2007-11-22 12:46:39 · 0 answers · asked by mamalicious 1 in Health ➔ Alternative Medicine
Some vitamins can be 'made' in the body from precursor molecules. For example, the body can convert beta-carotene into vitamin A. The body can make vitamin D from exposure to sunlight by converting cholesterol into vitamin D. So, beta-carotene and cholesterol are examples of vitamin precursors.
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2007-11-22 17:08:43 · answer #1 · answered by Doctor J 7 · 2⤊ 0⤋
Vitamin A Precursor
2016-11-07 03:51:52 · answer #2 · answered by Anonymous · 0⤊ 0⤋
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2016-12-24 02:38:57 · answer #3 · answered by Anonymous · 0⤊ 0⤋
Vitamin A is a general term that refers to fat-soluble compounds that are similar in structure and biologic activity to retinol. Vitamin A also refers to dietary precursors of vitamin A (6,11). The precursors of vitamin A (retinol) are the carotenoids (most commonly beta-carotene). The term retinoid refers to any compound that is structurally similar to retinal (aldehyde), retinol (alcohol), or any other substance that exhibits vitamin A activity (1). Retinoic acid, which is a metabolite of retinal (6), is such a substance that is often studied. Synthetic compounds within the vitamin A family have similar structures as the natural form, but may have few or no functions that the natural vitamin posses (11). Most compounds within the vitamin A family are soluble in fat and essential to numerous processes within the body. There have been several water-soluble retinoids, extracted from plasma, bile, and other tissue (11). For the purposes of this literature review any discussion of vitamin A will focus on those retinoids with fat-soluble properties. The main discussion will involve retinol. Retinol is chemically a "pale yellow crystalline solid" (6). The solid and its metabolites exist in nature as various isomers. The biologic metabolites of retinol are unique in that they contain five conjugated double bonds within their six-carbon ring (B-ionone) and isoform specific side chains (11). The double bonds contribute special properties; for example, the double bonding in retinol plays a unique role in multiple vision processes, which will be discussed in a subsequent section of this review. As mentioned earlier most retinoids are soluble in organic solvents and fat. However, oxidation and polymerization are all detrimental to retinoids; therefore, the compounds must be protected from light, oxygen and high temperature
2016-03-25 22:45:31 · answer #4 · answered by Anonymous · 0⤊ 0⤋