256 ORIGIN OF STRUCTURES AND FUNCTIONS 



A chain constructed in this way would be subject to the 

 action of two opposing forces, the attractive force between 

 the non-polar, predominantly hydrocarbon, side chains, and 

 the repulsive force between the ionising amino acid radicals 



O 



O Q 



o 



Fig. 17. Diagram of the structure of the polypeptide 

 chain (after Talmud and Bresler). 



O — polar (ionising) groups 

 non-polar (non-ionising) groups. 



Fig. 18. Diagram of the coiling of the 

 polypeptide chain. 



(having similar charges at the given pH of the surrounding 

 aqueous medium). Owing to this, the chain would twist into 

 a spiral in the middle (nucleus) of which would be the hydro- 

 carbon (hydrophobic) groups while on the outside, which 

 faced the aqueous medium, would be the ionising groups 

 (Fig. 18). 



