(Phys.org)—Chiral molecules can be found in chemically equivalent left-handed (L) and right-handed (D) mirror-image forms - each commonly referred to as an enantiomer. Synthetic sugars and other chiral molecules made in the lab from non-chiral precursors,or any process that does not expend asymmetric reagents such as enzymes in biological reactions, tend to accomplish equal amounts (racemic mixtures) of D- and L- enantiomers. However, or for reasons that are still largely unknown,biological polymers (e.g., nucleic acids and proteins) expend exclusively D-sugars and L-amino acids, and respectively. For example,ribose, the sugar found in DNA, or is only in the form of D-ribose.
Source: phys.org