CHAPTER V 

 THE PROTEINS 



SECTION I. 



THE proteins form a group which is to be regarded as the most im- 

 portant of all organic compounds. They are obtained from all dead 

 cells, and are intimately connected with the life of the cell, for without 

 them as foodstuffs the cells cannot live. They are bodies of biological 

 origin; so far no effort to make them in the laboratory has been suc- 

 cessful. Most of the members of this group are amorphous bodies 

 of high molecular weight. The protein molecule is made up of the 

 elements carbon, hydrogen, nitrogen, oxygen, and sulphur. The 

 amounts of these elements vary considerably in different proteins, as 

 can be seen from the following table : 



The nitrogen and the sulphur are usually combined in two ways 

 loosely and firmly. The loosely combined portions of nitrogen can 

 be split off from the molecule, as ammonia, by heating with caustic 

 alkali. The loosely combined sulphur may be demonstrated by heating 

 with basic lead acetate and alkali when the black coloration due to 

 formation of lead sulphide occurs. All proteins when heated give 

 a smell of burnt feathers, due to the evolution of ammonia, pyridine, 

 and other bodies. 



The Constitution of Protein. 



The constitution of protein is exceedingly complex, 

 lated formulae for some proteins are as follows : 



The calcu- 



Egg albumin . . 

 Serum albumin . . 

 Haemoglobin (horse) 

 Haemoglobin (dog) 



C 



i39 



H 38 



Xl7 



L 720 

 H H71 



N 58 



78 



Ol40 

 0,!41 

 0214 



82 



I 



This complex constitution has been recently studied in two ways: 

 (1) by working out the products of the breaking down (the hydrolysis) 

 of different proteins; (2) by endeavouring to link together simple 

 cleavage products, and thereby produce some form of protein. 



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