BIOLOGICAL CHEMISTRY 



CH 2 OH CH 2 OH CH 2 OH 



Aldehyde Sugar. Glycerine. Ketone sugar. 



Glycerine, like other alcohols, can unite with acids, giving 

 rise to organic salts or esters, to which we must return under 

 the heading of " Fats." 



The most frequently occurring carbohydrates, unlike 

 glycerine, do not contain three carbon atoms (triose), but six 

 (hexose), or some multiple of six carbon atoms. The six 

 carbon atom sugars are called monosaccharides, and mul- 

 tiples of six are called di-, tri- and poly-saccharides. 



When the hexoses unite to form disaccharides water is 

 removed and the process is known as dehydration or condensa- 

 tion. The reverse process of breaking down the polysaccharides 

 into hexoses is accompanied by the addition of water and is 

 known as hydrolysis. 



Some sugars are known which contain less than six carbon 

 atoms, and those with five carbon atoms (pentoses) are found 

 in most cells. 



The reactions of the various sugars can be foretold from a 

 knowledge of the groups contained in them and the relative 

 position of the groups to each other. 



We shall now examine the chief reactions for carbohydrates. 



Trommer's Test.* This well-known reaction can be de- 

 scribed as taking place in two stages. On adding copper 

 sulphate to a solution of sugar and then rendering alkaline 

 by sodium or potassium hydroxide, a blue precipitate occurs, 

 which dissolves in excess of alkali, to form a clear blue solution . 

 The sugar owes its power of holding copper hydrate in solution 

 to the hydroxyls of the alcohol groups. Many other substances 

 besides sugar form a blue solution with copper hydrate, 

 e.g. glycerine, tartrates, citrates, ammonia, etc. 



On heating the clear blue solution the cupric hydroxide is 

 reduced to cuprous hydroxide, and the latter loses water to 

 form cuprous oxide : hence a yellow precipitate is formed 

 which soon turns red. The sugar is oxidised. This portion 

 of the test is due to the presence of the free aldehyde or 

 ketone group. Although ketones do not reduce copper salts 

 the presence of alcohol hydroxyl groups on the neighbouring 



* Trommer, Ann. d. Chem. u, Phar-m., 1841,. vol. 39, p. 360. 



