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Vitamin A
Vitamin A is a fat-soluble vitamin that is an essential nutrient. The term "vitamin A" encompasses a group of chemically related organic compounds that includes retinol, retinyl esters, and several provitamin (precursor) carotenoids, most notably Β-Carotene, β-carotene (''beta''-carotene). Vitamin A has multiple functions: growth during embryo development, maintaining the immune system, and healthy vision. For aiding vision specifically, it combines with the protein opsin to form rhodopsin, the light-absorbing molecule necessary for both low-light (scotopic vision) and color vision. Vitamin A occurs as two principal forms in foods: A) retinoids, found in Animal source foods, animal-sourced foods, either as retinol or bound to a fatty acid to become a retinyl ester, and B) the carotenoids Α-Carotene, α-carotene (''alpha''-carotene), β-carotene, Γ-Carotene, γ-carotene (''gamma''-carotene), and the xanthophyll beta-cryptoxanthin (all of which contain β-ionone rings) that ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Retinol
Retinol, also called vitamin A1, is a fat-soluble vitamin in the vitamin A family that is found in food and used as a dietary supplement. Retinol or other forms of vitamin A are needed for vision, cellular development, maintenance of skin and mucous membranes, immune function and reproductive development. Dietary sources include fish, dairy products, and meat. As a supplement it is used to treat and prevent vitamin A deficiency, especially that which results in xerophthalmia. It is taken by mouth or by intramuscular injection, injection into a muscle. As an ingredient in skin-care products, it is used to reduce wrinkles and other effects of skin aging. Retinol at normal doses is well tolerated. High doses may cause hepatomegaly, enlargement of the liver, dry skin, and hypervitaminosis A. High doses during pregnancy may harm the fetus. The body converts retinol to retinal and retinoic acid, through which it acts. Retinol was discovered in 1909, isolated in 1931, and first m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vitamer
A vitamer () is any of the related forms in which some vitamin occurs. Each vitamer of a particular vitamin is a compound that performs the functions of that vitamin and prevents the symptoms of deficiency of the vitamin. Early research identified vitamins by their ability to cure vitamin-specific deficiency diseases. For example, vitamin B1 was first identified as a substance that prevented and treated beriberi. Subsequent nutrition research has revealed that all vitamers exhibit biological activity against their specific vitamin deficiency, although different vitamers exhibit different potencies against those diseases. A set of vitamers with related biological activity are grouped together by a general name, or ''generic descriptor'', that refers to similar compounds with the same vitamin function. For example, ''vitamin A'' is the generic descriptor for the class of vitamin A vitamers which include retinol, retinal, retinoic acid, and provitamin carotenoids such as beta-caro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rhodopsin
Rhodopsin, also known as visual purple, is a protein encoded by the ''RHO'' gene and a G-protein-coupled receptor (GPCR). It is a light-sensitive receptor protein that triggers visual phototransduction in rod cells. Rhodopsin mediates dim light vision and thus is extremely sensitive to light. When rhodopsin is exposed to light, it immediately photobleaches. In humans, it is fully regenerated in about 30 minutes, after which the rods are more sensitive. Defects in the rhodopsin gene cause eye diseases such as retinitis pigmentosa and congenital stationary night blindness. History Rhodopsin was discovered by Franz Christian Boll in 1876. The name rhodopsin derives from Ancient Greek () for "rose", due to its pinkish color, and () for "sight". It was coined in 1878 by the German physiologist Wilhelm Friedrich Kühne (1837–1900). When George Wald discovered that rhodopsin is a holoprotein, consisting of retinal and an apoprotein, he called it opsin, which tod ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carnivore
A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they are predominantly Photosynthesis, photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with c ... whose nutrition and energy requirements are met by eating, consumption of animal tissue (biology), tissues (mainly muscle, adipose tissue, fat and other soft tissues) as food, whether through predation or scavenger, scavenging. Nomenclature Mammal order The technical term for mammals in the order (biology), order Carnivora is ''carnivoran'', and they are so-named because most member species in the group have a carnivorous diet, but the similarity of the name of the order and the name of the diet causes confusion. Many but not all carnivorans are meat eaters; a few, such as the fe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Enzyme
An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different molecules known as product (chemistry), products. Almost all metabolism, metabolic processes in the cell (biology), cell need enzyme catalysis in order to occur at rates fast enough to sustain life. Metabolic pathways depend upon enzymes to catalyze individual steps. The study of enzymes is called ''enzymology'' and the field of pseudoenzyme, pseudoenzyme analysis recognizes that during evolution, some enzymes have lost the ability to carry out biological catalysis, which is often reflected in their amino acid sequences and unusual 'pseudocatalytic' properties. Enzymes are known to catalyze more than 5,000 biochemical reaction types. Other biocatalysts include Ribozyme, catalytic RNA molecules, also called ribozymes. They are sometimes descr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Omnivore
