Study On The Effects Of Salt Concentration And Temperature On The Structure And Characteristics Of DNA

DNA (deoxyribonucleic acid) is the carrier of genetic information. Firstly, DNA transports genetic information into mRNA (message ribonucleotide) which is taken as a template of protein and translated into special protein sequences. By procession and modification of proteins, they come into being defined space configuration in order to perform all kinds of biological functions. The excellent elasticity of DNA and its complex make it as a kind of wonderful materials to make rigid molecule handle and manipulate other molecules. As DNA is regarded as a number of DNA-based units of nano-devise, more and more scientists pay attention to this research field. The particular structure and wonderful properties of DNA have tremendous application potential in biology, medicine, material science and so on. The structure and properties of DNA are related to environment (for example temperature, humidity, pH, salt concentration, et al.). The base-stacking and hydrogen-bond interactions change as environment condition varies. In order to further investigate the properties of DNA, we study the effects of salt and temperature on the structure and properties of DNA, and obtain some important results in this dissertation.1) Firstly, the structure characteristics and the effects of environment condition on the structure transition of DNA are described. Then the recent progresses of single molecule manipulation techniques that study the properties of DNA are introduced.2) We analyze the change of hydrogen-bond and the effects of salt concentration on hydrogen-bond and stacking interactions when DNA molecule is under external force. On the basis of ZZO model, we give a DNA model considering the hydrogen-bond and base-stacking interactions which are related to the salt ion concentration, and then discuss the force extension curves at various salt concentrations. With the salt concentration increasing, the stretching transition force increases nonlinearly. In addition, the folding angle distributions are obtained at different salt concentrations. When salt concentration is high, the distribution curve concentrates on the B-form configuration under given overstretching forces. With the decrease of salt concentration, the probability of S state increases rapidly, while the probability of B state decreases. When salt concentration decreases to some extent, the probability is very small for B state marking that this transition is easier to reach at low salt concentration than that at the high.3) The novel nonlinear dynamic model concerned with salt concentration is given and the melting transition of DNA is studied. The specific heat, entropy and melting temperature of system versus salt concentration are obtained. The nonlinear dynamic model of DNA is further studied on account of the effect of phosphate backbone. The effects of salt on denaturation transition are analyzed. By studying the nonlinear dynamic equation, we obtain the kink soliton solution of equation and discuss the influences of salt on phase transition force of DNA denaturation. The results show that melting phase transition is related to salt concentration and temperature. Solvent ion changes the structure and thermodynamic properties of DNA, and the melting temperature and phase transition force increase with the rise of the salt concentration. The width of kink soliton decreases and the energy needed for denaturation increases as salt concentration rises. 4) We measure Raman spectra of collagen and DNA at different temperatures. Raman spectra of DNA denote that all of the Raman peaks nearly have the same temperature dependence, two peaks are obtained at 38℃ and 82℃. These results are consistent with experimental data obtained by DSC (differential scanning calorimetry) at 82℃. The peak at 38℃ is concerned with the biological activity region of DNA function. No phase transition point is found at low temperature region. These spectra reveal that the vibrations of bases and phosphate groups are influenced by the change of the temperature. Base is the most sen...