[Chap. XV SYNTHESIS OF STARCHES 135 



When 3 molecules of simple sugars unite by condensation, the result- 

 ant sugar is called a trisaccharide: 



Simple sugar > Water + Trisaccharide 



3 CeHioOe > 2 H2O + CisHssOie 



The formula Ci-Hi-Ou may also be written as (C<;HioO.-;)2H20. Like- 

 wise, the formula of the trisaccharide, CisHsl-Oi.;, may be written as 

 (C<>HioO.-,):^H20 to indicate the number of molecules of sugar utihzed in 

 the formation of the larger molecule. When 2 molecules of sugar unite, 1 

 molecule of water is released. When 3 molecules of sugar unite, 2 mole- 

 cules of water are released. 



A general name for the product formed by the union of several mole- 

 cules of simple sugars by condensation is polysaccharide. All these prod- 

 ucts are carbohydrates. We may now write a generalized equation that 

 represents the formation of any polysaccharide from a simple hexose 

 sugar, such as glucose or fructose. 



n CeHizOe > (n - 1)H20 + (C6Hio05)„H20 



One important point to note is that for every molecule of sugar added, 

 one molecule of water is liberated. This fact may be briefly represented 

 in a diagram in which we let some symbol, such as <I>, represent the 

 main body of the glucose molecule.^ 



Glucose + Glucose • Water + A disacchoride 



H0^(^^])^;H £Hbi-<(^^>-<)H . H,0 + HO-<^^^)^<K^3-OH, or (C.H,oO.),H.O 



Dissccharide + Glucose > Water + A trisaccharide 



HO-<^^><K^^]>0:H +;H0;<^^0H . H,0 i- H0<2^0x(^)mK;^0H, or (CH,oO.).H.O 



Disacchaiide + Disaccharide > Water + A polysaccharide of 4 {C,H,oO.) units 



^ The diagram in Chapter XVII indicating the arrangement of the atoms in a molecule 

 of sugar (glucose) shows the carbon atoms in a straight chain. The following arrange- 

 ment of the carbon and oxygen atoms is indicated by X-ray studies of polysaccharides. 



HO OH HO OH HO OH 

 \ / \ / \ X 

 HC CH HC CH HC CH 



/ \ / \ / \ 



HO— CH HC— OH HO— CH HC— O— CH HC— OH 



\ / \ / \ / 

 HC O HC O HC O 



CH2OH CH2OH CH2OH 



Glucose A disaccharide 



