Evolution of Photosynthetic Mechanisms 



a chloroplast (the layers are still present, however, winding their way 

 in and out through the entire cell), and a chloroplast from a higher 

 plant (tohaccol showing the layering of the green material very 

 clearly. The layers (lamellae) themselves are constructed of arrays 

 of macromolecular suhunits which we now think we can see.- 8 Figure 

 5 gives a model for chloroplast lamellar structure and Fig. 6 is an 

 electron micrograph of frozen dried spinach chloroplast supernatant. 



f 



160 A 



I 



INTERGRANA AREA > 



GRANA AREA 



FIG. 5. Model for the lamellar structure within a spinach chloroplast: (a) 

 Osmium-staining layer of the lamellar structure. Thickness 30 A in the intcrgrana 

 regions and 60 A in the grana regions. <6) Particles forming the granular inner 

 surface of the two layers making up the lamellar structure. The packing of ohlate 

 spheres would not he as simple as illustrated, since the central axis of hoth layers 

 would not be in the same vertical plane shown here. 



Figure 4 shows the high degree of order in the chloroplasts, and, 

 furthermore, that this high degree of order exists in other elements 

 in the cell, such as the mitochondria, which perform other functions 

 ( formation of ATP by oxidative phosphorylation of pyridine nucleo- 

 tide ) , 29 The purpose of Fig. 4 is to show the similarity of structure 

 hetween the photosynthetic apparatus and material which is not 

 photosynthetic, and to show also that it is a highly ordered array in 

 all cases. This highly ordered array must be achieved in some s) s- 

 tematic way from molecules which themselves are ordered by virtue of 

 the atoms of which they are made. 



