Claim CB030:
Complex organic molecules, such as the bases in RNA, are very fragile and
unstable, except at low temperatures. They would not hold together long
enough to serve as the first self-replicating proto-life.
Source:
Response:
- The source Bergman cites for the fragility of RNA bases (Levy and
Miller 1998) disputes abiogenesis only at high temperatures, around 100
degrees Celsius. They also conclude, "At 0 degrees C, A, U, G, and T
appear to be sufficiently stable (t1/2 greater than or equal
to 106 yr) to be involved in a low-temperature origin of life."
They
also say that cytosine is unstable enough at 0 degrees Celsius (half
life of 17,000 years) that it may not have been involved in the first
genetic material. The discovery of a ribozyme without C-G bases shows
that genetic material without cytosine is plausible (Reader and Joyce
2002).
- If synthesis of nucleo-bases is catalyzed and hydrolysis is not, we
expect the nucleo-bases to accumulate. Formamide, which can form under
prebiotic conditions, has been found to catalyze the formation of
nucleo-bases (Saladino et al. 2001; Saladino et al. 2003).
RNA degrades quickly today because there are enzymes (RNAses) to chew
it up. Those enzymes would not have evolved if RNA degraded quickly on
its own. If complex organic molecules were so fragile, life itself
would be impossible. In fact, life exists even in boiling temperatures
or at very high acidity.
- Life need not have begun with highly stable molecules. Eigen and
Schuster developed a notion of chemical hypercycles, in which many
chemical components coexist; each component of the reaction leads to
other components, which eventually reform the original one (Eigen and
Schuster 1977). Chemicals involved in such a cycle need not persist
longer than the duration of the hypercycle itself.
- Organic molecules may have grown in association with stabilizing
templates, such as clay templates (Ertem and Ferris 1996), or parts of
the hypercycles mentioned above.
References:
- Eigen, M. and P. Schuster. 1977. The hypercycle. A principle of natural
self-organization. Part A: Emergence of the hypercycle.
Naturwissenschaften 64(11): 541-565.
- Ertem, G. and J. P. Ferris. 1996. Synthesis of RNA oligomers on
heterogeneous templates. Nature 379: 238-240.
- Levy, Matthew and Stanley L. Miller. 1998. The stability of the RNA
bases: Implications for the origin of life. Proceedings of the National
Academy of Science USA 95: 7933-7938.
- Reader, J. S. and G. F. Joyce. 2002. A ribozyme composed of only two
different nucleotides. Nature 420: 841-844.
- Saladino, R., C. Crestini, G. Costanzo, R. Negri and E. Di Mauro. 2001. A
possible prebiotic synthesis of purine, adenine, cytosine, and
4(3H)-pyrimidinone from formamide: Implications for the origin of life.
Bioorganic and Medicinal Chemistry 9(5): 1249-1253.
- Saladino, R., U. Ciambecchini, C. Crestini, G. Costanzo, R. Negri
and E. Di Mauro. 2003. One-pot TiO2-catalyzed synthesis of
nucleic bases and acyclonucleosides from formamide: Implications for
the origin of life. ChemBioChem 4(6): 514-521.
created 2003-7-10, modified 2003-7-17