Sugars prebiotic systems

In virtually all experiments that simulate the synthesis of a primordial soup, enantiomers of amino acids and sugars do not occur instead only racemates have been produced (Miller 1953). It is difficult to imagine how only one of the enantiomers formed under the conditions of a primordial broth. Instead, import and identification of biologically relevant molecules in meteorites and comets appears as a more straightforward path. The compounds found in a meteorite provide a natural record of prebiotic chemistry in the early solar system and is closest to the onset of life. 

The possibility that small organic molecules could catalyze organic transformations in a stereoselective way can even be considered as a key element in the origins of life, as it is widely accepted that the source of homochirality in biological systems should be attributed to the presence of enantiomerically enriched a-amino acids in meteorites, and especially once it was demonstrated that these a-amino acids were able to catalyze aldol reactions in a stereoselective way under prebiotic conditions conducing to sugar-type products. ... 

The above example shows how a far-from-equilibrium chemical system can generate and maintain chiral asymmetry, but it only provides a general framework in which we must seek the origins of biomolecular handedness. The origin of biomolecular handedness, or life s homochirality, remains to be explained [11, 12]. Here we shall confine our discussion to how the theory of nonequilibrium symmetry breaking contributes to this important topic. We cannot yet say with confidence whether chiral asymmetry arose in a prebiotic (i.e. before life) process and facilitated the evolution of life, or whether some primitive form of life that incorporated both L- and D-amino acids arose first and subsequent evolution of this life form led to the homochirality of L-amino acids and D-sugars. Both views have their proponents. 

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