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Retinol
IUPAC name (2E,4E,6E,8E)-3,7-dimethyl- 9-(2,6,6-trimethylcyclohex-1-enyl)

nona-2,4,6,8-tetraen-1-ol
Identifiers
CAS number [11103-57-4]
PubChem 1071
SMILES CC(=CC=CC(C)=CCO) C=CC1=C(C)CCCC1(C)C
Properties
Molecular formula C20H30O
Molar mass 286. IUPAC Nomenclature is a system of naming Chemical compounds and of describing the science of Chemistry in general CAS registry numbers are unique numerical identifiers for Chemical compounds Polymers biological sequences mixtures and Alloys They are also referred to PubChem is a Database of chemical Molecules The system is maintained by the National Center for Biotechnology Information (NCBI a component A chemical formula is a way of expressing information about the Atoms that constitute a particular Chemical compound, and how the relationship between those atoms changes Molar mass, symbol M, is the Mass of one mole of a substance ( Chemical element or Chemical compound) 456 g/mol
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references

Retinol (Afaxin), the animal form of vitamin A, is a fat-soluble vitamin important in vision and bone growth. In Chemistry, the standard state of a material is its state at 1 bar (100 Kilopascals exactly Vitamin A refers to a family of similarly shaped molecules the Retinoids. The visual system is the part of the Nervous system which allows organisms to see. Bones are rigid organs that form part of the Endoskeleton of Vertebrates They function to move support and protect the various organs of the body produce It belongs to the family of chemical compounds known as retinoids. The retinoids are a class of Chemical compounds that are related chemically to Vitamin A. Retinol is ingested in a precursor form; animal sources (liver and eggs) contain retinyl esters, whereas plants (carrots, spinach) contain pro-vitamin A carotenoids. The liver is a vital organ in the human body and is present in Vertebrates and some other animals An egg is a round or oval body laid by the female of many animals consisting of an Ovum surrounded by layers of Membranes and an outer casing which acts to nourish Esters are a class of Chemical compounds and Functional groups Esters consist of an inorganic or organic Acid in which at least Plants are living Organisms belonging to the kingdom Plantae. The carrot ( Daucus carota subsp sativus, Etymology: Middle French carotte, from Late Latin carōta, from Greek karōton Spinach ( Spinacia oleracea) is a Flowering plant in the family of Amaranthaceae. Carotenoids are organic Pigments that are naturally occurring in Chromoplasts of plants and some other photosynthetic Organisms Hydrolysis of retinyl esters results in retinol while pro-vitamin A carotenoids can be cleaved to produce retinal. Retinal, technically called retinene1 or retinaldehyde, is a light-sensitive Retinene molecule found in the Photoreceptor cells of Retinal, also known as retinaldehyde, can be reversibly reduced to produce retinol or it can be irreversibly oxidized to produce retinoic acid. The best described active retinoid metabolites are 11-cis-retinal and the all-trans and 9-cis-isomers of retinoic acid.

Contents

Discovery

In 1913, Elmer McCollum, a biochemist at the University of Wisconsin-Madison, and colleague Marguerite Davis identified a fat-soluble nutrient in butterfat and cod liver oil. Elmer McCollum ( March 3, 1879 &ndash November 15, 1967) was an American biochemist Typical biochemists study chemical processes and chemical transformations in living organisms Marguerite Davis ( September 16, 1887 September 1967 was the co-discoverer of Vitamin A and Vitamin B with Elmer Verner McCollum in 1913 Butterfat or milkfat is the Fatty portion of Milk. Milk and cream are often sold according to the amount of butterfat they contain This article is about the fish extract for the traditional Newfoundland song see " Cod Liver Oil (song " Their work confirmed that of Thomas Osborne and Lafayette Mendel, at Yale, which suggested a fat-soluble nutrient in butterfat, also in 1913. Lafayette Benedict Mendel ( February 5, 1872 &ndash December 9, 1935) was an American Biochemist known for his work in [1] Vitamin A was first synthesized in 1947 by two Dutch chemists, David Adriaan van Dorp and Jozef Ferdinand Arens. David 'Davy' Adriaan van Dorp ( Amsterdam April 27 1915 - Vlaardingen February 19 1995) was a Dutch Chemist

