THE MECHANISM OF ORGANIC SYNTHESIS 111 



Carbon dioxide -f- Water 



I r 



(// not removed, destroys}^ CHLOROPHYLL 



f 



Hydrogen peroxide + Formaldehyde 



/ (// not removed, poisons) * 



/ 



ENZYME LIVING PROTOPLASM 



\ \ 



Oxygen Carbohydrates 



In thus reducing certain of the stages in the assimilation of carbon 

 to phenomena which can be imitated outside the living organism, we have 

 made considerable strides in the ' understanding ' of the process. The stage 

 for which the vitality of the chloroplast is absolutely essential is the formation 

 of starch from formaldehyde. Outside the body, our polymerisation of 

 formaldehyde results in the formation of a mixture of sugars which are optic- 

 ally inactive. The same process, in the living cell, leads to the production 

 of optically active sugars which are connected stereochemically and mutually 

 convertible one into the other, e.g. fructose and glucose. The derivatives of 

 protoplasm, containing asymmetric carbon atoms, are in the same way 

 optically active, and it seems that the asymmetry of the protoplasmic 

 molecule conditions a corresponding asymmetry in the substance which it 

 builds on to itself. The protoplasm furnishes, so to speak, a mould in which 

 polymerisation of formaldehyde can result only in the production of sugars 

 of certain definite stereochemical configurations. 



Few, if any, chemical reactions are pure. Nearly all are attended with 

 by-reactions, so that the yield of end product never attains 100 per cent, of 

 the theoretical yield. Even if the above mechanism be regarded as the 

 chief one, it is probable that side reactions take place at the same time, so that 

 we may have the formation of substances such as glyoxylic acid and other 

 derivatives of the fatty acid series. Such by-products might play an im- 

 portant part in the other synthetic activities of the cell, and especially in the 

 formation of fats and proteins. 



THE FORMATION OF PROTEINS 



Our knowledge of the mechanism by which proteins are synthetised in 

 plants is still more incomplete than that of the synthesis of carbohydrates, 

 and we are reduced in most cases to a discussion of the possible ways in 

 which, from our knowledge of the chemical behaviour of the constituents of 

 the protein molecule, we might conceive of its formation. We can at any 

 rate state the problems which have to be solved and study the conditions 

 under which the synthesis of protein is possible in plants and in animals. 



We know that plants are independent of any organic food for building 

 up their various constituents, whether carbohydrate, protein, or fat, pro- 

 vided only that they possess chlorophyll corpuscles and so are able to utilise 



