生物分子介电常数计算初探

目前已知的部分生物大分子的介电常数基本都是由实验加以测定的。本文对DNA等生物分子的介电常数进行了理论计算。得出与实验结果较为接近的结论。且较园满地介释了DNA分子在生物体内的功能     

生物分子介电常数计算初探

目前已知的部分生物大分子的介电常数基本都是由实验加以测定的。本文对DNA等生物分子的介电常数进行了理论计算。得出与实验结果较为接近的结论。且较园满地介释了DNA分子在生物体内的功能     

Selfish genes, the phenotype paradigm and genome evolution

Natural selection operating within genomes will inevitably result in the appearance of DNAs with no phenotypic expression whose only 'function' is survival within genomes. Prokaryotic transposable elements and eukaryotic middle-repetitive sequences can be seen as such DNA's and thus no phenotypic or evolutionary function need be assigned to them.     

Quiet debut for the double helix

Past discoveries usually become aggrandized in retrospect, especially at jubilee celebrations, and the double helix is no exception. The historical record reveals a muted response by the scientific community to the proposal of this structure in 1953. Indeed, it was only when the outlines appeared of a mechanism for DNA's involvement in protein synthesis that the biochemical community began to take a serious interest in the structure.     

DNA弹性杆力学分析的保结构算法和图形后处理

基于Kirchhoff动力学比拟技巧，以弹性杆中心线弧长为拟时间变量，建立了DNA弹性杆结构模型。DNA弹性杆的超细长特性要求长时间数值模拟，探讨了利用辛算法对DNA弹性杆模型长时间计算的问题，给出了相应的算法和数值仿真结果。利用Kirchhoff弹性杆模型的比拟技巧，建立了描述DNA弹性杆曲面的微分／积分方程组，给出了曲面方程的数值解法和DNA弹性杆图形后处理的计算实例和分析。     

稀土生物效应机理研究进展

就稀土离子对DNA结构的影响,对DNA、PNA水解的影响,人工糖核酸酶的初步合成,稀土螯 合物的生物探针这四个方面论述了近年来稀土生物效应机理的研究进展。     

Single-molecule analysis of DNA uncoiling by a type II topoisomerase

Type II DNA topoisomerases are ubiquitous ATP-dependent enzymes capable of transporting a DNA through a transient double-strand break in a second DNA segment. This enables them to untangle DNA and relax the interwound supercoils (plectonemes) that arise in twisted DNA. In vivo, they are responsible for untangling replicated chromosomes and their absence at mitosis or meiosis ultimately causes cell death. Here we describe a micromanipulation experiment in which we follow in real time a single Drosophila melanogaster topoisomerase II acting on a linear DNA molecule which is mechanically stretched and supercoiled. By monitoring the DNA's extension in the presence of ATP, we directly observe the relaxation of two supercoils during a single catalytic turnover. By controlling the force pulling on the molecule, we determine the variation of the reaction rate with the applied stress. Finally, in the absence of ATP, we observe the damping of a DNA crossover by a single topoisomerase on at least two different timescales (configurations). These results show that single molecule experiments are a powerful new tool for the study of topoisomerases.     

基于SVM分类机的一种DNA序列判别方法

针对DNA序列类别的分属问题,提出采用支持向量机（Support Vector Machine,SVM）的方法进行分类。根据SVM分类器的要求建立特征属性空间,首先由每个DNA中4个碱基的含量得到4个特征属性,然后在此空间中扩充DNA序列长度的属性,最后根据SVM分类器对已知的DNA分类样本做训练得到分类超平面。利用此超平面检测所要分类的DNA序列,实验结果表明这种方法具有很好的分类精度。     

蚕豆在粉发育的细胞形态学研究

1、小孢子核从中央位移至一端后,花粉开始第一次有丝分裂。2、分裂末期出现成膜体、细胞板而形成分隔营养细胞和生殖细胞的细胞壁。生殖细胞壁含纤维素物质。3、生殖细胞壁在和花粉内壁连接处向内生长,直到二末端相遇而被掐掉,生殖细胞脱离花粉壁并进入营养细胞,而后壁消失。4 营养核和生殖细胞在花粉粒内互相贴近。然后,生殖细胞处于分裂前期并经变形变化和运动而发育成熟;营养核形状不规则。     

中间锦鸡儿花柱细微结构的研究

对中间锦鸡儿花柱的细微结构进行了观察，结果如下：１）表皮韭旬整齐，外切向壁加厚，具厚的角质层，细胞内赢在的淀粉颗粒；２）成熟花柱的通道细胞分泌面的细胞壁无传递细胞结构，但细胞壁厚且具角质层。分泌物开始溢出时角质层破裂和消失，细胞壁保留薄的一层，通道细胞内含一个中央大液泡，细胞质中有许多内质网、线粒体及少量质体；３）花柱的表皮与通道细胞之间为多层典型的薄壁细胞，细胞质内含少量线粒体、高尔基体及内质网     

微通道中细胞平动对其周围化学微环境的影响

主要通过数值模拟研究运动细胞在直通道中对周围浓度梯度场的影响,及对流传质Peclet数、细胞运动速度、细胞运动方向以及细胞大小对细胞周围浓度场的影响.研究发现,细胞在匀速运动一定距离后其周围的最大浓度差的大小和方向与相同位置静止情形下的值的偏差是一个常数,且此常数与传质Peclet数、细胞运动速度及方向、细胞直径等相关.该结论对细胞趋化效应的进一步量化研究具有重要意义.     

