Deoxyribonucleic acid chirality

Liquid Crystalline Structures. In certain ceUular organeUes, deoxyribonucleic acid (DNA) occurs in a concentrated form. Striking similarities between the optical properties derived from the underlying supramolecular organization of the concentrated DNA phases and those observed in chiral nematic textures have been described (36). Concentrated aqueous solutions of nucleic acids exhibit a chiral nematic texture in vitro (29,37). 

Ever since the beginning of life on primitive Earth, biopolymers and biomolecules have essentially comprised optically active constituents because of the natural selection of Z-amino acids and tZ-sugars. Although the origin of this biomolecular handedness is a long debated issue among biologists, chemists, physicists, and astronomers,1 5 it is accepted that our life is a consequence of the chemistry of homochiral biosubstances. Deoxyribonucleic acid (DNA) is a classic example of a chiral biopolymer. Its chirality is essentially characterized... 

Double bond, 14, 38-40, 170-172 Double helix, 1094—1096. See also Deoxyribonucleic acid Drugs. See also AIDS Antibiotics chiral, 273 generic names of, 63 Dyes, 896-897... 

In principle, polymers consisting of a single kind of chiral monomeric unit can produce left- and right-handed helices. But the two kinds of helix are diastereomeric to each other that is, they are not energetically equal. For this reason, either left or right-handedness is a preferred form for such polymers. For example, polymers of chiral (S)-a-olefins and most poly(D-saccharides) form exclusively left-handed helices. On the other hand, deoxyribonucleic acids and almost all poly(L-a-amino acids) occur as right-handed helices. Polymers of the corresponding monomer antipodes form helices of opposite turn. 

Figure 1.4. Chiral supramolecular structures (a) a-helix of polypeptides, (b) poly-prolin-helix of collagene, and (c) deoxyribonucleic acid (DNA) Z = D-Deoxyribose, P = phosphoric acid, A — adenine, G = guanine, C = cytosine, T = thymine (from [8]).

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