Scientists have long known that most compounds in living things exist in mirror-image forms. The two forms are like hands; one is a mirror reflection of the other. They are different, cannot be superimposed, yet identical in their parts.
But amino acids, which are the building blocks of terrestrial proteins, are all ‘left-handed,’ while the sugars of DNA and RNA are ‘right-handed.’ The mystery as to why this is the case, “parallels in many of its queries those that surround the origin of life,” says Sandra Pizzarello, a research professor at Arizona State University.
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