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Encyclopedia > Melanin

Broadly, melanin is any of the polyacetylene, polyaniline, and polypyrrole "blacks" and "browns" or their mixed copolymers. The most common form of biological melanin is a polymer of either or both of two monomer molecules: indolequinone, and dihydroxyindole carboxylic acid. Melanin exists in the plant, animal and protista kingdoms, where it serves as a pigment. The presence of melanin in the archaea and bacteria kingdoms is an issue of ongoing debate amongst researchers in the field. Polyacetylene (PA) is conducting polymer of the rigid-rod polymer host family. ... Polyaniline (PANI) is a conducting polymer of the semi-flexible rod polymer family. ... A Polypyrrole (PPy) is a chemical compound formed from a number of connected pyrrole ring structures. ... A heteropolymer, also called a copolymer, is a polymer formed when two different types of monomer are linked in the same polymer chain. ... Biological tissue is a collection of interconnected cells that perform a similar function within an organism. ... A polymer is a substance composed of molecules with large molecular mass composed of repeating structural units, or monomers, connected by covalent chemical bonds. ... In chemistry, a monomer (from Greek mono one and meros part) is a small molecule that may become chemically bonded to other monomers to form a polymer. ... In science, a molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ... Divisions Green algae Chlorophyta Charophyta Land plants (embryophytes) Non-vascular plants (bryophytes) Marchantiophyta—liverworts Anthocerotophyta—hornworts Bryophyta—mosses Vascular plants (tracheophytes) †Rhyniophyta—rhyniophytes †Zosterophyllophyta—zosterophylls Lycopodiophyta—clubmosses †Trimerophytophyta—trimerophytes Pteridophyta—ferns and horsetails Seed plants (spermatophytes) †Pteridospermatophyta—seed ferns Pinophyta—conifers Cycadophyta—cycads Ginkgophyta—ginkgo Gnetophyta—gnetae Magnoliophyta—flowering plants... “Animalia” redirects here. ... Typical phyla Rhodophyta (red algae) Chromista Heterokontophyta (heterokonts) Haptophyta Cryptophyta (cryptomonads) Alveolates Pyrrhophyta (dinoflagellates) Apicomplexa Ciliophora (ciliates) Excavates Euglenozoa Percolozoa Metamonada Rhizaria Radiolaria Foraminifera Cercozoa Amoebozoa Choanozoa Many others; classification varies The Kingdom Protista or Protoctista is one of the commonly recognized biological kingdoms, including all the eukaryotes except for... Ernst Haeckels presentation of a three-kingdom system (Plantae, Protista, Animalia) in his 1866 Generelle Morphologie der Organismen). ... Natural Ultramarine pigment in powdered form. ... Phyla Crenarchaeota Euryarchaeota Korarchaeota Nanoarchaeota Archaea are a major division of microorganisms. ... Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ...

Contents

Melanin in humans

In humans, melanin is found in skin, hair, the pigmented tissue underlying the iris, the medulla and zona reticularis of the adrenal gland, the stria vascularis of the inner ear, and in pigment bearing neurons of certain deep brain nuclei such as the locus ceruleus and the substantia nigra. Melanin is the primary determinant of human skin color. In zootomy and dermatology, skin is the largest organ of the integumentary system made up of multiple layers of epithelial tissues that guard underlying muscles and organs. ... A strand of human hair under magnification Hair is also the name of a musical, see respective articles for the stage production and the movie. ... The human iris The iris is the green/grey/brown area. ... In mammals, the adrenal gland (also known as suprarenal glands) are the triangle-shaped endocrine glands that sit atop the kidneys; their name indicates that position (ad, near or at + renes, kidneys). They are chiefly responsible for regulating the stress response through the synthesis of corticosteroids and catecholamines, including cortisol... The zona reticularis (inner region of the adrenal cortex) secretes and synthesize small amounts of weak androgens, steroids that have masculinizing effects. ... In mammals, the adrenal gland (also known as suprarenal glands) are the triangle-shaped endocrine glands that sit atop the kidneys; their name indicates that position (ad, near or at + renes, kidneys). They are chiefly responsible for regulating the stress response through the synthesis of corticosteroids and catecholamines, including cortisol... The upper portion of the spiral ligament contains numerous capillary loops and small blood vessels, and is termed the stria vascularis. ... The inner ear comprises both: the organ of hearing (the cochlea) and the labyrinth or vestibular apparatus, the organ of balance located in the inner ear that consists of three semicircular canals and the vestibule. ... The Locus ceruleus, also spelled locus caeruleus or locus coeruleus (Latin for the blue spot), is a nucleus in the brain stem responsible for physiological responses to stress and panic. ... The substantia nigra, (Latin for black substance, Soemering) or locus niger is a heterogeneous portion of the midbrain, separating the pes (foot) from the tegmentum (covering), and a major element of the basal ganglia system. ... Human skin color can range from very dark to nearly colorless (appearing pinkish white due to the blood in the skin) in different people. ...


