CHAPTER XIX 



DECOMPOSITION OF ORGANIC NITROGENOUS COMPOUNDS 

 RIPENING OF CHEESE AND OF MEAT 



ALL plant and animal tissues and cells contain proteins, 

 and frequently other complex nitrogenous compounds. They 

 probably are the most essential of the constituents of proto- 

 plasm. They contain the elements carbon, hydrogen, oxy- 

 gen, nitrogen, frequently sulphur or phosphorus, and some- 

 times iron. They may be characterized chemically as ex- 

 ceedingly complex nitrogenous compounds, which, when 

 hydrolyzed, break down into a large proportion of alpha- 

 amino acids. Conversely it may be stated that proteins are 

 built up by combinations of various amino acids. 



The general formula for the alpha-ammo acids is 

 RCH NH 2 COOH. Some nineteen or twenty distinct alpha- 

 amino acids have been found by chemists in their studies of 

 the hydrolysis of protein, that is to say, the R in the gen- 

 eralized formula may represent some nineteen or twenty 

 different groupings. The manner in which the proteins are 

 built up may be illustrated by the use of glycocoll, one of 

 the simplest of the amino acids, as an example. Glycocoll 

 is an amino-acetic acid, CH 2 NH 2 COOH. It has been found 

 possible by chemical means to cause two molecules of an 

 alpha-amino acid to unite with each other. It may be noted 

 that these acids contain both an acid (carboxyl or COOH) 

 and a basic (NH 2 ) group. The NH 2 (or basic portion) of 

 the molecule may be caused to combine with the carboxyl 

 radical of another. Disregarding the intervening steps 



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