BIOLOGICAL 

 CHEMISTRY 



Section I 



CHEMICAL AND PHYSICAL 



CHAPTER I 

 ORGANIC CHEMISTRY 



THE energy required for living organisms is obtained 

 from compounds containing carbon. The branch of 

 science that deals with compounds containing carbon 

 ; called organic chemistry. 



The heat energy that can be obtained from an organic 

 .substance is measured by burning it in the presence of oxygen : 

 the heat so produced is absorbed and measured in calories. 

 This heat of combustion is not the same as the available or 

 usable energy, but until the available energy has been 

 measured we must confine our attention to the heat value 

 obtained on combustion. 



A calorie (c) is the amount of heat required to raise one 

 gramme of water from 15 to 16 C. For many purposes this 

 unit is too small, so a large calorie (C) is used which is equal 

 to 1,000 calories. 



In dealing with biochemical oxidations, we must remember 

 that the reaction takes place in solution, therefore we must 

 add the heat of solution of the products of reaction to and 

 subtract the heat of solution of the original substance from 

 the heat of combustion obtained in the ordinary way. Further, 

 any subsidiary reaction that results may furnish energy to 

 the reacting system. 



Four elements are sufficient for the construction of the 

 groups of substances dealt with in this chapter. Each of 

 these elements possesses certain valencies or combining 

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