An omnivore () is an animal that regularly consumes significant quantities of both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nutrients and energy of the sources absorbed. Often, they have the ability to incorporate food sources such as algae, fungi, and bacteria into their diet. Omnivores come from diverse backgrounds that often independently evolved sophisticated consumption capabilities. For instance, dogs evolved from primarily carnivorous organisms (Carnivora) while pigs evolved from primarily herbivorous organisms (Artiodactyla). Despite this, physical characteristics such as tooth morphology may be reliable indicators of diet in mammals, with such morphological adaptation having been observed in bears. The variety of different animals that are classified as omnivores can be placed into further sub-categories depending on their feeding behaviors. Frug ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Herbivore
A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat non-vascular autotrophs such as mosses, algae and lichens, but do not include those feeding on decomposed plant matters (i.e. detritivores) or macrofungi (i.e. fungivores). As a result of their plant-based diet, herbivorous animals typically have mouth structures ( jaws or mouthparts) well adapted to mechanically break down plant materials, and their digestive systems have special enzymes (e.g. amylase and cellulase) to digest polysaccharides. Grazing herbivores such as horses and cattles have wide flat- crowned teeth that are better adapted for grinding grass, tree bark and other tougher lignin-containing materials, and many of them evolved rumination or cecotropic behaviors to better extract nutrients from plants. A larg ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ionone
The ionones, from greek ἴον ion "violet", are a series of closely related chemical substances that are part of a group of compounds known as rose ketones, which also includes damascones and damascenones. Ionones are aroma compounds found in a variety of essential oils, including rose oil. β-Ionone is a significant contributor to the aroma of roses, despite its relatively low concentration, and is an important fragrance chemical used in perfumery. The ionones are derived from the degradation of carotenoids. The combination of α-ionone and β-ionone is characteristic of the scent of violets and used with other components in perfumery and flavouring to recreate their scent. The carotenes α-carotene, β-carotene, γ-carotene, and the xanthophyll β- cryptoxanthin, can all be metabolized to β-ionone, and thus have vitamin A activity because they can be converted by plant-eating animals to retinol and retinal. Carotenoids that do not contain the β-ionone moiety c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Xanthophyll
Xanthophylls (originally phylloxanthins) are yellow pigments that occur widely in nature and form one of two major divisions of the carotenoid group; the other division is formed by the carotenes. The name is from Greek: (), meaning "yellow", and (), meaning "leaf"), due to their formation of the yellow band seen in early chromatography of leaf pigments. Molecular structure As both are carotenoids, xanthophylls and carotenes are similar in structure, but xanthophylls contain oxygen atoms while carotenes are ''purely hydrocarbons'', which do not contain oxygen. Their content of oxygen causes xanthophylls to be more polar (in molecular structure) than carotenes, and causes their separation from carotenes in many types of chromatography. (Carotenes are usually more orange in color than xanthophylls.) Xanthophylls present their oxygen either as hydroxyl groups and/or as hydrogen atoms substituted by oxygen atoms when acting as a bridge to form epoxides. Occurrence Like other c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Γ-Carotene
γ-Carotene (''gamma''-carotene) is a carotenoid, and is a biosynthetic intermediate for cyclized carotenoid synthesis in plants. It is formed from cyclization of lycopene by lycopene cyclase epsilon. Along with several other carotenoids, γ-carotene is a vitamer of vitamin A in herbivores and omnivores. Carotenoids with a cyclized, beta-ionone ring can be converted to vitamin A, also known as retinol, by the enzyme beta-carotene 15,15'-dioxygenase; however, the bioconversion of γ-carotene to retinol has not been well-characterized. γ-Carotene has tentatively been identified as a biomarker for green and purple sulfur bacteria in a sample from the 1.640 ± 0.003-Gyr-old Barney Creek Formation in Northern Australia which comprises marine sediments. Tentative discovery of γ-carotene in marine sediments implies a past euxinic environment, where water columns were anoxic and sulfidic. This is significant for reconstructing past oceanic conditions, but so far γ-carotene has only b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Α-Carotene
α-Carotene (''alpha''-carotene) is a form of carotene with a β-ionone ring at one end and an α-ionone ring at the opposite end. It is the second most common form of carotene. Human physiology In American and Chinese adults, the mean concentration of serum α-carotene was 4.71 μg/dL. Including 4.22 μg/dL among men and 5.31 μg/dL among women. * , Tufts Health and Nutrition Letter, March 2011 Dietary sources The following vegetables are rich in alpha-carotene: * Yellow-orange vegetables:Carrot
The carrot ('' Daucus carota'' subsp. ''sativus'') is a ...
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