CHAPTER V 



CARBOHYDRATES AXD THEIR HYDROLYZING ENZYMES 



THE carbohydrates which occur in plants may be classified as 

 follows : 



f Pentoses, C 5 H 10 O 5 Arabinose, xylose. 

 Monosaccharides ...... JHexoses, C.H M O Glucose, galactose, 



mannose, laevulose. 



Disaccharides ......... {Sucrose, maltose, 



T i isaccharides ......... {Raffinose and others. 



f Pentosans, (C 5 H 8 O 4 ) n Araban, xylan. 

 Starches, (C 6 H 10 O 5 ) n Starch, dextrin, inulin. 

 Polysaccharides ...... ^ Mannans, galactans, gums, mucilages, 



pectic substances. 

 Celluloses, (C 6 H 10 O 5 ) n . 



The carbohydrates are widely distributed in plants and form most 

 important parts of their structure. Those most commonly found are : 

 cellulose, starch, pentosans, dextrin, glucose, sucrose, laevulose, and 

 maltose. Other sugars, especially trisaccharides, are known in addition 

 to those mentioned above, but they are somewhat restricted and specific 

 in their distribution. 



As in the case of the proteins, so with the carbohydrates, the molecules 

 of the more simple and soluble crystalline compounds, such as the 

 monosaccharides, are synthesized into more complex molecules which 

 exist, either in the colloidal (dextrin), or insoluble state (starch, cellulose). 

 The last-mentioned build up parts of the solid structure of the plant. 

 The resolution of the solid complex substances into simple ones is 

 known in many instances to be brought about in the plant by enzymes, 

 and it is highly probable that the synthesis of the complex from the 

 simple is also controlled by these enzymes. 



The most commonly occurring sugars in plants are glucose, laevulose, 

 sucrose and maltose : sucrose is hydro! yzed by the enzyme, invertase, 

 into one molecule of glucose and one molecule of laevulose : maltose by 

 the enzyme, maltase, into two molecules of glucose. Both invertase and 

 maltase are widely distributed. The connexion between various sugars 

 and photosynthesis, and their inter-relationships with each other in the 

 leaves, are reserved for another section. 



