MONTE-CARLO SIMULATION OF DNA STRAND BREAKS INDUCED BY MONOENERGETIC ELECTRONS USING HIGHER-ORDER STRUCTURE MODELS OF DNA

A new theoretical model for estimating yield of initial DNA strand bre ak induced by several monoenergetic electrons is presented. It is base d on the Monte Carlo track structure simulation and on new DNA structu re models (one turn of double-strand DNA, nucleosome, solenoid), and l inks physical and chemical stages of radiation action. Direct and indi rect effects are strictly distinguished. Some results of calculations indicated: (1) the number of single strand breaks per nucleus (6 mu m in diameter) per Gy in pure water was about 10 times that in a cell en vironment (OH radical life time is assumed to be 8.7 ns). This is due to the difference in the time-dependent variation in the total number of the OH radical; and (2) the contribution of indirect effects to tot al damage decreased as the order of the DNA target model structure use d in the simulation increased (e.g. a one-turn model of double-strand DNA, similar to 98.4%; but the 30-nm solenoid model, similar to 86.1%) . This was due to the protective effect of histone protein against OH radical attack. Double-strand breaks were scored if two single-strand breaks were located on the same base pair. The present study indicated that the information from morphological and biochemical examinations of the cell environment must be considered more carefully with compute r simulation.