3 17Hn.CfiH.C0.0H = 



ITHg . CRH . CO . NH . CRK . CO . 1:H . CRH . CO . C H + 2 , KgO ; 



2 1^2. CRH. CO. OH -^ 



. CRH - CO .... 

 • CO- CRH --^ 



IvTH 



ITH + 2 HoO. 



(Emil Fisch3r, Unt arsuchungen iilDer Aminosauren, 

 Polyp 3ptide, und Prote^na, 1899 - 1906) 



Since proteins constitute the principi,!, 

 structure-building food for anirna^ls, and upon 

 digestion are chang ?d to amino acids in v/hich form 

 they are assimilated 03' the tissues, it is 

 generally thought that the phenomenon of grov/th 

 involv?s condensation xjroc^sses of a similar 

 character. 



Polypeptides will readily unite v^ith 

 additional amino acid molecules and thus undergo 

 a. process somewhat analogous to growth, "but the 

 different parts of the oolypeptide mol 3cul i? are 

 not fixadly coordinated with on 2 anothor in space 

 so that it lacks that d3finite morphology which 

 is characteristic of all living organisms. 

 Dik etopip erazin 3S, on the other hand, do possess 

 a somewhat more definit3 morphology, "but will 

 not condens 3 with additional amino acid molscules. 

 The essential characteristics of these two 

 structurss can, howev3r, be combined. 



If we assume that the valencies of the 

 carbon atom are arranged like the corners of a 

 regular tetrahedron, and that the three valencies 

 of tri-valent nitrogon in amino compounds are about 

 equally distributed- around an equatorial aircle, 

 (which arrangement appears to be the only one 

 vfhich is consistent with all known chemical facts,) 

 then the polypeptide chain, whan coiled around 

 on its-3lf, will assume the foinn of a spiral or 

 helix having substantially th 3 same diameter as 

 the diketopiperazine ring: 



