Researchers today are actively
seeking and finding new ribozymes. Many are artificially engineered and others arise from
random sequences. Many of these researchers believe that in time they will find a self
replicating RNA molecule. Others like Joyce and Orgel who are at the forefront of the
research disagree.
In chapter 7, several techniques used by life to circumvent the second law of
thermodynamics were discussed. Unless a self replicating RNA molecule has the capability
to implement some of these same techniques, its existence can be ruled out on purely
theoretical grounds.
Based on fundamental laws of physics, science can state with certainty that
if a self replicating RNA molecule is found, the molecule will only be able to replicate
in a test tube. It will require a continuous supply of activated nucleotides to drive its
replication. While this might work in the test tube, it will certainly not work in the
primordial soup. Activated nucleotides in the soup will not last for more than a few days.
Given that their decay will dominate any conceivable path for prebiotic synthesis, the
soup will only contain at most a very dilute supply of activated
nucleotides. Given the difficulty associated with the prebiotic synthesis of
ribose, adenine, and cytosine, the concentration of these critical molecules in the soup
will also be extremely low. This means that the first successful self replicating RNA
molecule must be able to direct the synthesis of adenine, cytosine, ribose, uracil and
guanine. If it cannot do this, it will not be able to replicate in the soup. Furthermore,
it must be able to activate all of the nucleotides. So this special RNA molecule must know
how to tap a plentiful energy source and use it to drive many different chemical
reactions. If it cannot perform all of these functions, then it is a perpetual motion
machine, and its very existence is limited to biology textbooks.
Figure 10.2: A Self Replicating RNA Molecule
In figure 10.2, the RNA molecule can exist in two states, folded and
unfolded. When folded, it catalyzed RNA replication, and the formation of adenine, ribose,
cytosine, uracil, and guanine. It also must create activated nucleotides (not shown). When
unfolded, it serves as a template for replication. The folded version must also know how
to replicate the unfolded version.
This particular ribozyme taps into sunlight as an energy source using a
primitive form of photosynthesis. Other self replicating RNA molecules could potentially
oxidize a chemical like methane, hydrogen, or sulfur to generate the required energy.
Figure 10.2 is what is required of a “living molecule.” Anything
less is not alive. This figure was construted with due consideration to the second law.
Any RNA molecule that does not possess all of the capabilities shown in figure 10.2 is a
perpetual motion machine. It may replicate in the lab as long as it is supplied with
activated nucleotides, but it will not replicate in the soup. Thus, it only exists in
textbooks, and there is no need to wait to see if researchers can locate it.
Inventors have been trying to invent perpetual motion machines for at least
2000 years. They have all failed. Nevertheless, many have been issued patents by various
governments throughout the world. Two examples of perpetual motion are shown in figure
10.3. Both examples are equally absurd. While many scientists apparently only recognize
the absurdity of the first picture, nature can recognize both, and it does not allow
either to exist.
Figure 10.3: Perpetual Motion Machines
The first picture in figure 10.3 is a clear violation of energy
conservation. It does not work because the force that the magnet exerts on the car is
exactly cancelled by the force that the car exerts on the magnet. The magnet does not
cause the car to move. The second violation is more subtle only because it violates a
different law of nature. When a self replicating molecule replicates, the replication
decreases the entropy of the universe. The second law is violated. To get around this
problem, any real self replicator must know how and be able to couple its replication to a
plentiful energy source. If it is unable to do this, then it is a special type of
perpetual motion machine, and it only exists on paper and in the imagination of
researchers.
This observation is perhaps one of the strongest line of evidence that supports
intelligent design. The requirement of knowing how to couple an energy source to do work
is found in all living things. The second law explains why it is necessary. Self
replicating systems also need to do this, and this requirement prevents them from being
simple. Science just does not have a good explanation for the origin of life.
References:
1) Lee, Granja, Martinez, Severin, Ghadiri, “A Self Replicating Peptide,”
Letters to Nature, 382:525-528, 1996.
2) Joyce, Visser, Boeckel, Boom, Orgel, Westrenen, “Chiral Selection in Poly (C)
Directed Synthesis of Oligo (G),” Letters to Nature, 310: 602-604, 1984.
3) Joyce and Orgel, The RNA World, Gesteland, Cech, Atkins, Cold Spring Harbor,
“Origin of the RNA World,” 1999.
4) Bartel, The RNA World, Gesteland, Cech, Atkins, Cold Spring Harbor, “Recreating an
RNA Replicase,” 1999.
5) Ekland, Szostak, Bartel, “Structurally Complex and Highly Active RNA Ligase
Derived from Random RNA Sequences, ” Science, 1995.
6) Bartel and Szostak, “Isolation of New Ribozymes from a Large Pool of Random
Sequences,” Science, 261:1411-1418, 1993.
7) Thaxton, Bradley, Olsen, The Mystery of Life’s Origin: Reassessing Current
Theories, Philosophical Libraries, 1984.
8) Orgel, Self-organizing Biochemical Cycles, Salk Institute of Biological Studies,
99:12503-12507, 2000.
9) Green, Szostak, “Selection of Ribozyme that Functions as a Superior Template in
Self Copying Reaction,” Science, 258:1910-1915, 1992.
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