Rhodopsin night blindness

G protein-coupled receptor kinase 1, rhodopsin kinase RHOK/ GRKl) 13q34 Exon 5 deletion Oguchi disease, reces-sively inherited stationary night blindness Impairment of GRKl-mediated desensitization of rhodopsin (189-191)... 

Night Blindness, Retinitis Pigmentosa, and Rhodopsin Phosphorylation... 

A deficiency of vitamin A leads to vision defects, including a visual impairment at low light levels, termed night blindness. For the processes of vision, retinol needs to be converted first by oxidation into the aldehyde retinal, and then by enzymic isomerization to cw-retinal. c -Retinal is then bound to the protein opsin in the retina via an imine linkage (see Section 7.7.1) to give the red visual pigment rhodopsin. 

Vitamin A Precursor to rhodopsin, a chemical used for vision assists in inhibiting bacterial and viral infections Night blindness (retinol)... 

Vitamin A is necessary for growth and reproduction, resistance to infection, maintenance and differentiation of epithelial tissues, stability and integrity of membrane structures, and the process of vision. In terms of the last function, vitamin A is a component of rhodopsin or visual purple, a photosensitive pigment in the eye that is needed for vision in dim light. An early mild clinical symptom of vitamin A deficiency is night blindness a severe deficiency of this fat-soluble vitamin results in xerophthalmia, an eye condition leading to blindness. 

A deficiency causes night blindness, which is considered an early symptom of retinol deficiency. Night blindness refers to decreased ability to see in very dim light because there is an inadequate amount of retinal in the eye to fuUy "stock" the rods with functional rhodopsin. There is some evidence that as retinol levels in the liver decrease, the equilibrium favors the movement of retinol from the eye back to the liver. 

This condition leads to permanent blindness in about half of cases, and many of those affected are preschool children. Night blindness occurs early in vitamin A deficiency. There is a reduction in rhodopsin concentration, followed by retinal degeneration and loss of photoreceptor cells. Degenerative changes may be due to instability of free opsin or may indicate an additional nutritive function for retinaldehyde (or retinoic acid) in retinal cells. The degenerative changes of retinitis pigmentosa, a relatively common, inherited cause of blindness, closely resemble those of vitamin A deficiency. 

The answer is c. (Murray, pp 627-661. Scriver, pp 3897-3964. Sack, pp 121-138. Wilson, pp 287-320.) The retinal pigment rhodopsin is composed of the 11-cis-retinal form of vitamin A coupled to opsin. Light iso-merizes 11-cis-retinal to all-trans-retinal, which is hydrolyzed to free all-trans-retinal and opsin. In order for regeneration of rhodopsin to occur, 11 -cis-retinal must be regenerated. This dark reaction involves the isomerization of all-trans-retinal to 11-cis-retinal, which combines with opsin to reform rhodopsin. A deficiency of vitamin A, which is often derived from the P-carotene of plants, results in night blindness. 

Vitamin A helps maintain the skin and mucous membranes of the oral cavity and the digestive, respiratory, reproductive, and urinary tracts. Vitamin A is also critical for vision. The aldehyde form of Vitamin A, called retinal, binds to a protein called opsin to form the visual pigment rhodopsin. This pigment is found in the rod cells of the retina of the eye. These cells are responsible for black-and-white vision. As you might expect, a deficiency of vitamin A can have terrible consequences. In children, lack of vitamin A leads to xerophthalmia, an eye disease that results first in night blindness and eventually in total blindness. The disease can be prevented by an adequate dietary or supplementary supply of this vitamin. Because vitamin A is stored in the liver, a dose of 0.03 mg will protect a child for six months. Yet in countries that have suffered from cruel famines, even this amount of vitamin A is unavailable, and the burdens of malnutrition and disease lead to total blindness in thousands of children. 

Ans. The disease is called xerophthalmia, or night blindness. It is caused by the insufficient synthesis of the visual pigment rhodopsin. Rhodopsin contains the retinal group, derived from vitamin A. 

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