Study Of Lesion And Repair Of DNA After Irradiating By Heavy Ions

DNA is considered to be the most important bio-macromolecule and main target molecule responsible for all biological effects. Many kinds of damage can be induced by direct radiation or indirect effect of free radical. DNA double strand breaks (DSBs) are considered to be the most important initial damage responsible for all biological effects induced by ionizing radiation. Whether DNA lesion is repaired accurately or not, which is relation to mutation of gene, fate of cell and canceration. Through studying DNA DSBs induced by heavy ions, it is important significant for cancer therapy by heavy ions , medicament against radiation and the dangerous assessment of radiation.In the subject, DNA DSBs produced by ~7Li ions irradiation are studied in experiment and theory. The most work is as follows:In experiment, DNA samples are irradiated by the ions beam after scattering equably by Q3D in place of irradiating directly through the scanning pipeline.(1) Effects of LET and free radical in the DNA double strand breaks produced by 7Li ions irradiation are investigated using the Atomic Force Microscopy (AFM). The experiment is performed at the HI-13 Tandem Accelerator Nuclear Physics National Laboratory of China Institute of Atomic Energy (CIAE). The DNA samples in TE-buffer are irradiated with dose of 1 0Gy. The number of shorter fragments of linear form DNA irradiated by high-LET ions is largerthan by low-LET ions. It shows that high-LET radiation induces DSBs more . When the mannitol is mixed with DNA, the intact circular form DNA is still observed using AFM. It indicates that the free radical has definite effect in the DNA double strand breaks induced by heavy ions.(2) The experiment of DNA end-joining catalyzed by cell-free extract is performed after 7Li ions radiation. The result of gel electrophoresis shows that there are not dimmer and the fraction of linear fragment increases in proportion to the supercoiled form DNA. We try to explain the reason of the phenomenon.In theory, the length distribution of DNA fragments induced by 7Li ionizing radiation is fitted with the random breakage model. The fitting result shows that the random breakage model cannot describe the distribution of DNA fragments in lower doses, while the random breakage model can reproduce the experimental data in higher doses. It indicates that the length distribution of DNA fragments has random statistical feature in higher doses. The Tsallis model is attempted to fit the length distribution of DNA fragments. The fitting result shows that the same problem is in existence.