Single-molecule Analysis Of The Interaction Between DNA And Chitosan

DNA condensation is the process of condensing free DNA molecularinto some compacted and consistent structures, which is an important partof gene therapy. The development of the single molecule approaches,such as magnetic tweezers and atomic force microscopy, makes itpossible further study of the condensing process of DNA caused bychitosan. The research is roughly divided into two parts:Firstly, we use AFM technology to study the morphologicalchanging pattern of the complex produced by the interaction betweenPbr322DNA and chitosan. The results show: with the charge ratio(k)increase from2to around4, the sphere-to-rod ratio of the complexdecrease from2to around0.75. At the same time the size of the complexalso decrease from0.3um to0.1um.Secondly, we use AFM and MT technology to study the condensingprocess of λ-DNA induced by chitosan. The results show that with theincrease of the charge ratio(k) from0.2to5, free DNAs come intocompacted structures and they have obvious boundary. At the same time,when the k increase from0.5to4the sphere-to-rod ratio decreased from5to1, the size of the complex decreased from0.2to0.1um. As we knowthat the PH influence the effect of the complex in gene therapy, when PH>7.4the stabilization of the complex decrease obviously. The experimentproves this conclusion: when keep the k equal to4and change the PHfrom7.4to8.5. Through comparing the results of the AFM, we can confirm that with the increase of PH the number of free DNA increases.By comparing the images of PBR322-DNA andλ-DNA at the same k,we found the former one with better decentralization and smaller size andthe forming rule of the complex are the same. The MT experiment resultsindicate that with the increase of k from3to4, the reaction time decrease,and the jumps in the curve increase. By doing the experiment severaltimes with the same k value, we found that the condensing forceincreased with k: when the k increase from2to7the cohesion forceincrease from0.5pN to4pN. At the same time we statistic the step size ofthe DNA induced by chitosan and we find the step size are almostcentralize in200-500nm.