Raman Spectroscopic Studies On The Damage To DNA Caused By Ultraviolet Irradiation

In this thesis, we mainly investigated the influence on biological macromolecules-DNA by different intervals of ultraviolet irradiation (UVA-ultraviolet A: 320 ~ 400nm, UVB-ultraviolet B: 280 ~ 320nm and UVC-ultraviolet C: 100~280nm)using Raman spectroscopy. At the same time, we compared the difference of damage by them to DNA. The results of this research are helpful in understanding the interactions between ultraviolet and DNA in molecular level, and will provide theoretical guidance and reference for the protection and treatment of some diseases caused by ultraviolet irradiation. After repeated experiments, we got some results as the following.UVA can just do slight damage to the B form backbone of DNA, but it can reduce the B-form DNA components to some extent, cut off some phosphodiester bonds and damaged the main chain spatial structure of DNA in some sense. In the contrast, UVA damaged the deoxyribose and base pairs more seriously: some moieties were destroyed and some base pairs were modified. On the other hand, UVB can do some damage to the main chain structure of DNA, and the damage to the structure of nucleotides was serious. Some glycoside bonds might be cut off and some purine and pyrimidine must be excided. Just as UVA, UVB can also reduce the B-form DNA components.UVB was different form UVA in that the former damaged the deoxyribose moiety faster. UVB damaged all bases in some extent, among which the damage to pyrimidine was more significant than that to purine bases. So, in some sense, there might have formed some cyclobutane pyrimidine dimmers (CPDs) and (6-4) photoproducts.UVC can damage DNA more severely than UVA and UVB. After certain period of time of UVC irradiation, the damage to the B-form main chain structure of DNA was significant, some phosphodiester bonds were cut off and the B-formDNA structure was modified. However, UVC cannot reduce the B-form DNA content as UVA and UVB do. UVC damaged DNA in a complete way: glycoside bonds and phosphodiester bonds were cut off, some single or double chains of DNA were ruined and the B-form structure of DNA was modified. The damage to the base pairs moieties by UVC was fatal. Not only happened the excision and modification of some bases but also many link bands were cut off.Among all the moieties of DNA, the pirimidine bases and deoxyribose may be the first to be damaged by UV. What's more, different intervals of UV have their own characters in influencing DNA: the damage to some bases by UVA may be more serious than that by UVB, and UVB did more severe damage to some deoxyribose than UVA; however, as far as the pyrimidine bases are concerned, the damage by UVB is by far more serious than that by UVA. These results may indicate that there are preferential damaging sites on DNA molecules caused by UVA and UVB irradiation. Moreover, with UVA or UVB irradiation for a long time, the photoreactivation of DNA occurred. The serious damage to deoxyribose and bases by UVB and UVC may confirm the conformation of cyclobutane pyrimidine dimers (CPDs) and (6-4) photoproducts.Besides, we introduced Raman theory and corresponding experimental apparatus in detail, and gave out a prospect of the development and applications of Raman spectroscopy.