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Idealized model (insight ii) of a B-DNA duplex (5′-TCTIApAGITCTATTCT-3′ and complement) and structures of the molecular constituents. The aromatic stack of DNA bases, shown in gray, blue (Ap), and red (guanine, G), is distinctly visible within the sugar phosphate backbone (green ribbons). The connection of deoxyribose sugar units via phosphate groups at distinct 5′ and 3′ positions imparts the DNA strand with directional asymmetry.
