84 A. I. EINGER 



in water, and are nut coagulated by heat. They turn red litmus blue. Bc- 

 causo of their basicity they have the power of absorbing carbon dioxid 

 from the air, forming carbonates. They form stable salts with mineral 

 acids and have the power of precipitating other proteins. 



The conjugated proteins will be taken up in a separate chapter. The 

 derived proteins will b< discussed in the chapter on digestion. 



The Structure of the Protein Molecule 



It has been known for a long time that if acids, alkalis or digestive 

 ferments like pepsin or trypsin be allowed to act on protein under suitable 

 conditions, there sets in a decomposition of the protein molecule, which, 

 if carried on for a long enough time, will cause an almost complete disap- 

 pearance of the protein. In the process of this decomposition a number 

 of cleavage products are produced which have been isolated, purified and 

 identified. They are all amino acids i. e., organic acids which have an 

 oniino ( NH 2 ) radical attached to their o-carbons. These amino acids 

 are obtained from the splitting of all proteins, and because of that they are 

 known as the "building stones" of protein. To date, twenty-one different 

 amino acids have been obtained as cleavage products cf the protein mole- 

 cule, and there is every reason to believe that the list is not yet complete, 

 though it may be said with certainty that the most important ones have 

 been accounted for. 



Amino Acids or "Building Stones of Protein" 



The known amino acids may bo considered under the following head- 

 ings : 



A. Monobasic Mono Amino Acids, 



1. Glycocoll or glycin or a-amino acetic acid. 



CH 2 1S T IL, 



I 

 COOII 



2. Alanin or a-amino propionic acid. 



CH 3 



a-CHNH 2 

 COOII 



