Physical mutagens
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Radiation induced mutation
Ionizing radiation
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Ionizing radiations induce point mutations as well as various kinds of gross changes in chromosome structure such as deletions, duplications, inversions and translocations.
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The ionizing radiations such as X-rays (about 0.1 to 1 nm) are of high energy and can penetrate living tissues.
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In the process of penetrating matter, these high energy rays collide with atoms and cause release of electrons, leaving positively charged ions or radicals.
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These ions, in turn, collide with other molecules, causing the release of further electrons.
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The net result is that a “core” of ions is formed along the track of each high energy ray as it passes through matter or living tissues.
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This process of ionization is produced by X-rays, protons, neutrons, and alpha, beta and gamma rays released by radio active isotopes of the elements such as 32P, 35S or Cobalt-90 etc.
Non - ionizing radiation
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Ultra violet rays, having lower energy, penetrate only the surface layer of cells in higher animals and do not induce ionization.
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UV lights dissipate their energy to atoms that they encounter, raising the electrons in the outer orbital to higher energy levels, a state referred to as excitation.
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Molecules containing atoms in either ionic forms or excited states are chemically more reactive than those containing atoms in their normal stable states.
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The increased reactivity of atoms present in DNA molecules is the basis of mutagenic effects of UV and ionizing radiations.
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Ultra violet rays are readily absorbed by purines and pyrimidines in DNA, which then enter a more reactive or excited state.
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The maximum absorption of UV by DNA is at wavelength of 260 nm.
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Maximum mutagenicity also occurs at 260 nm, suggesting that the UV induced mutation process is mediated directly by the absorption of UV by purines and pyrimidines.
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Last modified: Saturday, 17 December 2011, 8:48 AM