86 Introductory Biology 



A. Glucides (Including Carbohydrates) 



The so-called glucides (glu' sid) (Gr. glykys, sweet) are a large group 

 of organic compounds which include the commonly known carbohydrates 

 (kar bo -hy' drate) (L. carho, carbon, coal; Gr. hydor, water) . The term 

 carbohydrates as used here implies "hydrates of carbon," in which the 

 ratio of hydrogen to oxygen is 2:1. The simplest carbohydrates in proto- 

 plasm are the simple sugars with the formula CeHioOe. Carbohydrates 

 are usually simpler in chemical structure than proteins but they never- 

 theless have a wide range of complexity among themselves. Like pro- 

 teins, the more complex carbohydrates may be split into simpler materials 

 by the action of enzymes. This happens when they are acted upon by 

 the enzymes of certain digestive juices. Through the proper chemical 

 action certain carbohydrates may be converted into fats, which explains 

 the proper selection of foods during prescribed cases of dieting. Carbo- 

 hydrates furnish elements which may assist in the building of protoplasm, 

 but their chief role is a readily available supply of heat and energy. 

 When glucose is oxidized (oxygen united with it), it yields water, carbon 

 dioxide, and energy; the latter, which originally held the sugar together, 

 now is available for use : 



GLUCOSE OXYGEN WATER CARBON DIOXIDE 



CeHaoOe + 6O2 "> 6H2O + 6GO2 + ENERGY 



Of the simple sugars, glucose (dextrose) is the only one present in 

 any quantity in the body for fuel purposes. Carbohydrates are stored 

 in animals as glycogen (animal starch) because the large molecules can- 

 not dialyze through the semipermeable cell membranes. Glycogen is 

 stored in the liver and muscles where it is converted as needed into 

 usable glucose, which has the following formula : 



H 



I 

 G=0 



1 

 H— C— O— H 



1 

 H— O— G— H 



1 

 H— G— O— H 



I 

 H— G— O— H 



I 

 H— G— O— H 



I 

 H 



Glucose (A Simple Sugar) 