Dermal melanin is produced by melanocytes, which are found in the stratum basale of the epidermis. Although human beings generally possess a similar concentration of melanocytes in their skin, the melanocytes in some individuals and ethnic groups more frequently or less frequently express the melanin-producing genes, thereby conferring a greater or lesser concentration of skin melanin. Some individual animals and humans have very little or no melanin in their bodies, a condition known as albinism. This article or section does not cite its references or sources. ... Stratum germinativum or stratum basale is the layer of keratinocytes that lies at the base of the epidermis immediately above the dermis. ... It has been suggested that this article or section be merged with skin. ... Gene expression (also protein expression or often simply expression) is the process by which a genes information is converted into the structures and functions of a cell. ... For a non-technical introduction to the topic, see Introduction to Genetics. ... Albinism (from Latin albus; extended etymology), more technically hypomelanism or hypomelanosis, is a form of hypopigmentary congenital disorder, characterized by a lack of melanin pigment in the eyes, skin and hair (or more rarely the eyes alone). ...


Because melanin is an aggregate of smaller component molecules, there are a number of different types of melanin with differing proportions and bonding patterns of these component molecules. Both pheomelanin and eumelanin are found in human skin and hair, but eumelanin is the most abundant melanin in humans, as well as the form most likely to be deficient in albinism. A strand of human hair under magnification Hair is also the name of a musical, see respective articles for the stage production and the movie. ... Albinism (from Latin albus; extended etymology), more technically hypomelanism or hypomelanosis, is a form of hypopigmentary congenital disorder, characterized by a lack of melanin pigment in the eyes, skin and hair (or more rarely the eyes alone). ...



Eumelanin polymers have long been thought to comprise numerous cross-linked 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA) polymers; recent research into the electrical properties of eumelanin, however, has indicated that it may consist of more basic oligomers adhering to one another by some other mechanism. Thus, the precise nature of eumelanin's molecular structure is once again the object of study.[citation needed] Eumelanin is found in hair and skin, and colors hair grey, black, yellow, and brown. In humans, it is more abundant in peoples with dark skin. There are 2 different types of eumelanin, which are distinguished from each other by their pattern of polymer bonds. The 2 types are black eumelanin and brown eumelanin. A small amount of black eumelanin in the absence of other pigments causes grey hair. A small amount of brown eumelanin in the absence of other pigments causes yellow (blond) color hair. A polymer is a substance composed of molecules with large molecular mass composed of repeating structural units, or monomers, connected by covalent chemical bonds. ... In chemistry, an oligomer consists of a finite number of monomer units (oligo is Greek for a few), in contrast to a polymer which, at least in principle, consists of an infinite number of monomers. ...


Pheomelanin is also found in hair and skin and is more abundant in lighter skinned humans. Pheomelanin imparts a pink to red hue and, thus, is found in particularly large quantities in red hair. Pheomelanin is particularly concentrated in the lips, nipples, glans of the penis, and vagina. Pheomelanin also may become carcinogenic when exposed to the ultraviolet rays of the sun. Chemically, pheomelanin differs from eumelanin in that its oligomer structure incorporates the amino acid L-cysteine, as well as DHI and DHICA units. The hazard symbol for carcinogenic chemicals in the Globally Harmonized System. ...


