Evolution of Photosynthetic Mechanisms 



how pyridine nucleotide is created, but we know relatively little about 

 how ATP is created in oxidative phosphorylation in which the elec- 

 trons pass from reduced pyridine nucleotide through iron hack to 

 oxygen. This is one of the major problems of energy transformation 

 in all biological organisms. 



We have now split up the photo process of photosynthesis into 

 two other streams of evolutionary development, the stream which gave 

 rise to pyrophosphate (ATP) and the stream which gave rise to 

 pyridine nucleotide. Neither of these necessarily involves the photo 

 process directly. This leads us to the conclusion that the appearance 

 of the photo reaction, or the coupling of the photo reaction, with the 

 creation of ATP and of reduced pyridine nucleotide was a very late 

 thing in the evolutionary scheme. 4 You see that we are forced, now, 

 to consider the question of the origin of life in discussing the origin 

 of photosynthesis. We cannot dodge that issue, and we are indeed 

 considering it and doing so in a much more sophisticated way than 

 has been possible up until recent times. 



I shall indicate some of the states that we need, in order to try to 

 focus your attention on the separate evolution of mechanisms for 

 making ATP, mechanisms for making the molecules which are in- 

 volved in the creation of ATP today, mechanisms for creating pyri- 

 dine nucleotide, and, finally, how the light-capturing molecule, 

 chlorophyll, may have appeared and was coupled to the other energy- 

 transforming processes. This is really the story in principle, and I 

 now want to go through it quickly and try to give you some idea of 

 how I think these things might have occurred. 



Evolution of the Photosunthetic Apparatus 

 in the fire en Plant 



Figure 4 shows the apparatus in the green plant (the chloroplasts) 

 which is responsible for performing the process of photosynthesis. 

 It is perhaps necessary to say a few words here about the relationship 

 of the tangible physical material that performs photosynthesis as it 

 can be seen on the subcellular, but still visible, level. I shall then dis- 

 cuss the macromolecular level (where this apparatus cannot yet be 

 seen), and, finally, go to the substrate level where we can again deal 

 with things in a chemical way. 



Three different kinds of chloroplasts are shown in Fig. 4, illustrating 

 the highly ordered array of layers in all of the three types of organ- 

 isms: a unicellular green alga, a blue-green alga which does not have 



