Taken from: https://www.cfa.harvard.edu/~ejchaisson/cosmic_evolution/docs/fr_1/fr_1_chem4.html A central puzzle in modern biochemistry is life’s chirality—that is, a tendency for life’s molecules to have a certain preferential orientation, or “handedness.” Much of life is said to be inherently left-handed, especially its amino acids. No one has ever been able to explain satisfactorily how life became so asymmetric. Yet broken symmetry seems as central to biology and life on Earth as it is to physics and matter in the early Universe. Asymmetry may well be an essential prerequisite for the origin and evolution of complexity throughout all of Nature. Many molecules display two kinds of structures that are mirror images of each other. Their chemical formulas are the same in both cases, but the orientations of some of the molecules’ atoms are reversed left for right and right for left. For example, as shown in Figure 5.13, two forms of the alanine amino acid are possible; each is a mirror image of the other, much like our left and right hands are mirror images, as are the left- and right-handed wood screws also shown in the figure. FIGURE 5.13 FIGURE 5.13 — Left-handed and right-handed screws (top) are in some ways analogous to the mirror-image arrangements of the atoms in simple molecules, such as those of the alanine amino acid shown here (bottom). In life as we know it, however, such molecules are constructed only in their left-handed configurations.
section snipped by mod, owing to copyright. See the link
The part that got me interested was:
Life’s amino-acid preference for left-handedness is particularly puzzling because such molecules, when artificially produced in the laboratory, invariably show an equal mixture of left- and right-handed configurations. (meaning we can't make just left or just right in the lab) Lamron333 Furthermore, should a right-handed amino acid drift into a living organism, the catalysts that control protein production will quickly destroy it. Not only that, when a living organism dies and decays, thermal fluctuations change molecular shapes randomly, so that eventually an even left-right mixture results. Why terrestrial life employs only left-handed amino acids or right-handed nucleic acids is one of the great unsolved mysteries of chemical evolution.
Any Thoughts?
