Desafiando a Nomenklatura Científica: A 'profecia' de Robert Shapiro: em 2011 nós compreenderemos a origem da vida

sexta-feira, janeiro 29, 2010

Falta apenas um anos para vermos se a 'profecia' de Robert Shapiro se cumpre:

Entendermos finalmente sobre a origem da vida.

ROBERT SHAPIRO

Professor Emeritus, Senior Research Scientist, Department of Chemistry, New York University. Author, Planetary Dreams

We shall understand the origin of life within the next 5 years

Two very different groups will find this development dangerous, and for different reasons, but this outcome is best explained at the end of my discussion.

Just over a half century ago, in the spring of 1953, a famous experiment brought enthusiasm and renewed interest to this field. Stanley Miller, mentored by Harold Urey, demonstrated that a mixture of small organic molecules (monomers) could readily be prepared by exposing a mixture of simple gases to an electrical spark. Similar mixtures were found in meteorites, which suggested that organic monomers may be widely distributed in the universe. If the ingredients of life could be made so readily, then why could they not just as easily assort themselves to form cells?

In that same spring, however, another famous paper was published by James Watson and Francis Crick. They demonstrated that the heredity of living organisms was stored in a very large large molecule called DNA. DNA is a polymer, a substance made by stringing many smaller units together, as links are joined to form a long chain.

The clear connection between the structure of DNA and its biological function, and the geometrical beauty of the DNA double helix led many scientists to consider it to be the essence of life itself. One flaw remained, however, to spoil this picture. DNA could store information, but it could not reproduce itself without the assistance of proteins, a different type of polymer. Proteins are also adept at increasing the rate of (catalyzing) many other chemical reactions that are considered necessary for life. The origin of life field became mired in the "chicken-or-the egg" question. Which came first: DNA or proteins? An apparent answer emerged when it was found that another polymer, RNA (a cousin of DNA) could manage both heredity and catalysis. In 1986, Walter Gilbert proposed that life began with an "RNA World." Life started when an RNA molecule that could copy itself was formed, by chance, in a pool of its own building blocks.

Unfortunately, a half century of chemical experiments have demonstrated that nature has no inclination to prepare RNA, or even the building blocks (nucleotides) that must be linked together to form RNA. Nucleotides are not formed in Miller-type spark discharges, nor are they found in meteorites. Skilled chemists have prepared nucleotides in well-equipped laboratories, and linked them to form RNA, but neither chemists nor laboratories were present when life began on the early Earth. The Watson-Crick theory sparked a revolution in molecular biology, but it left the origin-of-life question at an impasse.

Fortunately, an alternative solution to this dilemma has gradually emerged: neither DNA nor RNA nor protein were necessary for the origin of life. Large molecules dominate the processes of life today, but they were not needed to get it started. Monomers themselves have the ability to support heredity and catalysis. The key requirement is that a suitable energy source be available to assist them in the processes of self-organization. A demonstration of the principle involved in the origin of life would require only that a suitable monomer mixture be exposed to an appropriate energy source in a simple apparatus. We could then observe the very first steps in evolution.

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