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.
Ribose sugar (RNA) or deoxyribose sugar (DNA), phosphate group, and nitrogenous-base adenine, guanine, cytosine, and thymine in DNA or uracil in RNA can link to other bases with phosphodiester bonds to make sequences {base sequence} {DNA sequence}.
Two adjacent nucleic-acid polymers {anti-parallel strands} can have opposite bond direction.
Hydrogen bonding between adenine and thymine in DNA or uracil in RNA, or between guanine and cytosine {base pairing}, links two DNA strands or DNA and RNA strands.
Hydrogen bonds can form between adenines and thymines in DNA or uracils in RNA, and between cytosines and guanines {complementary bases}.
polymer chain {strand, DNA}.
Topoisomerase and gyrase affect DNA coiling and can add to or subtract from helix angle {supercoiling}. Circular DNA has negative supercoiling.
5-Chemistry-Biochemistry-Nucleic Acid
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Date Modified: 2022.0225