Chemistry
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Deoxyribonucleic acid, or DNA, is a long molecule essential for and instrumental in the passing on and preservation of life and genetics. It is usually in the form of a double helix formed by pairs of the four nucleic bases: cytosine [C], guanine [G], adenine [A], and thymine [T]. Cytosine can only pair with guanine and adenine can only pair with thymine.

Bases[]

The four bases of deoxyribonucleic acid can be split up into the purines and the pyrimidines. Pyrimidines are pyrimidine derivative, where pyrimidine is a benzene molecule with a carbon and another carbon meta relative to the first carbon replaced with nitrogen atoms. Purines are a bicyclic pyrimidine, where pyrimidine has been fused with imidazole (basically pyrimidine but with a pentagon instead of a hexagon).

The structure of all four molecules can be seen in the gallery.

Gallery[]

DNA I

The double helix of DNA is composed of short and long sections, not equally spaced sections as incorrectly depicted in many models. This is because the sugar-phosphate backbones of the molecule are not 'perfectly' out of phase with eachother.

Pyrimidine

One of the two resonance structures of pyrimidine.

Pyrimidines

Cytosine is a pyrimidine with an amino and carbonyl group at the 2,4 carbon positions respectively while thymine has two carbonyl groups at the 2,4 position and a methyl group at 5.

Purines

Guanine is adenine with an amino group swapped with carbonyl, a hydrogen swapped with an amino group, and an extra hydrogen. Note the closeness to xanthine, itself only being three methyl groups away from 1,3,7-trimethylxanthine, or caffeine.

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