The origin of life is one of the unsolved fundamental mysteries in modern natural science. The endeavour to discover some of its secrets continues to challenge researchers from many different scientific domains such as astrophysics and planetary sciences, geology, mineralogy, geochemistry, organic, inorganic, analytical, and physical chemistry, biophysics, biochemistry, biology, and even mathematics. Not to forget the profound interest of philosophers, writers, theologians, and artists in a wide spectrum of aspects on the scientific basics of our origin. How could life originate? In spite of the lack of the whole process, some clear-cut steps in the evolutionary origin of life seem to be established and common sense, today.
We assume, in brief, that before biological evolution more than 3.5 billion years ago defined phases of chemical evolution started with the synthesis of simple pre-biotic organic molecules, such as amino acids, either on Earth or in interstellar environments. Subsequent prebiotic reactions are assumed to require liquid water to form the first polymers. After the molecular selection of a self-replicating system and the so-called RNA-world scenario (Gilbert 1986; Joyce 2002) the DNA-protein-world led via the last universal common ancestor1 to the starting point of biological evolution.
Despite this knowledge, we are far from a coherent understanding of the life-originating phases chronologically separated into cosmic, chemical, and biological evolution. It is, in particular, the incapability to link chemical and biological evolution that continues to puzzle scientists. How can a mix of non-living chemicals be transformed into something as complex as the living cell? Is there some intrinsic aspect of the structure of the involved molecules such as amino acids that will enable us to conclude whether their origin was biological or chemical? Were they active precursors of living structures or "junk" molecules not used up by evolutionary
1 The last universal common ancestor (LUCA) is the first living organism from which all currently living organisms, including Archaeans, Eukaryotes, and Bacteria, descended (Woese 1998). Tracing the phylogenetic tree backwards by ribosomal RNA sequence comparisons derives its hypothetical nature.
U. Meierhenrich, Amino Acids and the Asymmetry of Life. Advances in Astrobiology and Biogeophysics, © Springer-Verlag Berlin Heidelberg 2008
processes? The answer is "yes", each amino acid bears a fingerprint inside itself telling us the story of its origin. This fingerprint is carried and manifested by the chirality of the amino acid.
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