6 4 



THE CARBOHYDRATES 



towards hydrolytic agents, such as mineral acids or enzymes. 

 Thus there are a considerable number of naturally occurring 

 sugars containing five and six carbon atoms which cannot be 

 hydrolysed ; such sugars form a group known as monosacchar- 

 ides* On the other hand many sugars are known which on 

 hydrolysis break up into two molecules of monosaccharide 

 according to the equation 



C U H M U + H 2 = 2C 6 H ia O fl 



Such sugars are known as disaccharides. 



Similarly sugars which on hydrolysis give three molecules 

 of monosaccharide as follows 



C 18 H 32 16 + 2 H 2 = 3C 6 H 12 8 



are termed trisaccharides. 



Finally, carbohydrates, such as starch and cellulose, which 

 on hydrolysis yield an unknown number of molecules of mono- 

 saccharides are classed as polysaccharides. 



The nomenclature of the monosaccharides is based on 

 the number of carbon atoms in their molecules, those contain- 

 ing five being called pentoses, while those containing six atoms 

 are known as hexoses. For this reason the use of the terms 

 monose and biose in place of monosaccharide and disaccharide 

 is to be deprecated owing to the confusion which is liable to 

 result therefrom. 



Sugars. - 



Monosaccharides. 



Disaccharides. 



( Pentoses (C 5 H 12 O 5 ). Arabinose, Xylose, 



Rhamnose, Fucose, 

 Quinovose. 



Hexoses (C 6 H 12 O 6 ). Dextrose, Levulose, 

 Sorbose, Galactose, 

 Mannose. 



(C 18 H^ 8 O U ). Sucrose, Turanose, Maltose, 

 Isomaltose, Cellobiose, 

 Gentiobiose, Trehalose, 

 Lactose, Melibiose. 

 (C U H 20 O 10 ). Glucoxylose, Primeverose, 



Vicianose. 



Trisaccharides (C^H^O^). Raffinose, Melecitose, Gentianose. 

 Tetrasaccharides (C ?4 H 42 O 21 ). Stachyose. 

 t Unknown Constitution. Lupeose, Agavose. 



* The artificially prepared tetroses, heptoses, octoses, and nonoses also belong 

 to this group, but as they do not occur in nature, as far as is known, they need 

 not be considered here. 



