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Molecules of biological origin always have a fixed handedness or chirality. For example you only ever see right handed sugars and left handed amino acids in nature. But why?

Credits:

Meteorite image – Art Bromage – https://commons.wikimedia.org/wiki/Fi…
RNA and DNA images – Sponk – https://commons.wikimedia.org/wiki/Fi…
Viking lander video – MASA[…]