58 



UNITY AND DIVERSITY IN BIOCHEMISTRY 



1. Sucrose 



This is the sugar of the sugar-cane and sugar-beet. It is present in the 

 tissues and juices of many plants (carrot, beetroot, sweet fruits, sugar- 

 maple juice, sugar-cane, etc. . . .) 



In the molecule of sucrose, glucose is present in the a-glucopyranose form 

 and fructose in the /3-fructofuranose form. The two sugars are joined by their 

 two reducing groups and as a result sucrose has no reducing properties. 



(b) Reducing Diholosides 

 1. Lactose 



CH.OH 



CH,OH 



OH 



H OH 



jS-Galactopyranose 



H OH 



;8-Glucopyranose 



Lactose (/3 form) 



This is milk-sugar, it is present in the milk of all mammals (4% in cows 

 milk, 5-7% in human milk). 



Lactose is dextrorotatory, it exists in an a form and in a ^ form according 

 to the configuration of the remaining free pseudoaldehyde group. 



2. Maltose 



CH.OH CH,.OH 



o. 



HO 





H 



H 



HO 



OH 



H HO 



a-Glucopyranose 



H 



HO 



/3-Glucopyranose 



J 



Maltose (/3 form) 

 It is obtained when amylase acts on starch or glycogen ; it is dextrorotatory. 



3. Cellohiose " 



CHoOH 



H OH 



j3-Glucopyranose 



H OH 



|3- Glucopyranose 



Cellobiose (j8 form) 



