Origin of Life

Prebiotic Synthesis of Ribose

Ribose is the most troublesome subunit for origin of life theories. It can only be synthesized in small quantities under plausible prebiotic conditions, and its lifetime in water is extremely short (73 minutes at 100 degrees Celsius, and 44 years at 0 degrees Celsius). Given that it is hard to synthesize in large quantities and that it decays rapidly once it is produced, it is difficult to see how a reasonable concentration of ribose ever existed in the soup. Many scientists including Miller have suggested that the first RNA molecules probably did not include ribose (thus the term pre-RNA). ⁷

   Ribose presents another difficulty. Just like amino acids, sugars have isomers (mirror images). It has been found experimentally ^8,9 that these isomers interfere with self replication. The interference is severe because it terminates the growing chain. So when the first living prebiotic RNA tries to replicate, it must do so in an environment enriched in one isomer of ribose. No mechanism for such an enrichment has been proposed by researchers.

   Many scientists have decided that the problems with ribose are so severe that the molecule should be excluded as a possible building block. Since ribose is just the glue that holds RNA together, other chemicals should be able to take its place.⁸

   Finally, ribose is a reducing sugar. This means that it will react very quickly with amino acids, and the resulting polymer will fall out of solution. Any ribose in the soup will quickly be eliminated by reactions with the amino acids in the soup.

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