16:2/ Molecular Action of Ionizing Radiations 301 



of water being eliminated for each nucleotide joined to the chain. 

 Both proteins and nucleic acids are complicated high polymers in that 

 the long chains consist of a mixture of different types of residues or 

 monomers arranged in a definite but complex pattern. It is easier to 

 interpret the effects of ionizing radiations on simpler synthetic polymers, 

 made up of one or at most two types of monomers, than on the more 

 complex proteins and nucleic acids. A study of the radiation damage 

 to these simpler polymers provides orientation toward the types of effects 

 to be expected when proteins and nucleic acids are exposed to ionizing 

 radiations. 



Studies have been made of the effects of ionizing radiations on many 

 different types of synthetic high polymers. Two used as examples in the 

 next section are polyethylene and polyisobutylene. They have the 

 structural forms shown in Figure 1 . 



HHHHHHHH 



— C— C— C— C— C— C— C— C 



H H H H H H | H 



HCH 



HCH 



I 

 HCH 



HCH 



I 

 H 



Polyethylene has branched sidechains. 



It is an "addition" polymer of 



ethylene, CH2=CH 2 . 



CH 3 CH 3 CH 3 CH 3 



— C— CH 2 — C— CH 2 — C— CH 2 — C— CH 2 — 



CH 3 CH 3 CH 3 CH 3 



Polyisobutylene is an "addition" 

 polymer formed from isobutylene. 



CH 3 



\ 



C=CH 2 



/ 

 CH 3 



Figure I. Structure of polyethylene and polyisobutylene. 



When the monomers (ethylene) molecules are added together to form 

 polyethylene, it is possible to have carbon atoms surrounded by only 



