Radiation Sensitivity and Biological Complexity
With the investigation of the action of radiation on bacteria, the initially declared aims of this book have been achieved: to discuss the most important molecular mechanisms causing damage, and to describe their action on elementary biological systems. A certain basic idea has been repeatedly confirmed during the discussion of radiation sensitivity; this is the concept of the target theory, which basically states that the radiation sensitivity of a biological system increases with the size of its sensitive target. The target in enzymes was shown to be the whole molecule (see Fig. 28), and in viruses and bacteria the total DNA (see Chapters 12 and 13). However, when the examples of single and double strand viruses are considered, the relationship between radiation sensitivity (1/D 37) and the DNA molecular weight, requires the use of different proportionality constants, which are referred to as inactivation probabilities (killing-efficiency, MW T /MW, Tables 15 and 16). The fact that different inactivation probabilities are obtained is due to the specific biological factors which decide whether or not a system can “survive” a specific lesion in the DNA, e. g. whether or not it can repair the lesion. It also, however, depends on the specific type of nucleic acid (single strand or double strand) and ultimately, if higher cells are included, on the specific arrangement of DNA in the chromosomes, which may even be present in multiples of the normal quantity (polyploidy).
KeywordsPrimary Ionization Diploid Cell Single Strand Break Radiation Sensitivity Biological Complexity
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