196 



Cellular Events Produced by Ionizing Radiations /I0 : 5 



amino acid cysteine, which tend to react with free radicals formed in the 

 irradiation of water, limit the cellular damage of ionizing radiations. 

 Both the oxygen effect and that of the protective agents can be inter- 



Prophase. Ultraviolet irradiation of 

 the cytoplasm causes spindle to disappear. 

 Much greater doses are needed 

 than those necessary in direct 

 irradiation of the chromosomes. 



Irradiated 

 area 



(b) False metaphase. 



Chromosomes fail to line up 

 at equatorial plate. 



(c) False anaphase. Cell constriction starts, 

 but chromosomes fail to divide . 



(d) In telophase, two new nuclei form. 

 The chromosome division is uneven 

 and the cells eventually die . 



Figure 7. Diagrammatic representation of abnormal cellular 

 division resulting from cytoplasmic irradiation with ultra- 

 violet photons. All spots in the cytoplasm are equally 

 sensitive. 



preted to support the role of free radicals such as 2 H and OH as the 

 primary elements in the cellular action of ionizing radiation. However, 

 they can be equally well interpreted as altering the products formed by 

 the direct interaction of the ionizing radiation with the chemical con- 

 stituents of the cells (see Chapter 16). 



5. Genetic Effects 



At dosage levels producing little or no visible cellular damage, it is still 

 possible to alter the genetic material of the cell so that the progeny will 

 be different. This is true whether one uses simple one-celled plants 

 and animals, or complex organisms such as the mammals and the higher 

 plants. In every case, these genetic effects occur within a single cell 

 and may be classed as cellular events. Just like the visible changes 



