l8f 



"^J^ Pigments 



Of major importance among the biosynthetic pathways 

 of the chloroplast must be those leading to photosynthetic 

 pigments. Akhough some of these may vary from one organ- 

 ism to another, all organisms must be capable of making at 

 least one of the chlorophylls, carotenoids, and hematin pig- 

 ments. During photosynthesis the simple precursor molecules 

 for these synthetic paths are available from the carbon reduc- 

 tion cycle, whereas the reduced pyridine nucleotides and 

 ATP are of course at high levels in the chloroplast. 



Carotenoids and phytol 



The starting point for the synthesis of carotenoids and 

 phytol, as well as steroids and terpenes, is acetyl CoA. In the 

 previous sections we discussed routes from the carbon reduc- 

 tion cycle to acetyl CoA. These are shown in Figures 7 and 9. 



The biosynthetic paths to terpene compounds have been 

 much clarified in recent years by work from the laboratories 

 of Lynen (107), Bloch (108), Folkers (109), and Popjak (110). 

 Successive condensations of acetyl CoA give acetoacetyl CoA 

 and then y8-hydroxy-^-methyl-glutaryl (or crotonyl)-CoA 



60 



