 3

3. Effective range
of action

(a) Nucleus (a) Nucleus (a) Nucleus

(b) Cytoplasm (b) Cytoplasm

(c) Extracellular space

4. Catalytic
activity

No Almost none Yes

5. Function Secondary

memory
(Sect. 11.2.6 )

Primary memory
(Sect. 11.2.6 )

Soft transistor
(Sect . 5.1.1 )

Optimal form for
information
reproduction

Optimal for
information
retrieval

Optimal form for energy
transduction a

Molecular computing
Cell language
(Table 6.3 )
a From chemical to mechanical forms, i.e., conformons (Chap. 8 )

to meet its needs by balancing the rates of production (V P ) and the rates of
degradation (V D ) of RNA (see Steps 1 and 2 in Fig. 15.2 ). Depending on the
needs of the cell, the concentrations of intracellular levels of specific RNA
molecules are actively maintained at one of the following three dynamic states:
1. Dynamic steady states (when V P ¼ V D ),
2. Ascending states (when V P > V D ), and

3. Descending states (when V P < V D ).

Recent evidence indicates that V P and V D are space- and time-dependent, often
regulated by microRNAs (Makeyev and Maniatis 2008), thereby qualifying space-
and time-dependent RNA levels as members of dissipative structures and, more
specifically, members of IDSs or r-dissipatons (see Sect. 3.1.2 ).
The Triadic Control Principle (or Hypothesis) depicted in Fig. 15.2 is so called
because of the existence of two opposing processes, 1 and 2, under the control of a
third process, 3. The source of the control signals, or the agent of the cell control, is
postulated to be the cell itself which is in constant communication with its
neighbors and environment (by exchanging information carried by diffusible
molecules or through local electric fields) and perform molecular computation
under the guidance of DNA programs (sheet music). This postulate is consistent
with or equivalent to the postulate that the cell is the smallest DNA-based molecular
computer or the Computon (see Row 9 and Footnote 7 in Table 6.3 ) (Ji 1999a). The
modifier, “triadic”, also implies (1) that there are three, and only three, classes of
the processes underlying cell functions, namely, production, degradation , and