Neuromelanin is the dark pigment present in pigment bearing neurons of four deep brain nuclei: the substantia nigra (in Latin, literally "black substance") - Pars Compacta part, the locus ceruleus ("blue spot"), the dorsal motor nucleus of the vagus nerve (cranial nerve X), and the median raphe nucleus of the pons. Both the substantia nigra and locus ceruleus can be easily identified grossly at the time of autopsy due to their dark pigmentation. In humans, these nuclei are not pigmented at the time of birth, but develop pigmentation during maturation to adulthood. Although the functional nature of neuromelanin is unknown in the brain, it may be a byproduct of the synthesis of monoamine neurotransmitters for which the pigmented neurons are the only source. The loss of pigmented neurons from specific nuclei is seen in a variety of neurodegenerative diseases. In Parkinson's disease there is massive loss of dopamine producing pigmented neurons in the substantia nigra. A common finding in advanced Alzheimer's disease is almost complete loss of the norepinephrine producing pigmented neurons of the locus ceruleus. Neuromelanin has been detected in primates and in carnivores such as cats and dogs. The substantia nigra, (Latin for black substance, Soemering) or locus niger is a heterogeneous portion of the midbrain, separating the pes (foot) from the tegmentum (covering), and a major element of the basal ganglia system. ... Latin is an ancient Indo-European language originally spoken in Latium, the region immediately surrounding Rome. ... The Locus ceruleus, also spelled locus caeruleus or locus coeruleus (Latin for the blue spot), is a nucleus in the brain stem responsible for physiological responses to stress and panic. ... The vagus nerve (also called pneumogastric nerve or cranial nerve X) is the tenth of twelve paired cranial nerves, and is the only nerve that starts in the brainstem (within the medulla oblongata) and extends, through the jugular foramen, down below the head, to the abdomen. ... The raphe nucleus (Latin for the bit in a fold or seam) is a moderately sized cluster of neurons found in the brain stem, and releases serotonin to the rest of the brain. ... Position of the pons in the human brain The pons (sometimes pons Varolii after Costanzo Varolio) is a knob on the brain stem. ... The substantia nigra, (Latin for black substance, Soemering) or locus niger is a heterogeneous portion of the midbrain, separating the pes (foot) from the tegmentum (covering), and a major element of the basal ganglia system. ... The Locus ceruleus, also spelled locus caeruleus or locus coeruleus (Latin for the blue spot), is a nucleus in the brain stem responsible for physiological responses to stress and panic. ... Human beings are defined variously in biological, spiritual, and cultural terms, or in combinations thereof. ... In biochemistry, monoamines are a group of organic compounds containing only one amino group. ... Neurotransmitters are chemicals that are used to relay, amplify and modulate electrical signals between a presynaptic and a postsynaptic neuron. ... Neurons (also called nerve cells) are the primary cells of the nervous system. ... Neurons (also called nerve cells) are the primary cells of the nervous system. ... Neurodegenerative disease (Greek νέυρο-, néuro-, nerval and Latin dēgenerāre, to decline or to worsen) is a condition in which cells of the brain and spinal cord are lost. ... Dopamine is a phenethylamine naturally produced by the human body. ... The substantia nigra, (Latin for black substance, Soemering) or locus niger is a heterogeneous portion of the midbrain, separating the pes (foot) from the tegmentum (covering), and a major element of the basal ganglia system. ... Norepinephrine (INN) or noradrenaline (BAN) is a catecholamine and a phenethylamine with chemical formula C8H11NO3. ... The Locus ceruleus, also spelled locus caeruleus or locus coeruleus (Latin for the blue spot), is a nucleus in the brain stem responsible for physiological responses to stress and panic. ... Families 15, See classification A primate is any member of the biological order Primates, the group that contains all the species commonly related to the lemurs, monkeys, and apes, with the latter category including humans. ... This tigers sharp teeth and strong jaws are the classical physical traits expected from carnivorous mammalian predators A carnivore (IPA: ), meaning meat eater (Latin carne meaning flesh and vorare meaning to devour), is an animal that eats a diet consisting mainly of meat, whether it comes from live animals... Binomial name Felis catus Linnaeus, 1758 Synonyms Felis lybica invalid junior synonym The cat (or domestic cat, house cat) is a small carnivorous mammal. ... Trinomial name Canis lupus familiaris The dog (Canis lupus familiaris) is a domestic subspecies of the wolf, a mammal of the Canidae family of the order Carnivora. ...


