DNA has two linear polynucleotide strands hydrogen-bonded together to form twisted ladder shape {double helix}|.
hydrogen bonds
Nitrogenous bases adenine and thymine in DNA or uracil in RNA can link by two hydrogen bonds, on aromatic-ring side away from pentose and phosphate, if aromatic-ring planes are parallel, with one inverted. Nitrogenous bases cytosine and guanine can link by three hydrogen bonds, on aromatic-ring side away from pentose and phosphate, if aromatic-ring planes are parallel, with one inverted.
ladder
Strands are pentose sugars and phosphodiester bonds and make ladder sides. Strand bonds have opposite direction. Nitrogenous-base and hydrogen-bond-link planar aromatic rings are ladder rungs. Because tetrahedral chemical bonds form at angle, ladder twists and is helical.
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5-Chemistry-Biochemistry-Nucleic Acid-Configuration
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Date Modified: 2022.0224