VitaminA 2010 - Vitamin A Functions Vision, cell...

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Vitamin A Functions – Vision, cell development and health, immunity Food sources – Preformed vitamin A: liver, milk, egg yolks – Beta-carotene: yellow/orange fruits and vegetables From: Insel, Turner and Ross; Nutrition, 2nd Edition
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Vitamin A Toxicity – Can be fatal! Deficiency – Eyes, skin and other epithelial tissues
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Vitamin A Vitamin A is a generic term for a group of related compounds. Retinol, retinal, retinoic acid and related compounds collectively known as retinoids . Beta-carotene and other carotenoids that can be converted by the body into retinol are referred to as provitamin A carotenoids.
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Vitamin A or retinol is the immediate precursor to two important active metabolites: 1. Retinal: plays a critical role in vision. 2. Retinoic acid: intracellular messenger that affects transcription of a number of genes. Vitamin A does not occur in plants, but many plants contain carotenoids such as beta-carotene that can be converted to vitamin A within the intestine and other tissues
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All- trans -retinol All- trans -retinal Retinoic acid The Retinoids OH
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Photosensitive cells on the retina are Rods and Cones Vitamin A and vision www. retinaaustralia .com.au/ eye_anatomy . htm
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http://porpax.bio.miami.edu/~cmallery/150/neuro/sf43x9ab.jpg
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The visual cycle When light passes through the lens, it is sensed by the retina and converted to a nerve impulse for interpretation by the brain. Retinol is transported to the retina via the circulation, where it moves into retinal pigment epithelial cells. Retinol is esterified to form a retinyl ester, which can be stored. When needed, retinyl esters are hydrolyzed and isomerized to form 11- cis retinol and oxidized to form 11- cis retinal which binds to opsin to form rhodopsin. Rhodopsin can absorb of a photon of light inducing isomerization of 11- cis retinal to all- trans retinal which results in its release. This isomerization triggers a cascade of events, leading to the generation of an electrical signal to the optic nerve.
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This note was uploaded on 05/07/2010 for the course NUTRI SCI 160 taught by Professor Hellerstein during the Spring '10 term at University of California, Berkeley.

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VitaminA 2010 - Vitamin A Functions Vision, cell...

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