The Minimal Cell: A Problem of Evolution 1/2

Human genomics pioneer Craig Venter has revived his
project of artificially constructing a bacterium. Venter's
company Synthetic Genomics will take the bacterium with
the simplest known genome, Mycoplasma genitalium, a
parasite that lives in the human urogenital tract, and remove
each of its 517 genes one-by-one until the minimum gene
set is reached for the organism to survive in a controlled
environment.

Earlier theoretical studies by Mushegian and Koonin
predicted that the minimum bacterial genome would be 256
genes. Gene knockout experiments on M. genitalium by
Venter's The Institute for Genomic Research found
that the minimum genome for a bacterium was 265 to 350
genes.

However, the Mycoplasmas are parasites and cannot live
outside their host or the laboratory, lacking the genes to
synthesise all their metabolic requirements.¹ Indeed, of all
bacterial genomes sequenced to date those that fall below
1,500 gene products (proteins and RNAs) belong to
parasites. Free-living organisms (those capable of
permanent independent existence) seem to require a
minimum of between 1,500 and 1,900 gene products.²

A gene is made of nucleic acids (DNA or RNA), and as Michael
Behe explains, "Imagining a realistic scenario whereby natural
processes may have made proteins on a prebiotic earth-
although extremely difficult-is a walk in the park compared to
imagining the formation of nucleic acids such as RNA. The
big problem is that each nucleotide `building block' is itself
built up from several components, and the processes that
form the components are chemically incompatible."³ Atheist
origin of life theorist Robert Shapiro regards the chance origin
of a ribozyme (a self-replicating strand of RNA) to be equivalent
to the idea that a golf ball could play its own way around a
difficult golf course, at well-under par, without the golfer!⁴

Another atheist origin of life researcher, Cairns-Smith, based
on the 14 steps, each comprising an average of 10 sub-steps,
that a chemist would take to synthesise a nucleotide, estimates
that the probability of the spontaneous generation of even
one nucleotide to be of the order of 10^-109, which is 1 chance
in 1 followed by 109 zeros!⁵ By comparison the number of
elementary particles in the universe are estimated to be 10⁸⁰.

Yet M. genitalium has 580,070 nucleotide base pairs with
each gene being an average of 1,040 base pairs.⁵ Even
assuming the lower minimum of 256 genes necessary for life,
and an average of 1,000 base pairs per gene, that is a
requirement that no less than 256,000 nucleotide base pairs
would have to spontaneously self-assemble.

But as we shall see in part 2/2, that is just the start of
evolution's problem with the minimal cell!


References
1. Morowitz H.J., "Beginnings of Cellular Life: Metabolism
Recapitulates Biogenesis," Yale University Press: New Haven
CT, 1992, p.67.
2. Rana, F.R. & Ross H.N., "Origins of Life: Biblical and
Evolutionary Models Face Off," Navpress: Colorado Springs CO,
2004 pp.162-163.
3. Behe, M.J., "Darwin's Black Box: The Biochemical
Challenge to Evolution," Free Press: New York NY, p.171.
4. Shapiro R., "Planetary Dreams: The Quest to Discover
Life beyond Earth," John Wiley & Sons: New York NY, 1999,
p.104.
5. Cairns-Smith A.G., "Seven Clues to the Origin of Life: A
Scientific Detective Story," [1985], Cambridge University
Press: Cambridge UK, 1993, reprint, pp.46-47.
6. Fraser, C.M., t al., "The minimal gene complement
of Mycoplasma genitalium," Science, Vol. 270, October 20,
1995, pp.397-403.


Stephen E. Jones
"Problems of Evolution"