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运用分子力学方法研究了 3个含溴代胞嘧啶的分子内三螺旋及相应的未溴代分子内三螺旋DNA .理论结果表明 :当分子内三螺旋Hoogsteen嘧啶链的胞嘧啶被溴代胞嘧啶取代后其稳定性最强 ;而当分子内三螺旋 2条嘧啶链的胞嘧啶同时被溴代后 ,其稳定性最差 .从分子力学计算得到 ,4种分子内三螺旋的碱基以C3′ endo糖环构象为主 .在三螺旋YTCY( 2条嘧啶链中的胞嘧啶均被溴代胞嘧啶取代 )中 ,也含有一定数量的C2′ endo糖环构象 .因此 ,分子内三螺旋YTCY是A DNA和B DNA的综合体 ,而其他 3种三螺旋则是典型的A DNA . 相似文献
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Effects of an electromagnetic field on intracellular calcium oscillations in a cell with external noise
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Intracellular calcium ion concentration oscillation in a cell subjected to external noise and irradiated by an electromagnetic field is considered. The effects of the intensity E0, the polar angle θ and the frequency omega of the external electric field on steady-state probability distribution and the mean Ca2+ concentration, respectively, are investigated by a numerical calculation method. The results indicate that (i) variation of ω cannot affect the intracellular calcium oscillation; (ii) the steady-state probability distribution presents a meaningful modification due to the variations of E0 and θ, while variation of θ does not affect the steady-state probability distribution under the condition of a small E0, and E0 cannot affect the steady-state probability distribution either when θ = π/2; (iii) the mean Ca2+ concentration increases as E0 increases when θ < π/2 and, as θ increases, it first increases and then decreases. However, it does not vary with E0 increasing when θ = π/2, but it increases with θ increasing when E0 is small. 相似文献
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Scanningtunnelingmicroscope(STM)hasrecentlybeenappliedtothestudyoftheadsorptionoforganicandbiologicalmoleculesinvariousenvironments,includingliquidcrystal(LC),onsurface.Inparticular,4_n_alkyl4′cyanobiphenyls(mCB,wheremisthenumberofcarbonsinthealkylgroup)on… 相似文献
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Loop环对分子内三螺旋DNA稳定性的影响 总被引:1,自引:0,他引:1
用分子力学方法研究了 4个分子内三螺旋DNA ( 5′ d(TC) 6 d(T) m d(CT) 6 d(C) n d(AG) 6,m ,n分别为 4,3)的稳定性 ,并与相应的分子间三螺旋d(TC) 6 d(AG) 6·d(CT) 6进行了比较 .结果表明 :Loop环对分子内三螺旋的稳定性影响较小 ,但是Loop上碱基和糖环构象的变化依赖于Loop环的长度 .Loop使分子内三螺旋DNA嘌呤链的碱基堆积作用降低 ,链长增加 .三螺旋DNA的糖环构象大部分是S型 ,同时也存在N型以及其他构象 . 相似文献
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本文研究了时间延迟对Logistic系统从亚稳态跃迁到稳定态的跃迁率的影响. 假设在细胞演化过程中细胞衰减存在时间延迟,利用小延迟时间条件下一阶近似方法和最陡下降法导出了系统的跃迁率解析式. 数值计算结果表明,内噪声,外噪声和内外噪声之间的关联促使系统从亚稳态跃迁到稳定态, 而时间延迟阻碍了系统从亚稳态到稳定态的跃迁, 即时间延迟增强了系统亚稳态的稳定性.
关键词:
Logistic模型
跃迁率
时间延迟
噪声 相似文献
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利用吸收光谱和荧光光谱方法,研究了吖啶橙(AO)与质粒DNA水溶液、以及含胶束介质的吖啶橙与质粒DNA溶液体系的相互结合作用及减色效应。结果表明:吖啶橙对质粒DNA的吸收光谱有减色效应;含十二烷基硫酸钠(SDS)的AO水溶液体系中,随着SDS浓度的增加,其光谱结果表现为由凝聚态向单体的转化。而在含十二烷基硫酸钠(SDS)的AO与质粒DNA溶液体系中,吖啶橙凝聚态随SDS浓度的增加,对AO与质粒DNA相互结合产生协同的减色效应,使质粒DNA空间结构发生缩拢。进一步采用电泳法研究了AO凝聚态可能对质粒DNA构象的影响,结果表明:在AO与质粒DNA溶液体系中,AO浓度的增加对质粒DNA构象未产生影响;而在含有SDS的AO与质粒DNA的溶液体系中,由于SDS对AO凝聚态的解聚作用,以及SDS对质粒DNA减色效应的协同作用,使得质粒DNA的构象发生变化,诱导质粒DNA形成超螺旋构象 相似文献
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OligonucleotidecanrecognizethemajorgrooveofdoublehelicalDNAatspecificsequencesbyformingHoogsteenorreverseHoogsteenhydrogenbondswithpurinebasesoftheWatsonCrickbasepairs,resultinginatriplehelix[1].Triplehelixformingoligonucleotidescanbeusedtoselectivelyc… 相似文献
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Conformation stabilities of intramolecular triple-helical DNAs (intra-tnplex DNAs: 5-d(TC)6-d(T)m-d(CT)6-d(C)n-d(AG)6-3',where m and n are chosen to be 4 and 3) have been examined by molecular mechanics.The four intra-triplexes (H-DNAs) are compared with the mtermolecular triplexes d(TC)6 * d ( AG)6 d(CT)6.The results revealed that loops do not significantly influence the mtratriplex conformations,loop conformations,however,depend partly on its length.Loop also makes strand Ⅱ of every intra-triplex DNA longer than that of the inter-triplex DNA.Most of residue sugar conformations of triple-helical DNAs are S-type,there aiso exist,however,N-type conformation and the conformations between S-type and N-type Possible models of the five triplex DNAs are presented. 相似文献
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