There is much more than what meets the eye in the recent experiment 1 of Craig Venter’s group. For example it clearly demonstrates the primacy of genomic processes over cell processes in the case of the synthetic genome and there is no reason why it will be different if the genome is natural.
Transplantation of the synthetic genome of Mycoplasma mycoides into Mycoplasma capricolum replacing the genome of Mycoplasma capricolum resulted into the creation of new Mycoplasma mycoides cells that are controlled only by the synthetic chromosome.
Under the conditions of Venter’s experiment the genome of M. mycoides acted as a system that is not influenced by its surrounding environment [the cell environment of M. capricolum] but dismantled the surrounding environment to build and control its own surrounding environment [the cell environment of M. mycoides] as per its genetic programs.
In a way the synthetic genome of Mycoplasma mycoides acted as a self controlled machine that built its own cell structure in operation. This indeed reminds us of the intricate machine of George Wald 2 which is now synthesized by the Venter’s group.
During eighties scientists held the view 3, “The molecules in cells are guided by the same basic laws of chemistry and physics that apply through out the universe…… The mystery lies rather in the programmed coordination of the myriad of chemical reactions necessary for the metabolic activities of the cells”. Venter’s experiment shows that bio chemical reactions within the cell are controlled by the genome [amount of DNA 3 required to specify the organism] and controlled execution of genetic programmes is the intrinsic property of the genome for the central dogma of Crick precludes the other way. Thus it is the genetic programmes and the ability of genome to execute those programmes that are responsible for the programmed coordination of bio chemical reactions within a cell.
A machine in controlled operation is about maintaining an unstable state. We see this in the cases of higher organism in terms of maintaining higher percent of thermodynamically less stable Adenine-Thymine nucleotide pairs than Guanine-Cytosine pairs. It is explained 5 as, ”The replacement of the pair A-T by G-C is evidently thermodynamically favourable, since G is bound to C more strongly than is A to T. If it were for thermodynamics alone, the relative G-C content in DNA should have increased during evolution. This is not the case in actuality- in higher organism the G-C content is stabilized at 40-45 percent level”. Further the genomes of higher organism have regions 6-11, the so called putative isochors with of G-C content varying from 30 to 60 percent. Apparently human genome is losing 9 its G-C rich regions.
However irreverent it may appear, I am of the opinion that the genomic processes of natural as well as synthetic genomes have primacy over cell processes and DNA/ genomes are not only self assembling and self replicating but also are self programmable which make them work as mysterious, intricate machines.
1. Daniel G. Gibson, et al, Creation of a Bacterial Cell Controlled by a Chemically Synthesized Genome, / http://www.sciencexpress.org / 20 May 2010 / Page 1 / 10.1126/science. 1190719.
2. Wald, G. The origin of life, in Molecules to Living Cells, W.H. Freeman and company, San Francisco, 1980.
3. Philip C. Hanawalt, Simple inorganic molecules to free- living cells, in Molecules to Living Cells, W.H. Freeman and company, San Francisco, 1980.
5. Volkenshtein, MV, biophysics, Mir Publishers, Moscow, 1983. Page 302.
6. Galtier, N., Piganeau, G., Mouchiround, D., and Duret, L., GC-content Evolution in Mammalian Genomes : The Biased Gene conversion Hypothesis, Genetics. 2001, 159: 907-911.
7. Bernardi, G., et al, The mosaic genome of warm blooded vertebrates, Science, 1985, 228: 953-958. cf (6).
8. Bernardi, G., Isochores and the evolutionary genomics of vertebrates, Gene, 2000, 241: 3-17. cf (6).
9. Arndt, P.F., Hwa, T., Petrov, D.A., Substantial Regional Variation in Substitution Rates in the Human Genome : Importance of GC content, Gene Density, and Telomere-Specific Effects, J. Mol. Evol. 2005, 60 : 748-763.
10. Cohen, N., Dagan, T., Lewistone and Graur, D., GC-composition of the Human Genome :In search of Isochors, Mol. Biol. Evol. 2005, 25 (5): 1260-1272.
11. Meunier, J., and Laurent Duret, L., Recombination Drives the Evolution of GC-content in Human Genome, Mol. Biol. Evol. 2004, 21 (6): 984-990.