Melanin in other organisms

Melanins have very diverse roles and functions in various organisms. They can protect microorganism, such as bacteria and fungi, against stresses that involve cell damage by solar UV radiation or generation of reactive oxygen species. These include high temperature as well as chemical (e.g. heavy metals and oxidizing agents), and biochemical (e.g., host defenses against invading microbes) stresses.[1] Therefore, in many pathogenic microbes (for example, in Cryptococcus neoformans) melanins appear to play important roles in virulence and pathogenicity by protecting the microbe against immune responses of its host. A potentially novel role of melanin as a photosynthetic pigment in some fungi, enabling them to capture ionizing radiation and harness its energy for growth has recently been described. [2] In invertebrates, a major aspect of the innate immune defense system against invading pathogens involves melanin. Within minutes after infection, the microbe is encapsulated within melanin (melanization), and the generation of free radical byproducts during the formation of this capsule is thought to aid in their killing.[citation needed] Reactive oxygen species (ROS) include oxygen ions, free radicals and peroxides both inorganic and organic. ... Cryptococcus neoformans is an encapsulated yeastlike fungus that can live in both plants and animals. ... Virulence is either the relative pathogenicity or the relative ability to do damage to the host of an infectious agent. ... Pathogenicity is the ability of an organism to cause disease in another organism. ... Radioactivity may mean: Look up radioactivity in Wiktionary, the free dictionary. ...


Synthetic pathways

The first step of the synthetic pathway for both eumelanins and pheomelanins is mediated by tyrosinase: Tyrosinase (monophenol monooxygenase) (EC 1. ...

Tyrosine → DOPA → dopaquinone

Dopaquinone can combine with cysteine by two pathways to benzothiazines and pheomelanins Cysteine is a naturally occurring, sulfur-containing amino acid that is found in most proteins, although only in small quantities. ...

Dopaquinone + cysteine → 5-S-cysteinyldopa → benzothiazine intermediate → pheomelanin
Dopaquinone + cysteine → 2-S-cysteinyldopa → benzothiazine intermediate → pheomelanin

Alternatively, dopaquinone can be converted to leucodopachrome and follow two more pathways to the eumelanins

Dopaquinone → leucodopachrome → dopachrome → 5,6-dihydroxyindole-2-carboxylic acid → quinone → eumelanin
Dopaquinone → leucodopachrome → dopachrome → 5,6-dihydroxyindole → quinone → eumelanin

Microscopic appearance


Under the microscope melanin is brown, non-refractile and finely granular with individual granules having a diameter of less than 800 nanometers. This differentiates melanin from common blood breakdown pigments which are larger, chunky and refractile and range in color from green to yellow or red-brown. In heavily pigmented lesions, dense aggregates of melanin can obscure histologic detail. A dilute solution of potassium permanganate is an effective melanin bleach. Hemosiderin Image of a kidney viewed under a microscope. ... Potassium permanganate is the chemical compound KMnO4. ...


Melanin deficiency in genetic disorders and disease states

Melanin deficiency has been connected for some time with various genetic abnormalities and disease states.


