我想問下鹽基(A,C,T,G)化學分子式

DNA四大天王－A、G、T、C
DNA是很長的分子鏈，由四種鹽基組成，分別是腺嘌呤（A , adenine）、鳥糞嘌呤（G , guanine）、胞嘧啶（C , cytosine）及胸線嘧啶（T , thymine）。每一對鹽基不是 A,T就是G,C。在DNA的兩條鏈結合 時，A必定和T結合，G必定和C結合，其他的組合無法銜接這兩條鎖鏈。因為A和T是 由兩個氫鏈所連結，G和C之間的結合則須有三個氫鍵。在RNA中，胸腺嘧啶（T）則由嘧啶（Uracil，U）所取代
purine
A double-ringed, crystalline organic base, C5H4N4, not known to occur naturally, from which is derived the nitrogen bases adenine and guanine, as well as uric acid as a metabolic end product.
Any of a group of organic compounds structurally related to purine, particularly adenine and guanine, and also caffeine, uric acid, theobromine, and theophylline.A heterocyclic organic compound containing fused pyrimidine and imidazole rings. A number of substituted purine derivatives occur in nature; some, as components of nucleic acids and coenzymes, play vital roles in the genetic and metabolic processes of all living organisms.

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pyrimidine
A single-ringed, crystalline organic base, C4H4N2, that forms uracil, cytosine, or thymine and is the parent compound of many drugs, including the barbiturates.
A heterocyclic organic compound containing nitrogen atoms at positions 1 and 3. Naturally occurring derivatives of the parent compound are of considerable biological importance as components of nucleic acids and coenzymes and, in addition, synthetic members of this group have found use as pharmaceuticals.

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adenine
7H-purin-6-amine
A purine base, C5H5N5, that is the constituent involved in base pairing with thymine in DNA and with uracil in RNA.

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圖片參考：http://content.answers.com/main/content/wp/en-commons/thumb/5/51/116px-Adenine_chemical_structure.png


guanine
2-amino-1H-purin-6(9H)-one
2-amino-6-oxo-purine
A purine base, C5H5ON5, that is an essential constituent of both RNA and DNA.

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圖片參考：http://content.answers.com/main/content/wp/en-commons/thumb/1/10/200px-Guanine_chemical_structure.png


cytosine
4-amino-3H-pyrimidin-2-one
A pyrimidine base, C4H5N3O, that is the constituent of DNA and RNA involved in base pairing with guanine.

圖片參考：http://content.answers.com/main/content/img/McGrawHill/Encyclopedia/images/CE558900SX0030.gif


圖片參考：http://content.answers.com/main/content/wp/en-commons/thumb/d/d7/120px-Cytosine_chemical_structure.png


thymine
5-Methylpyrimidine-2,4(1H,3H)-dione
A pyrimidine base, C5H6N2O2, that is an essential constituent of DNA.

圖片參考：http://content.answers.com/main/content/img/McGrawHill/Encyclopedia/images/CE558900SX0040.gif


圖片參考：http://content.answers.com/main/content/wp/en/thumb/c/cd/200px-Thymine.png


uracil
Pyrimidine-2,4(1H,3H)-dione
2,4-dihydroxypryimidine
A pyrimidine base, C4H4N2O2, that is an essential constituent of RNA.

圖片參考：http://content.answers.com/main/content/img/McGrawHill/Encyclopedia/images/CE558900SX0020.gif


圖片參考：http://content.answers.com/main/content/wp/en-commons/thumb/2/2e/102px-Uracil_chemical_structure.png

I hope this can help your understanding. :)