Physics And Chemistry Basis Of Biotechnology - De Cuyper - tiera.ru

Philippe Lahorte and Wim Mondelaers
principles underlying accelerator technology are discussed in detail in paragraph 4.
Wardman (1991, 1994) has reviewed the value and applications of pulse radiolysis
measurements in free radical biology with respect to investigation of radical kinetic
properties.
From a theoretical point of view, the Monte Carlo method is generally considered
the most accurate method for calculating dose distributions. It is a statistical simulation
method which allows one to calculate the tracks of individual particles by sampling
appropriate quantities from the probability distributions governing the individual
physical processes using machine generated (pseudo-)random numbers. Average values
of macroscopic properties such as particle fluence, energy spectrum and absorbed dose
can then be obtained by simulating a large number of particle histories.
Microdosimetric Monte Carlo calculations allow for the modelling of the impact of
radiation on an atomic level. In this way direct and indirect damage to DNA might be
investigated by modelling the radiation formation of single and double strand breaks
(Briden 1999, Hill 1999; Moiseenko 1998a-b). However, also macroscopic properties
of chemical reactions such as rate constants, radiolysis end products and product yields
are amenable to Monte Carlo simulations (Bolch 1998, Hamm 1998).
The methods described above may be used in a wide variety of systems but none of
them yield substantial data that may be directly interpreted to give information on the
structure of the transient species. By contrast, the techniques available for studying
radicals in the chemical phase allow for the description of the chemical structure and
the characterisation of radical processes. As already mentioned, these will be discussed
in more detail in paragraph 3.
In the biological stage the consequences of irradiation are expressed in terms of
altered biochemical functions in the living species which can emerge after periods of
seconds (e.g. inactivation of enzymes) to years (e.g. development of cancers).
Evidently, techniques developed for research in this stage probe for the detection of the
radiation effects and the induced biochemical modifications. On the experimental side,
high performance liquid chromatography (HPLC) and gas chromatography (GC) can be
applied in combination with sensitive detection techniques such as electrochemistry
(EC) or mass spectrometry (MS) to monitor the formation of oxidative base damage
within cellular DNA (Cadet 1998, 1999). Alternatively, the single cell gel
electrophoresis (comet) assay can be used (Fairbairn 1995; Koppen 1999). The alkaline
type version of this assay can be applied to isolated cells and allows the measurement
of DNA strand breaks and alkali-labile lesions. The comet assay offers high sensitivity
at the cost of reduced specificity. The latter can be increased by using the assay in
combination with either DNA-glycosylases (in order to convert base lesions in
additional DNA strand breaks) (Pouget 1999a, b) or immunofluorescence detection
(Sauvaigo 1998). Because of the importance of strand breaks as critical lesions
produced by ionising radiation, a lot of effort has gone into developing methods
(currently routine methods in molecular biology and biotechnology) with which strand
breaks can be measured. Of these we mention the sucrose gradient sedimentation, the
non-denaturing filter elution and the nucleoid sedimentation technique (Prise 1998). Of
special importance has been the development of pulsed field gel electrophoresis (Iliakis
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