Biology Reference
In-Depth Information
the primordial soup. The bulge (i.e., frustration) is located in sequence-specific
sites and carries mechanical energy,
D
E, thus qualifying them as conformons
(Ji 2000) (Sect.
8.1
).
4. The bulge acts as a template for binding a set of monomers (i.e., nucleosides
consisting of a ribose ring covalently linked to a base [symbolized as a dot connect-
ed to a bar] and inorganic phosphate ions [symbolized as a filled circle]) (Step 6).
5. The binding of the monomers and inorganic phosphate moieties to the bulge is
postulated to trigger a conformational transition of the template causing covalent
bond formation between nucleosides and adjacent
inorganic phosphates to
produce a string of nucleotides (see Step 8).
6. During the high temperature phase, the bound RNA fragments dissociate into
monomers (see Step 10), producing unchanged B and A with a part of it
reproduced (as A
0
), which has a finite probability of being elongated further
through the repetition of the thermal cycling, eventually reproducing the original
template A completely.
Pattee (1969) pointed out a set of logical and physical constraints that must be
met by any satisfactory theory of the origin of life and biological information:
1.
The primeval ecosystem language
- The global set of geophysical and geochem-
ical constraints of the primeval earth surface that were conducive to the sponta-
neous generation of self-replicating molecular systems or molecular
switches
(defined below).
2.
Complex molecular interactions leading to a very simple result
-
Communica-
tion
among molecules obey simple rules relative to the complex mechanisms
underlying their
interactions
: Communication is in some way a simplification of
complex dynamical interactions.
3.
Switches
- Physical devices whose function it is to turn on or off some physical
or formal processes driven by energy dissipation. Networks of switches often
referred to as “sequential switching machines” or “automata,” can duplicate
many of the most complex biological processes including human thought itself.
4.
Open-ended evolvability
- Not all self-replicating systems can also evolve. In
order for self-replicating systems to evolve in an open-ended manner, special
requirements additional to those of self-replication must be satisfied.
5.
Stability
- Of the many possible self-replicating systems that could have evolved
spontaneously in the primeval ecosystem, only those with
stability
,
reliability,
and
persistence
survived.
6. The “von Neumann limit
”
- There exists a critical limit to the complexity of the
network of switches which must be exceeded in order to effectuate self-replica-
tion. Since such a limit was first recognized by von Neumann, it is here
suggested that the indicated limit be referred to as the “von Neumann limit,”
that is, the minimal level of the complexity (or organization) of the physical
systems that are needed for an open-ended evolution.
All of these requirements appear to be satisfied by the combination of the
original model of the origin of biological information proposed by Anderson
(1983, 1987) and its modified version, the Princetonator (Ji 1991, pp. 224-225),
as summarized in Table
13.1
.
