Properties and Activities of Living Protoplasm 87 



Glucides may be classified according to their complexity. The follow- 

 ing examples with their formulas will illustrate: 



1. Monosaccharides (mono -sak'' a rid) (Gr. monos, one; sakchar, 

 sugar), which contain one sugar group: glucose (dextrose or grape 

 sugar), CsHioOfi. 



2. Disaccharides (Gr. di, two), which contain two simple monosac- 

 charide sugar molecules: maltose (malt sugar), C12H22O11, and sucrose 

 (cane sugar or beet sugar), C12H22O11. 



3. Polysaccharides (Gr. poly, many), which contain several mono- 

 saccharides united: starch (CeHioOs)!! (in this case n is a rather large 

 number), cellulose, found in many plants (C6Hio05)x5 glycogen, or ani- 

 mal starch (CsHioOsIx (in these cases x is a larger number than the n 

 of starch) . 



B. Lipids (Including Fats) 



The group of organic compounds known as lipids (lip' id) (Gr. lipos, 

 fat) includes the true fats and a number of related fatlike substances 

 which have properties similar to fats but contain things in addition to 

 the fatty acids. Fats contain the same chemical elements as found in 

 carbohydrates but possess much less oxygen in proportion to the carbon 

 and hydrogen. Each molecule of a true fat is composed of one molecule 

 of glycerol (glycerine) and three molecules of some fatty acid, such as 

 stearic acid, palmitic acid, or oleic acid, etc. All fats contain glycerol 

 but differ in the kind of fatty acid combined with the glycerol. One 

 molecule of glycerol (C3H5[OH]3) plus three molecules of stearic acid 

 (CigHssOo) produces a common fat (in beef tallow) known as tristearin 

 (C57H110O6) . In the process, 3(H20) is given off. 



Fats contain twice as much heat energy as carbohydrates or proteins. 

 This accounts for their common use as foods in cold weather. One 

 gram of protein produces about 4 calories of heat and 1 gram of carbo- 

 hydrate, about 4 calories, while 1 gram of fat yields about 9 calories. 

 A calorie is a unit of heat measurement and is the equivalent of the 

 amount of heat required to raise the temperature of 1 gram of water 

 (1 c.c.) 1° C. 



Fats are used in the body in the construction of the plasma membrane 

 around the cells and the medullary (myelin) sheath around certain 

 nerve fibers. Fats are stored in various places as reserve supplies of 

 energy. Fats are stored under the skin to reduce body heat loss and to 

 round out the cavities between the tissues. Fats placed around such 