Chemical structure and function

Many different geometric isomers of retinol, retinal and retinoic acid are possible as a result of either a trans or cis configuration of four of the five double bonds found in the polyene chain. Polyenes are poly- unsaturated Organic compounds that contain one or more sequences of alternating double and single Carbon -carbon bonds The cis isomers are less stable and can readily convert to the all-trans configuration (as seen in the structure of all-trans-retinol shown here). Nevertheless, some cis isomers are found naturally and carry out essential functions. For example, the 11-cis-retinal isomer is the chromophore of rhodopsin, the vertebrate photoreceptor molecule. A chromophore is part (or moiety) of a Molecule responsible for its Color. Rhodopsin, also known as visual purple, is a Pigment of the Retina that is responsible for both the formation of the Photoreceptor cells and the Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes Photoreceptor can refer to In anatomy/cell biology Photoreceptor cell: a photosensitive cell most commonly referring to a specialized type of neuron Rhodopsin is comprised of the 11-cis-retinal covalently linked via a Schiff base to the opsin protein (either rod opsin or blue, red or green cone opsins). Schiff base (or azomethine) named after Hugo Schiff, is a Functional group that contains a Carbon - Nitrogen Double bond Opsins are a group of light-sensitive 35-55 kDa membrane-bound G protein-coupled receptors of the Retinylidene protein family found in Photoreceptor cells The process of vision relies on the light-induced isomerisation of the chromophore from 11-cis to all-trans resulting in a change of the conformation and activation of the photoreceptor molecule. One of the earliest signs of vitamin A deficiency is night-blindness followed by decreased visual acuity.

George Wald won the 1967 Nobel Prize in Physiology or Medicine for his work with retina pigments (also called visual pigments), which led to the understanding of the role of vitamin A in vision. George Wald ( November 18, 1906 &ndash April 12, 1997) was an American Scientist who is best known for his work with pigments Year 1967 ( MCMLXVII) was a Common year starting on Sunday (link will display full calendar of the 1967 Gregorian calendar. The Nobel Prize in Physiology or Medicine (Nobelpriset i fysiologi eller medicin is awarded once a year by the Swedish Karolinska Institute. The vertebrate retina is a light sensitive part inside the inner layer of the Eye.

Many of the non-visual functions of vitamin A are mediated by retinoic acid, which regulates gene expression by activating intracellular retinoic acid receptors. The retinoic acid receptor (RAR is a type of Nuclear receptor which is activated by both All-trans retinoic acid and 9-cis retinoic acid. The non-visual functions of vitamin A are essential in the immunological function, reproduction and embryonic development of vertebrates as evidenced by the impaired growth, susceptibility to infection and birth defects observed in populations receiving suboptimal vitamin A in their diet.

Role in embryology

Retinoic acid via the retinoic acid receptor influences the process of cell differentiation, hence, the growth and development of embryos. During development there is a concentration gradient of retinoic acid along the anterior-posterior (head-tail) axis. Cells in the embryo respond differently to retinoic acid depending on the amount present. For example, in vertebrates the hindbrain transiently forms eight rhombomers and each rhombomere has a specific pattern of genes being expressed. If retinoic acid is not present the last four rhombomeres do not develop. Instead rhombomeres 1-4 grow to cover the same amount of space as all eight would normally occupy. Retinoic acid has its effects by turning on a differential pattern of Hox genes which encode different homeodomain transcription factors which in turn can turn on cell type specific genes. Deletion of the Hox-1 gene from rhombomere 4 makes the neurons growing in that region behave like neurons from rhombomere 2. The retina is also patterned by retinoic acid, with a concentration gradient that is high on the ventral side of the retina and low on the dorsal side.

Stem cell biology

Retinoic acid is an influential factor used in differentiation of stem cells to more committed fates, echoing retinoic acid's importance in natural embryonic developmental pathways. It is thought to initiate differentiation into a number of different cell lineages by unsequestering certain sequences in the genome.