植物细胞膜的分布电荷所产生的细胞壁应力

根据细胞膜双电层模型和电学、力学原理，推出了植物细胞膜上电荷产生的细胞壁应力的计算公式；分析了植物细胞壁厚度、细胞半径以及细胞膜上电荷面密度变化对细胞壁应力产生的影响．获得了细胞膜上电荷对细胞壁三个方向的应力都有影响。细胞膜上电荷产生的细胞壁沿半径方向的应力增量比细胞壁另外两个方向的应力增量小得多；在细胞壁增厚过程中细胞膜上电荷产生的细胞壁各点的应力的绝对值变小；细胞膜上电荷所引起的细胞壁应力与细胞壁厚度以及膜上电荷面密度的关系是非线性的；在其他条件不变的情况下，细胞越大，细胞膜上电荷对细胞壁上的应力影响越大等几点结论．图5，参9．     

Fission yeast mod5p regulates polarized growth through anchoring of tea1p at cell tips

Microtubules have a central role in eukaryotic cell polarity, in part through interactions between microtubule end-binding proteins and the cell cortex. In the fission yeast Schizosaccharomyces pombe, microtubules and the polarity modulator tea1p maintain cylindrical cell shape and strictly antipodal cell growth. The tea1p protein is transported to cell tips by association with growing microtubule plus ends; once at cell tips, tea1p releases from microtubule ends and associates with the cell cortex, where it coordinates polarized growth. Here we describe a cortical protein, mod5p, that regulates the dynamic behaviour of tea1p. In mod5Delta cells, tea1p is efficiently transported on microtubules to cell tips but fails to anchor properly at the cortex and thus fails to accumulate to normal levels. mod5p contains a signal for carboxy-terminal prenylation and in wild-type cells is associated with the plasma membrane at cell tips. However, in tea1Delta cells, although mod5p remains localized to the plasma membrane, mod5p is no longer restricted to the cell tips. We propose that tea1p and mod5p act in a positive-feedback loop in the microtubule-mediated regulation of cell polarity.     

肉苁蓉(CistanchedeserticolaMa)胚胎学研究Ⅱ.胚和胚乳的发育

肉苁蓉为细胞型胚乳，初生胚乳核第一次分裂即形成细胞壁．具珠孔端胚乳吸器．种子成熟后由３～５层胚乳细胞包围着胚．合子横分裂形成顶细胞和基细胞．顶细胞纵分裂形成二分体和四分体，以后向各个方向分裂形成多细胞原胚．基细胞多次横分裂形成由一纵列细胞组成的胚柄．其胚胎发生属柳叶菜型．成熟种子中，胚仍然处于球形胚阶段．     

细胞悬液中细胞跨膜电位计算模型

由于建立外加电场中悬液细胞跨膜电位计算模型非常困难,本文用近似场等效方法解决了该建模难题．首先用Maxwell等效原理,计算处于外加场中细胞悬液的平均场．然后确定悬液中一个细胞局部的实际场分布和独立处于外加场中单细胞场分布近似等效的条件,再基于单细胞膜电位求解方法,建立反映均匀排列悬液细胞跨膜电位变化的计算模型．模型表明了细胞膜电位的变化和外加场、细胞种类、细胞浓度以及细胞排列方式的关系,揭示了悬液细胞相对单细胞跨膜电位下降的物理过程．最后用该模型计算了悬液中细胞跨膜电位并和数值解进行比较,结果基本符合．     

Cyclin D control of growth rate in plants

The mechanisms by which plants modulate their growth rate in response to environmental and developmental conditions are unknown, but are presumed to involve specialized regions called meristems where cell division is concentrated. The possible role of cell division in influencing meristem activity and overall plant growth rate is controversial, with a prevailing view that cell division is secondary to higher order meristem controls. Here we show that a reduction in the length of the cell-cycle G1 phase and faster cell cycling occur when the rate of cell division in transgenic tobacco plants is increased by the plant D-type cyclin CycD2 (ref. 8). The plants have normal cell and meristem sizes, but elevated overall growth rates, an increased rate of leaf initiation and accelerated development in all stages from seedling to maturity. We conclude that cell division is a principal determinant of meristem activity and overall growth rate, and propose that modulation of plant growth rate is achieved through regulation of G1.     

The emergence of geometric order in proliferating metazoan epithelia

The predominantly hexagonal cell pattern of simple epithelia was noted in the earliest microscopic analyses of animal tissues, a topology commonly thought to reflect cell sorting into optimally packed honeycomb arrays. Here we use a discrete Markov model validated by time-lapse microscopy and clonal analysis to demonstrate that the distribution of polygonal cell types in epithelia is not a result of cell packing, but rather a direct mathematical consequence of cell proliferation. On the basis of in vivo analysis of mitotic cell junction dynamics in Drosophila imaginal discs, we mathematically predict the convergence of epithelial topology to a fixed equilibrium distribution of cellular polygons. This distribution is empirically confirmed in tissue samples from vertebrate, arthropod and cnidarian organisms, suggesting that a similar proliferation-dependent cell pattern underlies pattern formation and morphogenesis throughout the metazoa.