There are approximately ten different types of oculocutaneous albinism, which is mostly an autosomal recessive disorder. Certain ethnicities have higher incidences of different forms. For example, the most common type, called oculocutaneous albinism type 2 (OCA2), is especially frequent among people of black African descent. It is an autosomal recessive disorder characterized by a congenital reduction or absence of melanin pigment in the skin, hair and eyes. The estimated frequency of OCA2 among African-Americans is 1 in 10,000, which contrasts with a frequency of 1 in 36,000 in white Americans [1]. In some African nations, the frequency of the disorder is even higher, ranging from 1 in 2,000 to 1 in 5,000.[2] Another form of Albinism, the "yellow oculocutaneous albinism", appears to be more prevalent among the Amish, who are of primarily Swiss and German ancestry. People with this IB variant of the disorder commonly have white hair and skin at birth, but rapidly develop normal skin pigmentation in infancy.[3] Young woman with albinism from Malawi. ... A world map showing the continent of Africa Africa is the worlds second-largest and second most-populous continent, after Asia. ... A congenital disorder is a medical condition or defect that is present at or before birth (for example, congenital heart disease). ... Languages Predominantly American English Religions Protestantism (chiefly Baptist and Methodist); Roman Catholicism; Islam Related ethnic groups Sub-Saharan Africans and other African groups, some with Native American groups. ... The Amish (Amisch or Amische) (IPA: ) are an Anabaptist Christian denomination in the United States and Canada (Ontario and Manitoba) that are known for their plain dress and limited use of modern conveniences such as automobiles and electricity. ...


Ocular albinism affects not only eye pigmentation, but visual acuity, as well. People with albinism typically test poorly, within the 20/60 to 20/400 range. Additionally, two forms of albinism, with approximately 1 in 2700 most prevalent among people of Puerto Rican origin, are associated with mortality beyond melanoma-related deaths.

Mortality also is increased in patients with Hermansky-Pudlak syndrome and Chediak-Higashi syndrome. Patients with Hermansky-Pudlak syndrome have a bleeding diathesis secondary to platelet dysfunction and also experience restrictive lung disease (pulmonary fibrosis), inflammatory bowel disease, cardiomyopathy, and renal disease. Patients with Chediak-Higashi syndrome are susceptible to infection and also can develop lymphofollicular malignancy.[4]

The role that melanin deficiency plays in such disorders remains under study.


The connection between albinism and deafness has been well known, though poorly understood, for more than a century-and-a-half. In his 1859 treatise On the Origin of Species, Charles Darwin observed that "cats which are entirely white and have blue eyes are generally deaf"[5]. In humans, hypopigmentation and deafness occur together in the rare Waardenburg's syndrome, predominantly observed among the Hopi in North America. [6] The incidence of albinism in Hopi Indians has been estimated as approximately 1 in 200 individuals. Interestingly, similar patterns of albinism and deafness have been found in other mammals, including dogs and rodents. However, a lack of melanin per se does not appear to be directly responsible for deafness associated with hypopigmentation, as most individuals lacking the enzymes required to synthesize melanin have normal auditory function [7]. Instead the absence of melanocytes in the stria vascularis of the inner ear results in cochlear impairment [8], though why this is is not fully understood. It may be that melanin, the best sound absorbing material known, plays some protective function. Alternately, melanin may affect development, as Darwin suggests. This article discusses the way the word deaf is used and how deafness is perceived by hearing and Deaf communities. ... The 1859 edition of On the Origin of Species First published in 1859, The Origin of Species (full title On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life) by British naturalist Charles Darwin is one of the pivotal... For other people of the same surname, and places and things named after Charles Darwin, see Darwin. ... Waardenburg syndrome is a genetic disorder associated with hearing loss and changes in skin and hair pigmentation. ... This article or section does not cite its references or sources. ... World map showing North America A satellite composite image of North America. ... Melanocytes are cells located in the bottom layer of the skins epidermis. ... The cochlea is the auditory branch of the inner ear. ...


In Parkinson's disease, a disorder that affects neuromotor functioning, there is decreased neuromelanin in the substantia nigra as consequence of specific dropping out of dopaminergic pigmented neurons. This results in diminished dopamine synthesis. While no correlation between race and the level of neuromelanin in the substantia nigra has been reported, the significantly lower incidence of Parkinson's in blacks than in whites has "prompt[ed] some to suggest that cutaneous melanin might somehow serve to protect the neuromelanin in substantia nigra from external toxins."[9]. Also see Nicolaus review article on the function of neuromalanins Dopamine is a phenethylamine naturally produced by the human body. ...