It has numerous applications in a plethora of stem cell differentiation protocols; amongst these are the differentiation of human embryonic stem cells to posterior foregut lineages and also to functional motor neurons. Embryonic stem cells (ES cells are Stem cells derived from the inner cell mass of an early stage Embryo known as a Blastocyst. In Vertebrates the term motor neuron (or motoneuron) classically applies to Neurons located in the Central nervous system (or CNS that project

Vision

Main article: visual cycle

Vitamin A is required in the production of rhodopsin, the visual pigment used in low light levels. Visual phototransduction is a process by which Light is converted into Electrical signals in the Rod cells Cone cells and Photosensitive ganglion Rhodopsin, also known as visual purple, is a Pigment of the Retina that is responsible for both the formation of the Photoreceptor cells and the Ommochrome (or visual pigment) refers to several biological Pigments that occur in the Eyes of Crustaceans and Insects The This is why eating foods rich in vitamin A is said to allow an individual to see in the dark.

Epithelial Cells

Vitamin A is essential for the correct functioning of epithelial cells. In biology and medicine epithelium is a tissue composed of cells that line the cavities and surfaces of structures throughout the body In Vitamin A deficiency, mucus-secreting cells are replaced by keratin producing cells, leading to xerosis. Keratins are a family of fibrous structural proteins; tough and insoluble they form the hard but nonmineralized structures found in Reptiles Birds Xerosis is the Medical term for dry Skin. It can have many different causes including general Dehydration, Vitamin A deficiency and Diabetes

Glycoprotein synthesis

Glycoprotein synthesis requires adequate Vitamin A status. Not to be confused with Peptidoglycan. Glycoproteins are proteins that contain Oligosaccharide chains ( Glycans) covalently attached In severe Vitamin A deficiency, lack of glycoproteins may lead to corneal ulcers or liquefaction.

Immune System

Vitamin A is essential to maintain intact epithelial tissues as a physical barrier to infection; it is also involved in maintaining a number of immune cell types from both the innate and acquired immune systems. In biology and medicine epithelium is a tissue composed of cells that line the cavities and surfaces of structures throughout the body These include the lymphocytes (B-cells, T-cells, and natural killer cells), as well as many myelocytes (neutrophils, macrophages, and myeloid dendritic cells). A lymphocyte is a type of White blood cell in the Vertebrate Immune system. B cells are Lymphocytes that play a large role in the humoral immune response (as opposed to the cell-mediated immune response, which is governed by T cells belong to a group of White blood cells known as Lymphocytes, and play a central role in Cell-mediated immunity. Natural killer cells (or NK cells) are a type of Cytotoxic Lymphocyte that constitute a major component of the Innate immune system. Neutrophil granulocytes, generally referred to as neutrophils, are the most abundant type of White blood cells in humans and form an essential part of the Macrophages ( Greek: "big eaters" from makros "large" + phagein "eat" ( Mø) are cells within the tissues that Dendritic cells (DCs are Immune cells and form part of the Mammalian Immune system.

Formation of red blood cells (Haematopoiesis)

Vitamin A may be needed for normal haematopoiesis; deficiency causes abnormalities in iron metabolism. Haematopoiesis (from Ancient Greek haima blood poiesis to make (or hematopoiesis in the United States sometimes also haemopoiesis or Human iron metabolism is the set of chemical reactions maintaining Human homeostasis of Iron.

Growth

Vitamin A affects the production of human growth hormone. Growth hormone ( GH) is a Peptide hormone that stimulates growth and cell reproduction in humans and other animals

Clinical use

Main article: Tretinoin

All retinoid forms of vitamin A are used in cosmetic and medical applications applied to the skin. Tretinoin is the acid form of Vitamin A and so also known as all-trans retinoic acid or ATRA. Retinoic acid, termed Tretinoin in clinical usage, is used in the treatment of acne and keratosis pilaris in a topical cream. Tretinoin is the acid form of Vitamin A and so also known as all-trans retinoic acid or ATRA. Acne vulgaris (commonly called acne) is a Skin disease caused by changes in the Pilosebaceous units (skin structures consisting of a Hair follicle Keratosis pilaris (KP also follicular keratosis is a very common genetic follicular condition that is manifested by the appearance of rough bumps on the skin An isomer of tretinoin, isotretinoin is also used orally (under the trade names Accutane and Roaccutane), generally for severe or recalcitrant acne. Isotretinoin ( INN) (aɪsoʊtrɨˈtɪnoʊɨn or /ˌaɪsoʊtrɨˈtɪnoʊɨn/ is a Medication used for the treatment of severe acne. Isotretinoin ( INN) (aɪsoʊtrɨˈtɪnoʊɨn or /ˌaɪsoʊtrɨˈtɪnoʊɨn/ is a Medication used for the treatment of severe acne.

