Study Builds On Plausible Scenario for Origin of Life On Earth

Discussion in 'Science and Nature' started by MelT, Aug 10, 2011.

  1. \t\t\t \t\t\t \t\t\t\tScienceDaily (Aug. 10, 2011) - A relatively simple combination of naturally occurring sugars and amino acids offers a plausible route to the building blocks of life, according to a paper published in Nature Chemistry.

    The study shows how the precursors to RNA could have formed on Earth before any life existed. It was authored by Jason E. Hein, Eric Tse and Donna G. Blackmond, a team of researchers with the Scripps Research Institute. Hein is now a chemistry professor with University of California, Merced.

    Biological molecules, such as RNA and proteins, can exist in either a natural or unnatural form, called enantiomers. By studying the chemical reactions carefully, the research team found that it was possible to generate only the natural form of the necessary RNA precursors by including simple amino acids.

    "These amino acids changed how the reactions work and allowed only the naturally occurring RNA precursors to be generated in a stable form," said Hein. "In the end, we showed that an amazingly simple result emerged from some very complex and interconnected chemistry."

    The natural enantiomer of the RNA precursor molecules formed a crystal structure visible to the naked eye. The crystals are stable and avoid normal chemical breakdown. They can exist until the conditions are right for them to change into RNA.

    The study was led by Blackmond and builds on the work of John D. Sutherland and Matthew W. Powner published in 2009 and covered by outlets such as The New York Times and Wired. Sutherland is a chemist with Cambridge's Medical Research Council Laboratory of Molecular Biology. Powner is a post-doctoral scholar with Harvard University.

    Original release:

    The single-handedness of biological molecules is critical for molecular recognition and replication processes and would seem to be a prerequisite for the origin of life. A drawback of recently reported synthetic routes to RNA is the requirement for enantioenriched reactants, which fails to address the puzzle of how the single chirality of biological molecules arose. Here, we report the synthesis of highly enantioenriched RNA precursor molecules from racemic starting materials, with the molecular asymmetry derived solely from a small initial imbalance of the amino-acid enantiomers present in the reaction mixture. Acting as spectators to the main reaction chemistry, the amino acids orchestrate a sequence of physical and chemical amplification processes. The emergence of molecules of single chirality from complex, multi-component mixtures supports the robustness of this synthesis process under potential prebiotic conditions and provides a plausible explanation for the single-handedness of biological molecules before the emergence of self-replicating informational polymers.
    \t\t\t\t\t\t\t\t \t\t\t\t\t\t\t\t\t\t\t\t \t\t\t\t\t\t\t\t\t\t\t\t\t\t \t\t\t\t\t\t\t\t\t\t\t\t \t\t\t\t\t \t \t\t \tA route to enantiopure RNA precursors from nearly racemic starting materials : Nature Chemistry : Nature Publishing Group
  2. 'Ancestral Eve' Crystal May Explain Origin of Life's Left-Handedness

    \t\t\t \t\t\t \t\t\t\tScienceDaily (Apr. 21, 2010) - Scientists are reporting discovery of what may be the "ancestral Eve" crystal that billions of years ago gave life on Earth its curious and exclusive preference for so-called left-handed amino acids. Those building blocks of proteins come in two forms -- left- and right-handed -- that mirror each other like a pair of hands.

    Their study, which may help resolve one of the most perplexing mysteries about the origin of life, is in ACS' Crystal Growth & Design, a bi-monthly journal.
    Tu Lee and Yu Kun Lin point out that conditions on the primordial Earth held an equal chance of forming the same amounts of left-handed and right-handed amino acids. Nevertheless, when the first forms of life emerged more than 3 billion years ago, all the amino acids in the proteins had the left-handed configuration. That pattern continued right up to modern plants and animals.

    The scientists used mixtures of both left- and right-handed aspartic acid (an amino acid) in laboratory experiments to see how temperature and other conditions affected formation of crystals of the material. They found that under conditions that could have existed on primitive Earth, left-handed aspartic acid crystals could have formed easily and on a large scale.

    "The aspartic acid crystal would then truly become a single mother crystal: an ancestral Eve for the whole left-handed population," the article notes.

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