Vitamin A is an essential human nutrient. Its important part is the retinyl group, which can be found not in a single compound, but in several forms. In foods of animal origin, the major form of vitamin A is an alcohol (retinol), but can also exist as an aldehyde (retinal), or as an acid (retinoic acid). Precursors to the vitamin (provitamins) are present in foods of plant origin as some of the members of the carotenoid family of compounds.[1]
All forms of vitamin A have a Beta-ionone ring to which an isoprenoid chain is attached. This structure is essential for vitamin activity.[1] The orange pigment of carrot - Beta-carotene - can be represented as two connected retinyl groups. Retinyl group, being attached to a protein, is the only primary light absorber in visual perception, and the compound name is related to retina of eye.
Vitamin A may be found in various forms:
retinol, the animal form of vitamin A, is a yellow, fat-soluble, vitamin with importance in vision and bone growth. Since the alcohol form is unstable, the vitamin is usually produced and administered in a form of retinyl acetate or palmitate.
other retinoids, a class of chemical compounds that are related chemically to vitamin A, are used in medicine.
Fresh fruit and vegetables provide fibre and vitamins.2.我建议你在日常饮食中补充些维生素E和维生素A。I suggest supplementing your diet with vitamins E and A.满意请采纳❤。
1. Vegetables contain many vitamins.
2. Many people took part in the
activities, including some of the students
3. Students can have access to the library.
4. ThE reference book is designed for college
students
5. Students are not permitted to play mobile phone in
class.
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vitamin:
Any of various fat-soluble or water-soluble organic substances essential in minute amounts for normal growth and activity of the body and obtained naturally from plant and animal foods.
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