4. 



The Ch3mic^l Basis of Life. 



If life cannot bo due, prirr.arily, either to 

 specific arrangaments of tissues or inemToranes or 

 to extrernely complex molecular structures, then 

 it must be due to some comparatively simple 

 principle of chemistry vrhich has not yet been 

 discovered. To find a cluo to this we must in- 

 vestigate the molecular structure of prot3ins, 

 because those constitute practically all the 

 structural material in the bodies of the simplest 

 unicellular organismiS after removal of the vat 3r, 

 Althougl': small amounts of fats ar ^ also present, 

 yet these do not constitute structural material 

 but appear to be merely the by-products of 

 certain kinds of protein metabolism. 



Protein substances, upon hydrolytic decom- 

 position, always yield a mixture of amino acids 

 or their dik etopip erazine derivatives. To the 

 alpha carbon atom of these acids thsra is alv/ays 

 attached one amino group and one hydrogen atom, 

 and usually also a more complex group, so that 

 they may be represented generally as foilov/s: 



ITH2-CKR-CO-OH. 



The structural formulae of the more im- 

 portant ar;:ino acids are as follows: 