In addition to melanin deficiency, the molecular weight of the melanin polymer may be decreased due to various factors such as oxidative stress, exposure to light, perturbation in its association with melanosomal matrix proteins, changes in pH or in local concentrations of metal ions. A decreased molecular weight or a decrease in the degree of polymerization of ocular melanin has been proposed to turn the normally anti-oxidant polymer into a pro-oxidant. In its pro-oxidant state, melanin has been suggested to be involved in the causation and progression of macular degeneration and melanoma. (Ref: Pigment cell Res. 2001; volume 14: pages 148-154. "Redox regulation in human melanocytes and melanoma") A polymer is a substance composed of molecules with large molecular mass composed of repeating structural units, or monomers, connected by covalent chemical bonds. ... In virology, matrix proteins are structural proteins linking the viral envelope with the virus core. ... The correct title of this article is . ... Pro-oxidants are chemicals that induce oxidative stress, either through creating reactive oxygen species or inhibiting antioxidant systems. ... Listen to this article · (info) · play in browser This audio file was created from an article revision dated 2005-07-19, and may not reflect subsequent edits to the article. ... Melanoma is a malignant tumor of melanocytes. ...


Melanin and human adaptation

Melanocytes insert granules of melanin into specialized cellular vesicles called melanosomes. These are then transferred into the other skin cells of the human epidermis. The melanosomes in each recipient cell accumulate atop the cell nucleus, where they protect the nuclear DNA from mutations caused by the ionizing radiation of the sun's ultraviolet rays. People whose ancestors lived for long periods in the regions of the globe near the equator generally have larger quantities of eumelanin in their skins. This makes their skins brown or black and protects them against high levels of exposure to the sun, which more frequently results in melanomas in lighter skinned people. This article or section is in need of attention from an expert on the subject. ... Melanosome - Cellular A melanosome is a cellular organelle containing melanin, the commonest light-absorbing pigment found in the animal kingdom. ... It has been suggested that this article or section be merged with skin. ... HeLa cells stained for DNA with the Blue Hoechst dye. ... The structure of part of a DNA double helix Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions for the development and function of living organisms. ... Radiation hazard symbol. ... UV redirects here. ... World map showing the equator in red In tourist areas, the equator is often marked on the sides of roads The equator marked as it crosses Ilhéu das Rolas, in São Tomé and Príncipe. ... Melanoma is a malignant tumor of melanocytes. ...


With humans, exposure to sunlight stimulates the liver to produce vitamin D. Because high levels of cutaneous melanin act as a natural sun screen, dark skin can be a risk factor for vitamin D deficiency. The liver is an organ present in vertebrates and some other animals. ... Vitamin D is a fat soluble vitamin that contributes to the maintenance of normal levels of calcium and phosphorus in the bloodstream. ...

In Scotland, which lies at a northern latitude, descendants of the Britons have white skin. When their skin is exposed to the meager sunlight, the scant amount of melanin their skin produces is unable to block the sunlight. Therefore, their bodies are able to make Vitamin D with the help of sunlight. Vitamin D, a vitamin found in fish oil, is necessary to prevent rickets, a bone disease caused by too little calcium. Fish Oil is oil derived from fishes. ... Rickets is a softening of the bones in children potentially leading to fractures and deformity. ... General Name, Symbol, Number calcium, Ca, 20 Chemical series alkaline earth metals Group, Period, Block 2, 4, s Appearance silvery white Standard atomic weight 40. ...

In contrast, in Africa, which is near the equator, humans require intense sunlight to penetrate their dark skin to make Vitamin D. This is all well and good. However, when blacks lived in England during the Industrial Revolution, they were the first to develop symptoms of rickets, such as retarded growth, bowed legs and fractures because not enough sunlight was available.

Fortunately, in 1930, Vitamin D was discovered and dispensed as a supplement to add to the diet. Now many common foods like milk and bread are Vitamin D fortified.

