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核碱基

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核碱基(英语:Nucleobase)是指含氮碱基(nitrogenous base),在生物学上通常简单地称之碱基(base)。是在DNARNA中,起配对作用的部分。核碱基都是杂环化合物,其原子位于环上或取代氨基上,其中一部分(取代氨基,以及嘌呤环的1位氮、嘧啶环的3位氮)直接参与碱基配对。

常见的核碱基共有5种:胞嘧啶(缩写C)、鸟嘌呤(G)、腺嘌呤(A)、胸腺嘧啶(T,通常为DNA专有)和尿嘧啶(U,通常为RNA专有)。腺嘌呤和鸟嘌呤属于嘌呤族(缩写作R),它们具有双环结构。胞嘧啶、尿嘧啶、胸腺嘧啶属于嘧啶族(Y),它们的环系是一个六元杂环。RNA中,尿嘧啶取代了胸腺嘧啶的位置。胸腺嘧啶比尿嘧啶多一个5位甲基,这个甲基增大了遗传的准确性。

核碱基有酮式和烯醇式,可以互相转换。在生理pH条件下一般为酮式。[1]

核碱基通过糖苷键核糖脱氧核糖的1位原子相连而形成的化合物叫核苷。核苷再与磷酸结合就形成核苷酸,磷酸基接在五碳糖的5位碳原子上。

主要碱基与核苷结构

核碱基
Chemical structure of adenine

腺嘌呤
Chemical structure of guanine

鸟嘌呤
Chemical structure of thymine

胸腺嘧啶
Chemical structure of cytosine

胞嘧啶
Chemical structure of uracil

尿嘧啶
核苷

Chemical structure of adenosine

腺苷
A
Chemical structure of guanosine

鸟苷
G
Chemical structure of thymidine

胸苷
T
Chemical structure of cytidine

胞苷
C
Chemical structure of uridine

尿苷
U

简拼碱基符号

符号 代替碱基
R A/G
Y C/T
M A/C
K G/T
S G/C
W A/T
H A/T/C
B G/T/C
V G/A/C
D G/A/T
N A/G/C/T

中间产物

核碱基
Chemical structure of hypoxanthine

次黄嘌呤
Chemical structure of xanthine

黄嘌呤
Chemical structure of 7-methylguanine

7-甲基鸟嘌呤
Chemical structure of dihydrouracil

5,6-二氢尿嘧啶
核苷

Chemical structure of inosine

次黄苷
I
Chemical structure of xanthosine

黄苷
X
Chemical structure of 7-methylguanosine

7-甲基鸟苷
m7G
Chemical structure of dihydrouridine

二氢尿苷
D

新四大碱基

近几年有人将表观遗传学修饰的5-甲基胞嘧啶(5mC)称为第5种碱基,5-羟甲基胞嘧啶(5hmC)称为第6种碱基。2011年研究人员发现了第7种DNA碱基“5-甲酰基胞嘧啶”(5fC),和第8种“5-羧基胞嘧啶”(5caC)。这几种碱基实际上都是由胞嘧啶经由Tet蛋白修饰后形成。人类和小鼠干细胞都拥有Tet蛋白,Tet蛋白是重新编程已经分化的细胞的一种重要功能蛋白[2]

参看

外部链接

参考文献

  1. ^ Yang, Jianxiong, 1954-; 杨建雄, 1954-. Fen zi sheng wu xue. 分子生物学(第二版) Di er ban. Beijing Shi. ISBN 7-03-045212-7. OCLC 950961809. 
  2. ^ S, Shen, L, Dai Q.; Wu SC, Collins LB, Swenberg JA, He C, Zhang Y. Tet proteins can convert 5-methylcytosine to 5-formylcytosine and 5-carboxylcytosine. Science. 2011 Sep 2;333(6047):1300-3. Epub 2011 Jul 21. 
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核碱基
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