DNA模型_精品文档.docx

1、Molecularstructureofnucleicacids核酸分子结构Astructurefor Deoxyribosenucleicacid脱氧核糖核酸的结构Wewishtosuggestastructureforthesaltofdeoxyribosenucleicacid(D.N.A).Thisstructurehasnovelfeatureswhichareofconsiderablebiologicalinterest.我们希望去提出一种结构是刺激性的脱氧核糖核酸即DNA。这个结构有一些新的特征对于生物学有很多重要的意义。Astructurefornucleicacidhasa

2、lreadybeenproposedbyPaulingandCorey.鲍林和科瑞 提出了核酸的结构。Theykindlymadetheirmanuscriptavailabletousinadvanceofpublication.在出版前，他们善良地把对他们有用的手稿给我们。Theirmodelconsistsofthreeintertwinedchains,withthephosphatesnearthefibreaxis,andthebasesontheoutside.他们的模型由三个缠绕的链组成，以磷酸盐靠近纤维轴线并且盘绕在外部。Inouropinion,thisstructurei

3、sunsatisfactoryfortworeasons:在我们看来，这个架构不够完善在于两个原因(1)WebelievethatthematerialwhichgivestheX-raydiagramsisthesalt,notthefreeacid,withouttheacidichydrogenatomsitisnotclearwhatforceswouldholdthestructuretogether,especiallyasthenegativelychargedphosphatesneartheaxiswillrepeleachother.(2)someofthewanderwa

4、alsdistancesappeartobetoosmall.（1）我们相信这种材料在X射线钠盐环境下，不是游离的酸，没有酸性氢原子，不清楚是什么力量将它们的结构结合在一起，尤其是靠近轴的负的带负电的磷酸盐互相排斥的现象。（2）一些范德华力距离看起来很小。 Another three-chain structure has also been suggested by Fraser (in the press).IN his model the phosphates are on the outside and the bases on the inside, linked together

5、by hydrogen bonds. This structure as described is rather ill-defined, and for this reason we shall not comment on it. 另一个三条链的结构被费斯提出并即将出版。在他的提出的模型中磷酸盐在外部的与在内部的通过氧氢键共同连接组成。这个结构也被描述为有些不明确，因为这个原因我们没有对它提出意见。Wewishtoputforwardaradicallydifferentstructureforthesaltofdeoxyribosenucleicacid.Thisstructurehas

6、twohelicalchainseachcoiledroundthesameaxis (seediagram).我们希望提出了一个结构与脱氧核糖核酸结构本质不同的结构。这个结构有两个螺旋形的链，每一个盘绕着相同的轴（看图表）（查看时请拉大）Wehavemadetheusualchemicalassumptions.namely,thateachchainconsistsofphosphatedie-stergroupsjoining-D-deoxyribofuranoseresidueswith3,5linkages.我们做出了不同寻常的化学设想，也就是每一条链由-D脱氧核糖的3,5磷酸二酯键

7、和碱基形成。Thetwochains(butnottheirbases) arerelatedbyadyadperpendiculartothefibre axis. 这两条链（不是它们的碱基）通过一对垂直相交的纤维轴线相联系。Bothchainsfollowrighthandedhelices,butowingtothedyadthesequencesoftheatomsinthetwochainsruninoppositedirections.两条链根据右手螺旋，但是应该由于两条链中的原子序列处于相反方向。EachchainlooselyresemblesFurbergs2modelNo.

8、1;thatis,thebasesareontheinsideofthehelixandthephosphatesontheoutside.每一条链大体上类似于富尔贝里提出的第一模型，也就是说，碱基在内部磷酸盐在外部。TheconfigurationofthesugarandtheatomsnearitisclosetoFurbergsstandardconfiguration,thesugarbeingroughlyperpendiculartotheattachedbase.糖的结构和靠近的原子与富尔贝里提出的模型标准结构相类似，糖大体上垂直于附着的碱基。Thereisaresidueon

9、eachchainevery3.4A.inthez-direction.每一条链在z形方向上3-4A上有残留。We have assumed an angle of 36 between adjacent residues in the same chain, so that the structure repeats after 10 residues on each chain, that is,after 34 A. The distance of a phosphorus atom from the fibre axis is 10 A. As the phosphates are o

10、n the outside, cautions have easy access to them.我们假定同一条链中相邻核苷酸之间呈36度角，结果这个结构便重复在每条链上每10个核苷酸（34A）。磷酸原子与纤维轴距离是10A。因为磷酸在外面，阳离子很容易接触到它们。Thestructureisanopenone,anditswatercontentisratherhigh.Atlowerwatercontentswe wouldexpectthebasestotiltsothatthestructurecouldbecomemorecompact.这是一个开放的结构，它的含水量很高。低一点的含

11、水量我们可以希望碱基倾斜以至于这个结构能够更紧凑。Thenovelfeatureofthestructureisthemannerinwhichthetwochainsareheldtogetherbythepurineanpyrimidinebases.Theplanesofthebasesareperpendiculartothefibreaxis.这种新奇的结构特征是两条链通过嘌呤和嘧啶连接的碱基结合而成的。其中碱基垂直于纤维轴。They are joined together in pairs,a single base from one chain being hydrogen-bo

12、nded to a single base from the other chain,so that the two lie side by side with identical z-co-ordinates. 它们是成对出现的，一条链的一部分碱基被氧化并与另一个链上的碱基结合，两条链肩并肩联系在一起。One of the pair must be a purine and the other a pyrimidine for bonding to occur. 其中之一必须是嘌呤另一个结合嘧啶才能发生一系列反映。 The hydrogen bonds are made as follows

13、: purine position 1 to pyrimidine position 1 ; purine position 6 to pyrimidine position 6.这个氧化结合是：嘌呤位置1与嘧啶位置1；嘌呤位置6与嘧啶位置6。Ifitisassumedthatthebasesonlyoccurinthestructureinthemostplausibletautomericforms(thatis,withtheketoratherthantheenolconfigurations)itisfoundthatonlyspecificpairsofbasescanbondto

14、gether.Thesepairsare:adenine(purine)withthymine(pyrimidine),and guanine(purine)withcytosine(pyrimidine).如果假设碱基仅仅在这个结构中以最合理的互变异构形式存在（也就是说，是氧化而不是烯醇配置），那么只有特殊的碱基对才能结合一起。这些配对是腺嘌呤（嘌呤）和胸腺嘧啶（嘧啶），鸟嘌呤（嘌呤）和胞嘧啶（嘧啶）。 Inotherwords,ifanadenineformsonememberofapair,oneitherchain,thenontheseassumptionstheothermembermustbethymine;similarlyforguanineandcytosine.换句话说，如果一个腺嘌呤作为一对中的成分，那么另一成分必须是胸腺嘧啶，同理，如果是鸟嘌呤则另一部分是胞嘧啶。Thesequenceofbasesonasinglechaindoesnotappeartoberestrictedinanyway.某一链上的碱基序列在单链中不会以任何形式被安排。However,ifonlyspecificpairsofbasescanbe