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DNA结构DNA is composed of 2 strands running in opposite directions that are twisted together, also called the double helix. The strands are composed of nucleotides and deoxyribose sugars. A phosphodiester link connects the deoxyribose sugars with each other, and the hydrogen bonds between phosphates cause the DNA strand to twist. The two strands are bound with weak hydrogen bonds between the complementary nucleotides. The nitrogenous bases are “inside” like rungs on a ladder. Adenine binds with thymine and cytosine binds with guanine. The visualisation of the structure is presented on the figure 1.

Two grey bands, representing sugar-phosphate chains, are twisted in vertically aligned double helix, each band going toward opposite directions - up or down. Between them, connected, horizontal pair bases are shown as tubes in four different colours and lengths. The diameter of the helix is shown to have 2 nanometers, the complete turn of the helix is shown to have 3.4 nanometers, and space between two base couples is shown to have 0.34 nanometers.

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