In cosmetics, vitamin A derivatives are used as anti-aging chemicals- vitamin A is absorbed through the skin and increases the rate of skin turnover, and gives an increase in collagen giving a more youthful appearance[2]

Tretinoin, under the alternative name of all-trans retinoic acid (ATRA), is used as chemotherapy for acute promyelocytic leukemia, a subtype of acute myelogenous leukemia. Anti-aging creams are moisturisers marketed with the promise of making the consumer look younger and reducing visible Wrinkles on Collagen is the main Protein of Connective tissue in Animals and the most abundant protein in Mammals making up about 50% of the whole-body protein Acute promyelocytic leukemia is a subtype of Acute myelogenous leukemia (AML a Cancer of the Blood and Bone marrow. Acute myeloid leukemia ( AML) also known as acute myelogenous leukemia, is a Cancer of the Myeloid line of White blood cells characterized This is because cells of this subtype of leukemia are sensitive to agonists of the retinoic acid receptors (RARs).

Units of measurement

When referring to dietary allowances or nutritional science, retinol is usually measured in international units (IU). Nutrition (also called nourishment or aliment) is the provision to cells and Organisms of the materials necessary (in the form of food to support In Pharmacology, the International Unit is a unit of measurement for the amount of a substance based on measured Biological activity or effect IU refers to biological activity and therefore is unique to each individual compound, however 1 IU of retinol is equivalent to approximately 0. 3 micrograms (300 nanograms).

Nutrition

Vitamin properties
Solubility Fat
RDA (adult male) 900 µg/day
RDA (adult female) 700 µg/day
RDA upper limit (adult male) 3,000 µg/day
RDA upper limit (adult female) 3,000 µg/day
Deficiency symptoms
Excess symptoms
Common sources

This vitamin plays an essential role in vision, particularly night vision, normal bone and tooth development, reproduction, and the health of skin and mucous membranes (the mucus-secreting layer that lines body regions such as the respiratory tract). Solubility is the characteristic Physical property referring to the ability of a given substance the Solute, to dissolve in a Solvent. The Dietary Reference Intake (or DRI is a system of Nutrition recommendations from the Institute of Medicine (IOM of the US National Academy of Sciences In the Metric system, a microgram is 1/1000000 of a Gram (1 × 10-6 or 1/1000 of a milligram is one of the smallest units of weight/mass commonly used In the Metric system, a microgram is 1/1000000 of a Gram (1 × 10-6 or 1/1000 of a milligram is one of the smallest units of weight/mass commonly used In the Metric system, a microgram is 1/1000000 of a Gram (1 × 10-6 or 1/1000 of a milligram is one of the smallest units of weight/mass commonly used In the Metric system, a microgram is 1/1000000 of a Gram (1 × 10-6 or 1/1000 of a milligram is one of the smallest units of weight/mass commonly used Nyctalopia (Greek for " night blindness " is a condition making it difficult or impossible to see in relatively low light Keratomalacia is an Eye disorder that leads to a dry Cornea. One of its major causes is a deficiency of Vitamin A. Teratology stems from the Greek ( Genitive) meaning monster, or marvel and, meaning word, speech. Osteoporosis is a Disease of Bone that leads to an increased risk of fracture. The liver is a vital organ in the human body and is present in Vertebrates and some other animals Dairy products are generally defined as Foodstuffs produced from Milk. The term fruit has different meanings dependent on context and the term is not synonymous in Food preparation and Biology. Leaf vegetables, also called potherbs, greens, or leafy greens, are plant leaves eaten as a Vegetable, sometimes accompanied Vitamin A also acts in the body as an antioxidant, a protective chemical that may reduce the risk of certain cancers.

