Some molecules can exist in two mirror-image forms, similar to our hands. Although such so-called enantiomers have almost identical physical properties, they are not the same. The fact that they behave to each other like image and mirror image is called chirality (from the Greek “cheiro” for hand). In nature, however, often only one enantiomer exists, for example in amino acids, DNA or sugars. The enzymes that produce these molecules are themselves chiral and therefore only produce one type of enantiomer.
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Source: Phys.org