The Origin of Life and Photosynthesis 



107 



tein molecule (see Fig. 17). It is likely that the membranes consist of 

 films of protein with a fatty layer between and it has been suggested 

 that the chlorophyll molecules form a film between the protein and 

 the fatty substance. 



It was shown by Hill in 1939 that the primary action which chloro- 

 plasts bring about in light is to split water into the two fragments or 

 radicals, H and OH, thus: 



H2O ^ H + OH 

 Oxygen is eventually liberated from the OH, while the reactive hy- 

 drogen atoms are available for doing chemical work. They will com- 

 bine with any suitable hydrogen acceptor. In the plant they are used 

 chiefly to combine with a coenzyme (dpnh)^ which is used to transfer 



♦-^st roma*4<*- granum 



repeating 250-270A 

 period J. * 



65X-i--i 

 30X|--_-. 



0-4 0-6y" 



FIG. 17. Part of section through a chloroplast showing the lamellae (Steinmann 

 and Sjostrand) 



the hydrogen to form energy-rich compounds. It has been suggested 

 that the function of the membranes in the protoplast is to keep H 

 and OH apart from each other so that they do not recombine. 



The overall reaction is to take carbon dioxide from the atmosphere 

 and 'reduce' it by the addition of hydrogen and the removal of oxy- 

 gen, so that it can be converted into carbohydrates. The course of 

 this reaction has been worked by Calvin and his associates by the use 

 of carbon dioxide labelled with radioactive carbon. They find that 

 the carbon dioxide enters into a complicated cycle of changes. It is 

 taken in at one stage of this cycle and the product is reduced to a 

 sugar-like compound by the dpnh, which has been formed from hy- 

 drogen atoms under the action of light in the protoplast. 



The main result of these researches was to show that the forma- 

 tion of sugars and other carbohydrates is not a simple direct process, 

 ^ Diphosphopyridine nucleotide, hydrogenated. 