There are two sources of dietary vitamin A. Active forms, which are immediately available to the body are obtained from animal products. These are known as retinoids and include retinal and retinol. Precursors, also known as provitamins, which must be converted to active forms by the body, are obtained from fruits and vegetables containing yellow, orange and dark green pigments, known as carotenoids, the most well-known being beta-carotene. For this reason, amounts of vitamin A are measured in Retinal Equivalents (RE). One RE is equivalent to 0. 001 mg of retinal, or 0. 006 mg of beta-carotene, or 3. 3 International Units of vitamin A.

In the intestine, vitamin A is protected from being chemically changed by vitamin E. Vitamin A is fat-soluble and can be stored in the body. Most of the vitamin A you eat is stored in the liver. When required by a particular part of the body, the liver releases some vitamin A, which is carried by the blood and delivered to the target cells and tissues.

Dietary intake

The Dietary Reference Intake (DRI) Recommended Daily Amount (RDA) for Vitamin A for a 25-year old male is 900 micrograms/day, or 3000 IU. The Dietary Reference Intake (or DRI is a system of Nutrition recommendations from the Institute of Medicine (IOM of the US National Academy of Sciences

The Food Standards Agency states that an average adult should not consume more than 1500 micrograms (5000 IU) per day, because this increases the chance of osteoporosis. The Food Standards Agency is a Non-ministerial government department of the Government of the United Kingdom. Osteoporosis is a Disease of Bone that leads to an increased risk of fracture.

During the absorption process in the intestines, retinol is incorporated into chylomicrons as the ester form, and it is these particles that mediate transport to the liver. In Anatomy, the intestine is the segment of the alimentary canal extending from the Stomach to the Anus and in humans and other mammals consists Chylomicrons are large lipoprotein particles that transport dietary lipids from the intestines to other locations in the body The liver is a vital organ in the human body and is present in Vertebrates and some other animals Liver cells (hepatocytes) store vitamin A as the ester, and when retinol is needed in other tissues, it is de-esterifed and released into the blood as the alcohol. Hepatocytes make up 70-80% of the Cytoplasmic mass of the Liver. Retinol then attaches to a serum carrier, retinol binding protein, for transport to target tissues. Retinol binding proteins are a family of Proteins with diverse functions A binding protein inside cells, cellular retinoic acid binding protein, serves to store and move retinoic acid intracellularly. Not to be confused with Intercellular, meaning "between cells" Carotenoid bioavailability ranges between 1/5 to 1/10 of retinol's. In Pharmacology, bioavailability is used to describe the fraction of an administered Dose of unchanged drug that reaches the Systemic circulation, one of Carotenoids are better absorbed when ingested as part of a fatty meal. Also, the carotenoids in vegetables, especially those with tough cell walls (e. g. carrots), are better absorbed when these cell walls are broken up by cooking or mincing.

Deficiency

see Vitamin A deficiency for details
Prevalence of vitamin A deficiency. Source: WHO
Prevalence of vitamin A deficiency. Vitamin A deficiency is common in developing countries but rarely seen in developed countries Source: WHO

Vitamin A deficiency is common in developing countries but rarely seen in developed countries. Approximately 250,000 to 500,000 malnourished children in the developing world go blind each year from a deficiency of vitamin A. Night blindness is one of the first signs of vitamin A deficiency. Nyctalopia (Greek for " night blindness " is a condition making it difficult or impossible to see in relatively low light Vitamin A deficiency contributes to blindness by making the cornea very dry and damaging the retina and cornea. The cornea is the transparent front part of the Eye that covers the iris, Pupil, and Anterior chamber. The vertebrate retina is a light sensitive part inside the inner layer of the Eye.

