Visual process, biochemistry

Volume 27. Photobiology, ionizing radiations I. Phototropism by K. V. Thimann. II. Biochemistry of visual processes by C. D. B. BamGES. III. Bioiuminescence by F. H. Johnson. IV. Photosensitization by M. I. Simon. V. The effects of ultraviolet radiation and photoreactivation by J. K. Setlow. VI. Phytochrome and photoperiod ism in plants by S. B. Hendricks and H. W. Siegel-MAN. VII. Photosynthesis by L. N. M. Duysens and J. Amesz. VIII. Effects of ionizing radiations on biological macromolecules by P. Alexander and J. T. Lett. Subject index. 

Imine formation occurs in many biochemical reactions because euzymes ofteu use an —NH2 group to react with an aldehyde or ketone. An imine linkage is important in the biochemistry of pyridoxal phosphate (which is related to vitamin B see The Chemistry of. .. box on the next page), and in one step of the reactions that take place during the visual process (see The Photochemistry of Vision, Section 13.9). 

Lead intoxication of the visual system is well known and has been extensively described. Visual processing deficits are generated by a direct action of lead on the visual cortex but lead also induces severe alterations in the physiology, morphology and biochemistry of the photoreceptors in the retina (for a review see Fox, 1992). ERG as well as morphological studies have shown that lead selectively affects rods with little or no effects on cones. Lead also competitively and reversibly inhibited isolated retinal Na,K-ATPase. 

Biochemistry of the Visual Process. The photosensitive pigment of the eye is visual purple or rhodopsin. It consists of the protein opsin and neoretinene b, a stereo isomer of the all-frans-retinene (vitamin A aldehyde). The protein opsin attaches only to this css-isomer to form the chromoprotein. 

Insects are so successful because of their mobility, high reproductive potential, ability to exploit plants as a food resource, and to occupy so many ecological niches. Plants are essentially sessile and can be seen to produce flowers, nector, pollen, and a variety of chemical attractants to induce insect cooperation in cross-pollination. However, in order to reduce the efficiency of insect predation upon them, plants also produce a host of structural, mechanical, and chemical defensive artifices. The most visible chemical defenses are poisons, but certain chemicals, not intrinsically toxic, are targeted to disrupt specific control systems in insects that regulate discrete aspects of insect physiology, biochemistry, and behavior. Hormones and pheromones are unique regulators of insect growth, development, reproduction, diapause, and behavior. Plant secondary chemicals focused on the disruption of insect endocrine and pheromone mediated processes can be visualized as important components of plant defensive mechanisms. 

The standard models described in Section 2.1 are all based on an atomic representation of the molecules, i.e., the atomic centers are explicitly visualized (either as intersection of lines, cylinders, or as spheres). Such representations are necessary for the description of structural and dynamic processes on the smallest scale used in chemistry. They become increasingly confusing when the number of atomic centers increases to more than a few hundred atoms. For such scenarios a reduction of complexity is necessary in order to generate better understanding. Molecular parts are represented by ribbons, arrows, cylinders, spheres, tubes, etc. Such representations are predestined to visualize secondary structure elements of proteins in biochemistry. The protein backbone is drawn as a... 

Cooper, A. and Converse, C.A., Energetics of primary processes in visual exitation photochemistry of rhodopsin in rod outer segment membranes. Biochemistry, 15, 2970, 1976. 

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