Chemistry of Vision

FIGURE 17 11 Imine formation between the aldehyde function of 11 as retinal and an ammo group of a protein (opsin) is involved in the chemistry of vision The numbering scheme in retinal is specifically developed for carotenes and related compounds... 

Carotenoids absorb visible light (Section 13 21) and dissipate its energy as heat thereby protecting the organism from any potentially harmful effects associated with sunlight induced photochemistry They are also indirectly involved m the chemistry of vision owing to the fact that p carotene is the biosynthetic precursor of vitamin A also known as retinol a key substance m the visual process... 

Retinoid acid is a transcription factor. Retinoids play significant roles in dermatology, in the prevention of some cancers, and in the chemistry of vision. Consequently, many works have been dedicated to fluorinated analogues of retinoids. 

Ragnar Granit, Haldan Keffer Hartline, and George Wald Physiology/Medicine Chemistry of vision... 

Special Issue on the Chemistry of Vision, Accts. Chem. Res. 8, 81-112 (1975). 

Cis-trans isomerization is an important step in the chemistry of vision, for example, the light-initiated, enzyme-catalyzed isomerization of cis to frans-retinal. 

Beyond its vital importance in the chemistry of vision, cis-trans isomerization offers potential advantages for organized assemblies capable of photoswitching. The latter is frequently a fast process which requires a strictly photochemical... 

The absorption peak of this compound appears at X = 325 nm. This molecule plays an important role in the chemistry of vision. 

One example of this process is found in the chemistry of vision. Ill the rods and cones of the eye, the aldehyde 11 -cis-retinal forms an imine by reaction with an amino group of the protein opsin. Studies have shown that the nitrogen of the imine of the product, called rhodopsin. is protonated. 

Figure 6.7 The rhodopsin-transducin cascade resulting in cGMP hydrolysis. R is rho-dopsin R is "activated rhodopsin" is the transducin ffy-subunit complex Ta is the transducin a subunit. Inset A rod cell showing entry of Na+ ions into the outer segment of the cell through cGMP-sensitive channels and existing from the inner segment via an ATPase pump. (Based, in part, on Lolley RN, Lee RH. Cyclic GMP and photoreceptor function. FASEB J 4 3001-3008, 1990, and partly on Zurer PS. Chemistry of vision. Chem Eng News November, 1983, p. 34.)...

Many imines play vital roles in biological systems. A key molecule in the chemistry of vision is the highly conjugated imine rhodopsin, which is synthesized in the rod cells of the eye from 11-cis-retinal (the molecule introducing Chapter 21) and a 1° amine in the protein opsin. 

The role of rhodopsin in the chemistry of vision (Opener, Section 21.11B)... 

CHEMISTRY WORK Carrots. Alkenes, and the Chemistry of Vision 221... 

Vitamin A performs numenius biochemical functions. It promotes the production nf mucus by the basal cells of the epithelium, whereas in its absence keratin can be fonned. Vitamin A performs a function in the biosynthesis of glycogen and some steroids, and increased quantities nf coen/yme Q are found in the livers nf vitamin-deficicnt rats. Significantly. the best-known action of vitamin A is its function in the chemistry of vision. 

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