THE MOLECULAR ORGANIZATION OF VISUAL SYSTEMS 



George Wald^ 

 Biological Laboratories of Harvard University, Cambridge, Massachusetts 



Many of the fundamental properties of vision have their source in the 

 physical and chemical properties of retinal molecules. In this paper 

 I shall review briefly the present status of the chemistry of visual 

 excitation, and then examine how this chemistry is reflected in visual 

 performance. 



General Arrangements 



The general organization of visual systems in vertebrate eyes can 

 be stated very simply. The outer segments of the visual receptors, 

 the rods and cones, contain photosensitive pigments, each composed 

 of vitamin A aldehyde (retinene) joined with a specific type of pro- 

 tein called an opsin. There are two vitamins A — ^Ai and Ao — differ- 



CH3 



H 

 C 



CH3 



CH, 



H 

 C 



H2C 



H,C 



/ \ / \ / \ / \ / \ / 



CHoOH 



C< 



C 

 H2 



C 

 H 

 /CH3 



C 

 H 



C 

 H 



Vitamin A,, CHjtCHzOH 

 Rctinenei, C19H27CHO: 



CH3 



i 

 C 



CH, 



H 

 C 



CH, 



C=() 

 \ /H 

 C 

 H 



CH3 



H 

 C 



HC 



\ / \ / \ / \ 



C 

 H 



C 

 H 



C CHjOH 



H 



I /CII, 



HC C< 



c 



CH, 



Vitamin Aj, CiglhiClhOU 

 Retinene., CsHsiCHO: 



C 



C=() 



C 

 H 



' The experiments from our laboratory have been supported in part with funds 

 from the Rockefeller Foiuidation, the OfTuc of \a\al Research, and tlic Public 

 Healtli Service. 



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