DNA双螺旋模型的建立过程

1953年,两位年轻的科学家——美国的沃森(J.D.Watson)和英国的克里克(F.H.C.Crick)发现了DNA双螺旋结构,这一发现是20世纪生物学的伟大成就之一,有人甚至认为,“在整个生物学史上比之双螺旋的发现,几乎没有更为决定性的突破。”(见迈尔:《生物学思想的发展》第843页)     

平行双螺旋DNA

平行双螺旋ＤＮＡ刘洋（吉林大学酶工程实验室,长春１３００６１）关键词平行双螺旋ＤＮＡ自１９５３年Ｗａｔｓｏｎ－Ｃｒｉｃｋ发现ＤＮＡ的反平行Ｂ型双螺旋结构以来,相继发现了单链螺旋、简单自组装螺旋、Ａ型双螺旋、Ｃ型双螺旋、Ｄ型双螺旋以及左手系的Ｚ型双螺旋...     

血液循环发现者哈维逝世三百周年纪念

1957年不但是生物分类学家林奈(CarolusLinnaeus,1707—1778)诞生250周年,同时也是生理学家哈维(William Harvey,1578—1657)逝世300周年。林哈二氏都是生物学史上杰出的人物,各自建立了不朽的功绩,为人类文化史     

DNA双螺旋的精细结构

70年代末,由于DNA寡聚体(短的DNA片段)单晶x射线衍射实验的结果,发现双螺旋参数随着序列的不同而起伏变化着——双螺旋的精细结构。本文综述了这方面的进展情况,重点介绍Calladine的解释;由DNA序列预测螺旋参数变化的Dickerson规则。其生物学意义在于:DNA碱基的序列信息可能贮存在双螺旋的局部精细结构之中。     

DNA双螺旋结构发现者——莫里斯·威尔金斯

莫里斯·威尔金斯是DNA双螺旋结构发现者之一,与沃森和克里克分享了1962年诺贝尔生理与医学奖。尽管如此,科学界对他的关注甚少,甚至一度遭受争议与批评。本研究较为客观地介绍这位伟大科学家在DNA双螺旋结构发现历程中的贡献。     

DNA双螺旋模型的建立——基因的物质本性

1953年,沃森和克里克阐明了他们关于DNA双螺旋结构的假说。沃森-克里克模型标志着分子生物学的诞生。沃森和克里克为遗传学乃至整个生命科学作出了非凡贡献。The Double Helix Model of DNA Structure——The Physical Nature of the GeneGAO Yi-zhiSoutheast University,School of Medicine,Nanjing 210009,ChinaAbstract:In 1953,Watson and Crick set forth their hypothesis for the double-helical nature of DNA.The Watson-Crick model had an immediate effect on the emerging discipline of molecular biology.It was a remarkable feat and highly significant in the history of genetics and biology.Key words：The Watson-Crick model;history of genetics     

华莱士:自然选择学说的共同发现者

简述了英国著名的博物学家、人类学家、探险家和生物学家华莱士的探险经历及其在进化生物学、生物物理学领域的贡献,让公众更为全面地认识被誉为生物地理学之父的华莱士在自然选择学说提出中取得的重要成就.     

从DNA双螺旋到人类基因组

从ＤＮＡ双螺旋到人类基因组朱立煌中国科学院遗传研究所１９５３年Ｗａｔｓｏｎ和Ｃｒｉｃｋ提出ＤＮＡ结构的双螺旋模型,阐明了遗传物质的复制机制,从而开创了用生物大分子的结构和功能来解释生命现象的新时期。ＤＮＡ双螺旋宛如一支光芒四射的火炬指引着人们去揭示生物的各种奥密。四十年来分子生物学,遗传学和生物化学的成就接踵而至,新发现层出不穷,新思想和新技术不断涌现,几乎囊括了诺贝尔生理学医学奖的大半而且常常名列诺贝尔化学奖的榜首。     

A Mathematical Model for Basepair Opening in a DNA Double Helix

In this paper, we consider a mathematical model that draws an analogy between a DNA molecule and a mechanical system consisting of two chains of interconnected pendulums. This model is designed to explore the dynamics of the system determined by rotational movements of nucleobases around a double-stranded pentose phosphate backbone. The workability of this model is assessed with respect to various factors: inhomogeneity of the chain of nucleobases, the properties of bonds in complementary pairs, and the formation of open states. It has been shown that simplified models for averaging the characteristics of the chain of nucleobases or simplification of the type of hydrogen bond in their complementary pairs influence the type of solution significantly, impairing the validity of the results. Therefore, the approach to the solution of rotational DNA molecule dynamics developed here is more consistent with its actual biomechanics. It is shown that the emergence of open states within nucleobase pairs and restoration of the closed structure may occur in the tested mathematical model.     