Retinoid overdose (toxicity)

see Hypervitaminosis A for details

The Tolerable Upper Intake Level (UL) for vitamin A, for a 25-year old male, is 3,000 micrograms/day, or about 10,000 IU. Hypervitaminosis A refers to the effects of excessive Vitamin A (specifically retinoid intake The Dietary Reference Intake (or DRI is a system of Nutrition recommendations from the Institute of Medicine (IOM of the US National Academy of Sciences

Too much vitamin A in retinoid form can be harmful or fatal, resulting in what is known as hypervitaminosis A. The body converts the dimerized form, carotene, into vitamin A as it is needed, therefore high levels of carotene are not toxic compared to the ester (animal) forms. The term carotene is used for several related substances having the formula C40H56 The livers of certain animals, especially those adapted to polar environments, often contain amounts of vitamin A that would be toxic to humans. Thus, vitamin A toxicity is typically reported in Arctic explorers and people taking large doses of synthetic vitamin A. The first documented death due to vitamin A poisoning was Xavier Mertz, a Swiss scientist who died in January 1913 on an Antarctic expedition that had lost its food supplies and fell to eating its sled dogs. Xavier Guillaume Mertz (1883-1913 was a Swiss explorer principally famous for his adventures in the Antarctic. Switzerland (English pronunciation; Schweiz Swiss German: Schwyz or Schwiiz Suisse Svizzera Svizra officially the Swiss Confederation Mertz consumed lethal amounts of vitamin A by eating the dogs' livers. [3]

If eaten in one meal, 30 to 90 grams of polar bear liver is enough to kill a human being, or to make even sled dogs very ill. The polar bear ( Ursus maritimus) is a Bear native to the Arctic Ocean and its surrounding seas [4]

Excess vitamin A has also been suspected to be a contributor to osteoporosis. Osteoporosis is a Disease of Bone that leads to an increased risk of fracture. This seems to happen at much lower doses than those required to induce acute intoxication. Only preformed vitamin A can cause these problems, because the conversion of carotenoids into vitamin A is downregulated when physiological requirements are met. An excessive uptake of carotenoids can, however, cause carotenosis. Carotenosis, or carotenosis cutis, is a benign yellowing of the skin in fair skinned humans caused by high dietary uptake of Carotenoids.

The carotenoid beta carotene was interestingly associated with an increase in lung cancer when it was studied in a lung cancer prevention trial in male smokers. Beta-carotene is an Organic compound - a Terpenoid, a red-orange pigment abundant in plants and fruits Lung cancer is a Disease of uncontrolled Cell growth in tissues of the Lung. In non-smokers, the opposite effect has been noted.

Excess preformed vitamin A during early pregnancy has also been associated with a significant increase in birth defects. [5] These defects may be severe, even life-threatening. Even twice the daily recommended amount can cause severe birth defects. [6] The FDA currently recommends that pregnant women get their Vitamin A from foods containing beta carotene and that they should ensure that they consume no more than 5,000 IU of preformed Vitamin A (if any) per day. Although Vitamin A is necessary for fetal development, most women carry stores of Vitamin A in their fat cells, so oversupplementation should be strictly avoided.

A review of all randomized controlled trials in the scientific literature by the Cochrane Collaboration published in JAMA in 2007 found that vitamin A significantly increased mortality by 16% (Relative Risk 1. The Cochrane Collaboration is a group of over 11500 volunteers in more than 90 countries who apply a rigorous systematic process to review the effects of interventions tested in biomedical JAMA The Journal of the American Medical Association is an international peer-reviewed general Medical journal, published 48 times per year by the American 16, 95% confidence interval 1. 10-1. 24). [7]

Sources

All sources of vitamin A can provide retinol, but retinoids are found naturally in some foods of animal origin. Vitamin A refers to a family of similarly shaped molecules the Retinoids. Each of the following contains at least 0. 15 mg of retinoids per 1. 75-7 oz. (50-200 g):

Synthetic Sources

Synthetic retinol is marketed under the following trade names: Acon, Afaxin, Agiolan, Alphalin, Anatola, Aoral, Apexol, Apostavit, Atav, Avibon, Avita, Avitol, Axerol, Dohyfral A, Epiteliol, Nio-A-Let, Prepalin, Testavol, Vaflol, Vi-Alpha, Vitpex, Vogan, and Vogan-Neu. This article is about the fish extract for the traditional Newfoundland song see " Cod Liver Oil (song " Butter is a Dairy product made by churning fresh or fermented Cream or Milk. The liver is a vital organ in the human body and is present in Vertebrates and some other animals An egg is a round or oval body laid by the female of many animals consisting of an Ovum surrounded by layers of Membranes and an outer casing which acts to nourish In Chemistry, chemical synthesis is purposeful execution of Chemical reactions in order to get a product, or several products

