DNA凝聚过程中离子浓度效应及温度效应研究

More and more attentions have been put on DNA condensation, one of the most important reasons is related to the complexity of counterions. Recent experiments have pointed out that effects of temerature and concentration of counterions on the persistence length of DNA are more complex than the theoritical and experimental results before, the anions with different valence also have effects on the conformation and process of DNA condensation.Surprisingly,the DNA condensates more stably with the temperature increasing from 5℃to 53℃. Considering these important experimental phenomena, the following works will be carried out. First，based on the strong correlation model on DNA condensation propoed by us before, effects of temperature and concentration of counterions on DNA condensation and effects of temperature on the topology of DNA minicircle will be detected;second,with temerature changing gradiently, a magnetic tweezers experiment on DNA condensation will be carried out to detect the effects of temeperature during the process of DNA condensation. At the same time, a simulation work is also implemented by appling a constant force to the DNA molecule in the strong correlation model propoed by us before to imitate the single molecule experiment.The comparision between the theoretical and experimental results should show some highlights on the mechanism of DNA condensation.Finally,the DNA solution will be taken as binary mixing solution, and its thermodynamics will be investigated by considering the conformation entropy of DNA ,mixing entropy of the solution、and the translational entrpy between the DNA and solution enviroment around it to desclose mechanism of the dependence of DNA condensation on temperature.

DNA凝聚一直以来都备受关注，原因之一在于平衡离子的复杂性，最近实验又指出，温度、高价平衡离子浓度对DNA分子驻留长度的影响要比以往理论和实验结果复杂；不同价态阴离子浓度的增加会影响DNA分子凝聚构象和过程；随着温度升高，DNA凝聚更加稳定。鉴于此，开展以下探索工作:(1)基于我们已建立的DNA凝聚的强关联模型，研究温度、高价平衡离子浓度对自由DNA分子凝聚的影响；(2) 在温度梯度变化的情况下，开展研究DNA凝聚的单分子实验，研究温度变化对DNA凝聚过程的影响，并在已建立的DNA凝聚强关联模型中引入恒力，研究温度、高价平衡离子浓度对DNA凝聚过程的影响，并与单分子实验结果对比；(3)考量DNA溶液中DNA分子的构象熵，溶液的混合熵、DNA分子与周围离子环境间的平移熵等，研究该体系的热力学，揭示温度、溶液中阴离子浓度增加对DNA分子凝聚构象和过程影响的机制

通过执行国家自然科学青年基金“DNA凝聚过程中离子浓度效应及温度效应研究”，基本按照预定计划完成了研究内容。理论工作主要有四部分，（1）基于关联模型，主要考量离子浓度对DNA分子驻留长度影响，进而研究其对DNA凝聚过程影响，结果与目前实验结果吻合；（2）基于已有温度对DNA分子驻留长度影响结果及平均场理论，有效地规避系统地熵效应，DNA分子驻留长度对温度的依赖性对DNA分子凝聚过程有重要影响，结果与荧光单分子实验吻合；（3）在DNA以上模型中引入恒力作用，模拟DNA凝聚单分子实验，能够有效揭示DNA凝聚过程不连续等重要物理性质，与单分子实验结果吻合较好；（4）系统地研究温度对环状DNA分子拓扑结构的影响，对于环状DNA分子，连接数等于扭转数与环绕数之和，通过模拟直接得到环绕数分布，进而确定连接数分布。实验部分主要包含两类工作，（1）利用变温紫外分光光度计及等温滴定微量热仪系统地研究温度,离子效应对凝聚过程影响及凝聚过程中熵变等；（2）开展单分子实验，研究氟中毒机制及温度对DNA凝聚过程影响。

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