CHAPTER III 



THE CHEMISTRY OF PHOTOSYNTHESIS 



Photosynthesis produces glucosides from carbon dioxide, 

 while respiration, in destroying them to extract chemical 

 energy, produces carbon dioxide> 



Respiration 



The work of Warburg and particularly of Wieland has 

 considerably increased our knowledge and understanding of 

 the process of respiration. 



From the chemical point of view, the passage from 

 glucose to carbon dioxide is made in two main stages, the 

 first from glucose to pyruvic acid and the second from pyruvic 

 acid to carbon dioxide. 



CgHigOe — ^CgH^Og — >-C02 



Pyruvic acid is the pivot of all these transformations. 

 The main biochemical routes of degradation of glucosides 

 regularly reach it, e.g., fermentations, but from there the 

 absence of oxygen diverts the reactions away from respiration 

 and carbon dioxide and in the direction of alcohol. 



The first stage begins by the fixation of a molecule of 

 phosphoric acid on the 6th atom of carbon of the glucose, 

 which thus becomes glucose-6-phosphate. This acid is fixed 

 by means of a diastase, hexokinase, and is provided by 

 adenosine triphosphate (commonly known by its initials ATP). 

 which becomes adenosine diphosphate, ADP. 



The glucose-6-phosphate isomerizes, i.e., transforms its 

 molecule, without any addition or loss, into fructose-6- 

 phosphate by means of another diastase, an isomerase. 



The hexokinase, which had fixed a molecule of phosphoric 

 acid on the 6th atom of carbon, intervenes again and another 



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