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An English chemist may have found the hidden gateway to the RNA world, according to an article by Nicholas Wade in the NY Times. This world is the chemical milieu from which the first forms of life are thought to have emerged on earth, perhaps 3.8 billion years ago.
For 20 years researchers have been thwarted as they tried to understand the origin of life. The question was how nuceotides, the building blocks of RNA, could have spontaneously assembled themselves in the primitive earth’s conditions.
If correct, this finding will set researchers on track to solving many other mysteries about the origin of life.
But it also means that for the first time, a plausible explanation exists for how an information-carrying biological molecule could have emerged through natural processes from chemicals on the primitive earth.
In an interview, John D Sutherland of the University of Manchester, says that whether they have “solved” the problem is still an open question. But many peers feel that he has made a major advance in pre-biotic chemistry, which studies the natural chemical reactions that preceded the first living cells.
Scientists had long suspected that the first forms of life carried their biological information not in DNA but in RNA, which is its close chemical cousin. But for 20 years, they could find no plausible way in which nuceotides could have been assembled.
A nucleotide consists of
- a chemical base,
- a sugar molecule called ribose
- and a phosphate group.
Chemists had no difficulty finding plausible natural ways for the constituents to form from natural chemicals. The problem was that there appeared to be no natural way for them all to join together.
According to Gerald F Joyce and Leslie E Orgel, researchers writing in 1999, the spontaneous appearance of nucleotides “would have been a major miracle.”
But the miracle now seems to have been explained. Dr Sutherland says in the journal Nature that he and colleagues Matthew W Powner and Beatrice Gerland have take the same starting chemical used by others unsuccessfully and made them react in an order and in combinations different from those of previous experiments.
They discovered their counterintutive recipe after 10 years of working through every possible combination of plausible chemicals.
They found the starting chemicals will naturally form a compound that is half-sugar and half-base. When another half-sugar and half-base are added, the RNA nucleotide called ribocytidine phosphate emerges.
A second nucleotide is created if ultraviolet light is shone on the mixture.
Dr Sutherland says that he has not yet found natural ways to generate the two other types of nucleotides found in RNA molecules, but synthesis of the first two was thought to be the harder puzzle.
If all four nucleotides form naturally, they then zip together easily to form an RNA molecule with a backbone of alternating sugar and phosphate groups.
The bases attached to the sugar constitute a four-letter alphabet in which biological information can be representation.
Says Sutherland: “My assumption is that we are here on this planet as a fundamental consequence of organic chemistry. So it must be chemistry that wants to work.”
Dr Joyce, who is an expert on the chemical origin of life at the Scripps Research Institute in San Diego, says “The chemistry is very robust: all the yields are good, and the chemistry is simple.”
It is phosphate that plays a critical role not only as an ingredient but also as a catalyst and in regulating acidity, according to Dr Sutherland’s reconstruction.
He says he was so impressed by the role of phosphate that “this makes me think of myself not as a carbon-based life form but as a phosphate-based life form.”
If Sutherland’s proposal is correct, it will set conditions that should help solve the many other problems in reconstructing the origin of life.
In a famous letter to Joseph Hooker in 1871, Charles Darwin wrote that life probably began “in some warm little pond, with all sorts of ammonia and phosphoric salts.”
Sutherland’s report supports Darwin. His proposed chemical reactions take place at moderate temperatures, though one does best at 60 degrees Celsius.
“It’s consistent with a warm pond evaporating as the sun comes out,” he says.
sole source: Nicholas Wade’s article in the NY Times on 5/14/09. www.nytimes.com
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