But now thus saith the LORD that created thee,
Isaiah 43:1
"Every biologist knows that life depends on homochirality: building blocks arranged with only one hand. ..... proteins are made up of 100% left-handed amino acids, and DNA/RNA chains use 100% right-handed sugars. Scientists know this is “one of the deepest mysteries in chemistry,” as an embedded video clip on Space.com states.
“Scientists do not yet understand how biology came to rely on one handedness and not the other.” (Science Daily)
“.… molecules with the wrong ‘handedness’ won’t work at all in many biological systems. Because of that, most of the important chiral molecules on Earth, like amino acids, are all the same “handedness” as each other. But scientists don’t know how the Earth came to favor particular varieties to start with. (Space.com)
“While homochirality—the use of only one handedness of any given molecule—is evolutionarily advantageous, it is unknown how life chose the molecular handedness seen across the biosphere.” (Caltech)
Indeed, it is very hard for intelligent humans to separate them. Living cells, however, manufacture and select one-handed molecules reliably all the time. Insertion of the wrong hand in a protein or DNA molecule is often destructive, breaking the function of the molecule. In cells, proofreading processes correct the errors or destroy the chains." CEH