190 



APPENDIX 



water to form hydrogen peroxide, which is immediately 'decomposed by 

 the catalase of the cell with the liberation of 2 . The formaldehyde 

 would destroy the cell if it were not immediately polymerized by the 

 action of the green bodies, chloroplasts. 



The most important sugars are the hexoses or those with six carbon 

 atoms, which are asymmetrical. The carbon atom has four valences and 

 if a different kind of atom or group is attached to each of these valences, 

 the molecule is asymmetrical, that is to say, no point, line or plane of 

 symmetry exists. It is then possible to arrange the groups around the 

 carbon atom in two different ways so that one form of molecule will be 

 the mirrored image of the other. Such asymmetry can be detected be- 

 cause a molecule containing one asymmetric carbon atom rotates the plane 

 of polarized light to the right or the left. If a molecule contains two 

 asymmetric carbon atoms, both atoms may rotate in the same direction 

 or in opposite directions, and if the rotation is equal in opposite directions 

 the molecule appears inactive to polarized light. There arc often obtained 

 mixtures of equal numbers of dextro-rotatory and laevo-rotatory mole- 

 cules, the mixture does not affect polarized light and is called racemic. 



The hexoses that are readily assimilable by mammalian cells are : 



CHO 

 1 

 HCOH 



I 

 HOCH 

 I 

 HCOH 



I 

 HCOH 



I 



CH 2 OH 

 d-glucose 

 (dextrose 



CHO 



I 

 HOCH 



I 

 HOCH 



I 

 HCOH 



I 

 HCOH 



I 



CH 2 OH 

 d-mannose 



CHO 



I 

 HCOH 



I 

 HOCH 



I 

 HOCH 



I 

 HCOH 



I 



CH 3 0H 

 d-galactose 



CH s OH 



I 

 CO 



I 

 HOCH 



I 

 HCOH 



I 

 HCOH 



I 



CH.OH 

 d-fructose 

 (laevulose) 



This is the nomenclature of Fischer, based on structural formulae. AH 

 of these sugars are aldehydes (aldoses) and rotate polarized light to the 

 right, except d-fructose (a ketose) which is usually 'called laevulose be- 

 cause it rotates polarized light to the left. 



On the oxidation of 1 g. glucose about 3.74 calories of heat are pro- 

 duced. 



Glucose, fructose and galactose, when reduced, are converted into the 

 alcohols, sorbite, mannite and dulcite. Glucose on mild oxidation, yields 

 gluconic acid, with the COOH group formed from the CHO group. On 

 further oxidation another COOH group is formed on the other end of 

 the chain, and thus the dibasic acid, saccharic acid is formed. Glucose, 

 as well as other hexoses, is easily transformed into lactic acid without 

 oxidation. One molecule of glucose yields two molecules of lactic acid, 

 CH 3 CHOHCOOH, when acted on by lime in sunlight or by bacteria, or 

 other living cells. 



As aldehydes or ketones, the hexoses are reducing substances, but this 

 property may be lessened spontaneously, in solution, by what is called 

 lactone formation. In this, the double bond between one carbon and 

 oxygen atom, to which the reducing character is due, opens out and one 

 bond becomes applied to a distant carbon atom in exchange for an OH 

 group. 



Glucose may combine with other substances, forming glucosides. This 

 combination is usually preceded by lactone formation. Two hexose mole- 

 cules may combine by the opening out of a double bond and the elimina- 

 tion of one molecule of water, forming a disaccharide molecule. Thus 