Structural Basis for Elastic Mechanical Properties of the DNA Double Helix

In this article, we investigate the principal structural features of the DNA double helix and their effects on its elastic mechanical properties. We develop, in the pursuit of this purpose, a helical continuum model consisting of a soft helical core and two stiff ribbons wrapping around it. The proposed model can reproduce the negative twist-stretch coupling of the helix successfully as well as its global stretching, bending, and torsional rigidities measured experimentally. Our parametric study of the model using the finite element method further reveals that the stiffness of phosphate backbones is a crucial factor for the counterintuitive overwinding behavior of the duplex and its extraordinarily high torsional rigidity, the major-minor grooves augment the twist-stretch coupling, and the change of the helicity might be responsible for the transition from a negative to a positive twist-stretching coupling when a tensile force is applied to the duplex.     

Temperature Dependence of the DNA Double Helix at the Nanoscale: Structure,Elasticity, and Fluctuations

Biological organisms exist over a broad temperature range of −15°C to +120°C, where many molecular processes involving DNA depend on the nanoscale properties of the double helix. Here, we present results of extensive molecular dynamics simulations of DNA oligomers at different temperatures. We show that internal basepair conformations are strongly temperature-dependent, particularly in the stretch and opening degrees of freedom whose harmonic fluctuations can be considered the initial steps of the DNA melting pathway. The basepair step elasticity contains a weaker, but detectable, entropic contribution in the roll, tilt, and rise degrees of freedom. To extend the validity of our results to the temperature interval beyond the standard melting transition relevant to extremophiles, we estimate the effects of superhelical stress on the stability of the basepair steps, as computed from the Benham model. We predict that although the average twist decreases with temperature in vitro, the stabilizing external torque in vivo results in an increase of ∼1°/bp (or a superhelical density of Δσ ?  + 0.03) in the interval 0–100°C. In the final step, we show that the experimentally observed apparent bending persistence length of torsionally unconstrained DNA can be calculated from a hybrid model that accounts for the softening of the double helix and the presence of transient denaturation bubbles. Although the latter dominate the behavior close to the melting transition, the inclusion of helix softening is important around standard physiological temperatures.     

Temperature Dependence of the DNA Double Helix at the Nanoscale: Structure,Elasticity, and Fluctuations

Biological organisms exist over a broad temperature range of −15°C to +120°C, where many molecular processes involving DNA depend on the nanoscale properties of the double helix. Here, we present results of extensive molecular dynamics simulations of DNA oligomers at different temperatures. We show that internal basepair conformations are strongly temperature-dependent, particularly in the stretch and opening degrees of freedom whose harmonic fluctuations can be considered the initial steps of the DNA melting pathway. The basepair step elasticity contains a weaker, but detectable, entropic contribution in the roll, tilt, and rise degrees of freedom. To extend the validity of our results to the temperature interval beyond the standard melting transition relevant to extremophiles, we estimate the effects of superhelical stress on the stability of the basepair steps, as computed from the Benham model. We predict that although the average twist decreases with temperature in vitro, the stabilizing external torque in vivo results in an increase of ∼1°/bp (or a superhelical density of Δσ?+0.03$\text{Δ}\sigma ?+0.03$) in the interval 0–100°C. In the final step, we show that the experimentally observed apparent bending persistence length of torsionally unconstrained DNA can be calculated from a hybrid model that accounts for the softening of the double helix and the presence of transient denaturation bubbles. Although the latter dominate the behavior close to the melting transition, the inclusion of helix softening is important around standard physiological temperatures.     

Osmotic Pressure of DNA Solutions and Effective Diameter of the Double Helix

Abstract

A simple osmometer with nuclear filters (polymer films with pores of a preset diameter) were used to measure the osmotic pressure of Col El plasmid DNA solutions in the concentration range of 1–4 mg/ml DNA. Linear and open circular DNA forms proved to have the same osmotic pressure within the experimental accuracy. The results of the measurements were used for calculating the second virial coefficient A ₂ of the solution of DNA segments and the effective chain diameter d _eff in the ionic strength range of 10^?2-0.1 M, As the ionic strength is lowered from 0.1 to 10^?2 M the effective diameter of DNA increases from 80 to 220 A. The results are in rather good agreement with theory and with other experimental data.