The prebiotic role of adenine: A critical analysis
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Adenine plays an essential role in replication in all known living systems today, and is prominent in many other aspects of biochemistry. It occurs among the products of oligomerization of HCN. These circumstances have stimulated the idea that adenine was a component in a replication system that was present at the start of life. Such replicators have included not only RNA, but also a number of simpler RNA-like alternatives which utilize a simpler backbone.
Despite these encouraging indicators, a consideration of the chemical properties of adenine reveals reasons that disfavor its participation in such a role. These properties include the following: (1) Adenine synthesis requires HCN concentrations of at least 0.01 M. Such concentrations would be expected only in unique circumstances on the early Earth. Adenine yields are low in prebiotic simulations, and if a subsequent high-temperature hydrolysis step is omitted, the reported yield does not represent adenine itself, but 8-substituted adenines and other derivatives. (2) Adenine is susceptibile to hydrolysis (the half life for deamination at 37 °C, pH 7, is about 80 years), and to reaction with a variety of simple electrophiles, forming a multiplicity of products. Its accumulation would not be expected over a geological time scale, and its regioselective incorporation into a replicator appears implausible. (3) The adenine-uracil interaction, which involves two hydrogen bonds (rather than three, as in guanine-cytosine pairing) is weak and nonspecific. Pairing of adenine with many other partners has been observed with monomers, synthetic oligonucleotides and in RNA. The hydrogen-bonding properties of adenine appear inadequate for it to function in any specific recognition scheme under the chaotic conditions of a prebiotic soup.
New and fundamental discoveries in the chemistry of adenine would be needed to reverse this perception. An alternative and attractive possibility is that some other replicator preceeded RNA (or RNA-like substances) in the origin of life.
KeywordsAdenine Uracil Geological Time Scale Prebiotic Synthesis Prebiotic Condition
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- Cairns-Smith, A.G.: 1982,Genetic Takeover and the Mineral Origins of Life, Cambridge Univ. Press, Cambridge, U.K.Google Scholar
- Cronin, J.S., Pizzarello, S. and Cruikshank, D.P.: 1988, inMeteorites and the Early Solar System, Kerridge, J.F. and Matthews, M.S., eds., Univ. of Arizona Press, Tucson, 819–857.Google Scholar
- Dunn, D.B. and Hall, R. H.: 1975, InHandbook of Biochemistry and Molecular Biology, 3rd Edition, Fasman, G.D., ed., CRC Press, Cleveland, 76.Google Scholar
- Ferris, J.P.: 1984, Chemical and Engineering News, August 1984, p 22.Google Scholar
- Giner-Sorolla, A. and Oró, J.: 1993, Abstracts 7th ISSOL Meeting, 10th International Conference on the Origin of Life, Barcelona, 45.Google Scholar
- Hayatsu, R. and Anders, E.: 1981,Topics Curr. Chem. 99, 37.Google Scholar
- Jones, A.S., Mian, A.M. and Walker, R.T.: 1966, J. Chem. Soc. C, 692.Google Scholar
- Joyce, G.F. and Orgel, L.E.: 1993, InThe RNA World, Gesteland, R.F. and Atkins, J.F., eds., Cold Spring Harbor Laboratory Press, Plainview, N.Y., 1.Google Scholar
- Kochetkov, N.K. and Budovskii, E.I.: 1971,Organic Chemistry of Nucleic Acids, Parts A and B, Plenum, New York.Google Scholar
- Lister, J.H.: 1971,Fused Pyrimidines, Part II, Purines, Wiley Interscience, New York.Google Scholar
- Mian, A.M. and Walker, R.T.: 1968, J. Chem. Soc. C, 2577Google Scholar
- Miller, S.L. and Orgel, L.E.: 1973,The Origins of Life on the Earth, Prentice Hall, Englewood Cliffs, N.J.Google Scholar
- Schwartz, A.W. and Orgel L.E.: 1985,Science 228, 185.Google Scholar
- Shapiro, R.: 1981, InChromosome Damage and Repair, Seeberg, E. and Kleppe, K., eds., Plenum Press, New York, 565–570.Google Scholar
- Shapiro, R.: 1986,Origins: A Skeptic's Guide to the Creation of Life on Earth, Summit, New York.Google Scholar
- Stryer, L.: 1988,Biochemistry, Third Edition, W.H. Freeman, New York, 82.Google Scholar
- Watson, J.D., Hopkins, N.H., Roberts, J.W., Steitz, J.A. and Weiner, A.M.: 1987,Molecular Biology of the Gene, Fourth Ed., Vol. II, Benjamin/Cummings, Menlo Park, CA., 1104.Google Scholar