Molecules Questions

However, in many in vitro and in vivo studies, the SCG assay has been shown to be a sensitive test for DNA damage. The experimental procedure of the SCG assay and the results published up to now are consistent with an interpretation in terms of detection of DNA strand breaks and alkali labile sites.The sensitivity of the test has been described as being similar to the DNA precipitation and alkali unwinding assays for detecting induced DNA strand breaks. Thus, at present, our study has to be taken as an indication that physical activity under certain circumstances may cause DNA effects.Future studies will have to show the mechanism underlying this effect.Such investigations will also contribute to a better understanding of the biological basis of the SCG assay.But the results presented here also have direct implications for the use of the SCG assay in studies with human blood cells.The results of in vitro and in vivo studies using human blood samples may be influenced by physical activities of the donor or days before the experiment.Mutat. Res. McKelveyMartin,V.J, G reen. M. H. L, Schmezer. P, PoolZobel,B.L, We obtain a ratio of for ssb:dsb for solid and cellular DNA and a preliminary ratio of about for base damage to strand breakage.Data are also given on specific characteristics of damage at the DNA level in the form of clustered damage of varying complexity, that challenge the repair processes and if not processed adequately could lead to the observed biological effects.It is shown that nearly of dsb are of complex form for lowLET radiation, solely by virtue of additional breaks, rising to about for highLET radiation.Inclusion of base damage increases the complex proportion to about and for low and highLET radiation, respectively.The data show a twofold increase in frequencies of complex dsb from lowLET radiation when base damage is taken into account.It is shown that most ssb induced by highLET radiation have associated base damages, and also a substantial proportion is induced by lowenergy electrons.In particular, track structure provides a basis for the understanding of the underlying mechanism that shape doseeffect relationships.There is a wealth of information and data accumulated on radiation biology that need to be placed in the framework of a general, descriptive theory.For example, there are considerable data on ionising ra diation tracks; on early effects of radiation on molecular targets such as DNA; on manifestations of DNA damage, after its processing by the cell machinery, in the form of chromosome aberrations, mutational events and genetic instability; on early clonal expansion of the cell to neo plasia; and on the final expression of malignancy.Over the past decade application of biophysical models to cellular DNA damage has advanced signifi cantly.This has come about through the availability of computer codes describing molecular interactions along the tracks of ionising particles, availability of fast computers and models of DNA in simple and more sophisticated forms. These descriptions have pro gressed from considerations of direct effects of radiation alone in the environment of the cell nu cleus, causing DNA damage in the form of singlestrand breaks, base damage and complex combinations within the cluster of damage.

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