Night vision

Night blindness—the inability to see well in dim light—is associated with a deficiency of vitamin A. Vitamin A refers to a family of similarly shaped molecules the Retinoids. At first, the most light sensitive (containing more retinal) protein rhodopsin is influenced. Rhodopsin, also known as visual purple, is a Pigment of the Retina that is responsible for both the formation of the Photoreceptor cells and the Less pigmented by retinal iodopsins (three forms/colors in humans), responsible for color vision and sensing relatively high light intensities (day vision), are less impaired at early stages of the vitamin A deficiency. Photopsins (also known as iodopsins) are the Photoreceptor proteins found in the Cone cells of the Retina that are the basis of Color Color vision is the capacity of an organism or machine to distinguish objects based on the Wavelengths (or frequencies) of the Light they reflect or emit Vitamin A refers to a family of similarly shaped molecules the Retinoids. All these protein-pigment complexes are located in the light-sensing cells in eye's retina. The vertebrate retina is a light sensitive part inside the inner layer of the Eye.

When stimulated by light, rhodopsin splits into a protein and a cofactor: opsin and all-trans-retinal (a form of vitamin A). The regeneration of active rhodopsin requires opsin and 11-cis-retinal. The regeneration of 11-cis-retinal occurs in vertebrates via a sequence of chemical transformations that constitute "the visual cycle" and which occurs primarily in the retinal pigmented epithelial cells.

Without adequate amounts of retinal, regeneration of rhodopsin is incomplete and night blindness occurs. Since carrots are a good source of beta-carotene, there is truth in the old belief that carrots help you see better in the dark.

Closely related chemicals

Genetically engineered vitamin A enriched rice

Due to the high prevalence of vitamin A deficiency in developing countries, there are efforts to produce genetically modified rice rich in beta carotene. Tretinoin is the acid form of Vitamin A and so also known as all-trans retinoic acid or ATRA. Isotretinoin ( INN) (aɪsoʊtrɨˈtɪnoʊɨn or /ˌaɪsoʊtrɨˈtɪnoʊɨn/ is a Medication used for the treatment of severe acne. Developing countries are countries that haven't reached Western-style standards of democratic government free market economy industrialization social programs and human rights guaranties Genetic engineering, Recombinant DNA technology, genetic modification/manipulation (GM and gene splicing are terms that apply to the direct The idea is that this would help poor people, who can not afford a varied diet containing sufficient natural sources of vitamin A, meet their dietary needs. The golden rice project is one such effort, and is already undergoing trials. Golden rice is a variety of Rice ( Oryza sativa) produced through Genetic engineering to biosynthesize Beta-carotene, a precursor of

References

  1. ^ Semba RD. Vitamin A as "Anti-Infective" Therapy, 1920–1940. Journal of Nutrition. 1999;129:783-791. PMID 10203551. Full Text Available
  2. ^ Archives of Dermatology
  3. ^ An account of Mertz's illness, retrieved 20 June 2007.
  4. ^ A. Aggrawal, Death by Vitamin A
  5. ^ Challem, Jack, Caution Urged With Vitamin A in Pregnancy: But Beta-Carotene is Safe, The Nutrition Reporter Newsletter, 1995, retrieved 20 June 2007.
  6. ^ Stone, Brad. Vitamin A and Birth Defects, 6 October 1995, retrieved 20 June 2007.
  7. ^ Bjelakovic et al. , Mortality in randomized trials of antioxidant supplements for primary and secondary prevention: Systematic review and meta-analysis, JAMA, 297:842; February 28, 2007.

External links

Oregon State University ( OSU) is a Coeducational public Research[[ university]] located in Corvallis, Oregon, United

Dictionary

retinol

-noun

  1. A fat-soluble carotenoid vitamin (vitamin A), present in fish oils and green vegetables, essential to normal vision and to bone development.
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