182 LIGHT, VEGETATION AND CHLOROPHYLL 



c 



N - C N 



HC 



\- 



C CH 



I N 



CH adenine 



/\ 

 OH OH OH H 9 ^9^^ 



I I I 111 

 HO-P-O-P-O-P-O-C-C- COH 



II II II III 

 O O O H H H 



ribose 



Y 



adenosine 



pyrophosphoric acid adenylic acid 



V 



Y 



Adenosine triphosphate (ATP) 



It enables the oxidations of the organism to be effected 

 by degrees. The total oxidation of a molecule of glucose is 

 capable of liberating 680,000 calories ; more than half of this 

 energy can be used for the formation of phosphoric bonds of 

 high energy. In this way reserves are built up to be used by 

 future reactions, but it is not impossible that this provision 

 is made at the expense of other sources of energy — luminous 

 energy, for example. 



Adenyhc acid intervenes in a slightly more complex form. 

 It unites through its phosphoric acid with phosphoric acid of 

 which the composition of the molecule is of exactly the same 

 type — with ribose and phosphoric acid — but in which the 

 organic base is not adenine but nicotinamide. This substance 

 is called diphosphopyridine nucleotide and is designated by the 

 letters DPN. 



