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A Dictionary of Genetics phần 9

Tham khảo tài liệu 'a dictionary of genetics phần 9', ngoại ngữ, ngữ pháp tiếng anh phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | vitamin D receptor VDR 473 Vitamin A of light. See chromatophore colorblindness cone pigment genes CPGs opsin rhodopsin. visual purple See rhodopsin. vitalism a philosophy holding that the phenomena exhibited in living organisms are the result of special forces distinct from chemical and physical ones. See mechanistic philosophy. vital stain a dye used to stain living cells Janus green methylene blue trypan blue etc. . vitamin an organic compound often functioning as a coenzyme that is required in relatively minute amounts in the diet for the normal growth of a given organism. vitamin A a fat-soluble vitamin functioning as a precursor to retinal q.v. and retinoic acid q.v. . Its structure is shown at the top of the page. Vitamin A is generated by the splitting in two of a molecule of beta carotene. See carotenoids. vitamin B complex a family of water-soluble vitamins including thiamin B1 riboflavin B2 nicotinic acid pantothenic acid pyridoxin B6 and cobalamin B12 . vitamin C ascorbic acid an important regulator of the oxidation-reduction state of protoplasm. vitamin D calciferol a fat-soluble vitamin required in man for the prevention of rickets. Its structure is shown below. Vitamin D mediates the absorption o c-----1 I HO-c I I HO Ộ Ĩ H-C----- I HO-Ộ-H I. 1-CH2OH Vitamin C of calcium and phosphorus from the intestine and promotes the mineralization of bone. In humans 7-dehydrocholesterol is secreted at the surface of the skin where it is converted by ultraviolet radiation from sunlight into vitamin D. A 10-minute exposure per week of the upper body to sunlight will provide sufficient vitamin D. Most naturally occurring foods lack vitamin D but saltwater fish are an exception. See cholesterol. vitamin D receptor VDR a protein encoded by a gene on the long arm of human chromosome 12. The gene contains 9 exons and the binding to vitamin D is due to the protein segment encoded by exons 7 8 and 9. Exons 2 and 3 each encode zinc-finger domains and mutations in these .