The most recent scientific evidence indicates that all humanity originated in Africa. It is most likely that the first people had relatively large numbers of eumelanin producing melanocytes and, accordingly, darker skin (as displayed by the indigenous people of Africa, today). As some of these original peoples migrated and settled in areas of Asia and Europe, the selective pressure for eumelanin production decreased in climates where radiation from the sun was less intense. Thus variations in genes involved in melanin production began to appear in the population, resulting in lighter hair and skin in humans residing at northern latitudes. Studies have been carried out to determine whether these changes were due to genetic drift or positive selection, perhaps driven by requirement for vitamin D. Of the two common gene variants known to be associated with pale human skin, Mc1r [10] does not appear to have undergone positive selection, while SLC24A5 [11] has. A world map showing the continent of Africa Africa is the worlds second-largest and second most-populous continent, after Asia. ... World map showing the location of Asia. ... World map showing the location of Europe. ... In population genetics, genetic drift is the statistical effect that results from the influence that chance has on the success of alleles (variants of a gene). ... The Melanocortin-1 receptor (Mc1r) is one of the key proteins in hair colour production. ... SLC24A5 (solute carrier family 24, member 5) is a gene that is thought to be one of many genes that control skin pigmentation in humans, and therefore implicated in defining race. ...


As with peoples who migrated northward, those with light skin who migrate southward acclimatize to the much stronger solar radiation. Most people's skin darkens when exposed to UV light, giving them more protection when it is needed. This is the physiological purpose of sun tanning. Dark-skinned people, who produce more skin-protecting eumelanin, are less likely to suffer from sunburn and the development of melanoma, a potentially deadly form of skin cancer, as well as other health problems related to exposure to strong solar radiation, including the photodegradation of certain vitamins such as riboflavins, carotenoids, tocopherol, and folate. Despite the risks, many female teens said in a survey with Seventeen that they look better with a tan and feel healthier, more sophisticated Sun tanning describes a darkening of the skin (especially of fair-skinned individuals) in a natural physiological response stimulated by exposure to ultraviolet radiation from sunshine... Melanoma is a malignant tumor of melanocytes. ... Skin cancer is a malignant growth on the skin which can have many causes. ... Solar irradiance spectrum at top of atmosphere. ... Photodegradation is degradation of a molecule caused by the absorption of photons, particularly those wavelengths found in sunlight, such as infrared radiation, visible light and ultraviolet light. ... Retinol (Vitamin A) For the record label, see Vitamin Records Vitamins are nutrients required in tiny amounts for essential metabolic reactions in the body. ... Riboflavin (E101), also known as vitamin B2, is an easily absorbed micronutrient with a key role in maintaining health in animals. ... The orange ring surrounding Grand Prismatic Spring is due to carotenoid molecules, produced by huge mats of algae and bacteria. ... Tocopherol, or vitamin E, is a fat-soluble vitamin in eight forms that is an important antioxidant. ... Folic acid (the anion form is called folate) is a B-complex vitamin (once called vitamin M) that is important in preventing neural tube defects (NTDs) in the developing human fetus. ...


Higher eumelanin levels also can be a disadvantage, however, beyond a higher disposition toward vitamin D deficiency. Dark skin is a complicating factor in the laser removal of port-wine stains. Effective in treating white skin, lasers generally are less successful in removing port-wine stains in Asians and people of African descent. Higher concentrations of melanin in darker-skinned individuals simply diffuse and absorb the laser radiation, inhibiting light absorption by the targeted tissue. Melanin similarly can complicate laser treatment of other dermatological conditions in people with darker skin. A port-wine stain or naevus flammeus is a vascular birthmark consisting of superficial and deep dilated capillaries in the skin which produce a reddish to purplish discoloration of the skin. ... The term Asian can refer to something or someone from Asia. ...


Freckles and moles are formed where there is a localized concentration of melanin in the skin. They are highly associated with pale skin. Freckles are small brownish spots of melanin on human skin in people of fair complexion, predominantly found on the face. ... Melanocytic naevus A mole, technically known as melanocytic naevus is a small, dark spot on human skin. ...


Melanin in the eyes helps protect them from ultraviolet and high frequency visible light; people with blue eyes are more at risk for sun-related eye problems. Further, the ocular lens yellows with age, providing added protection. However, the lens also becomes more rigid with age, losing most of its accommodation — the ability to change shape to focus from far to near — a detriment due probably to protein crosslinking caused by UV exposure. UV redirects here. ... Light from a single point of a distant object and light from a single point of a near object being brought to a focus by changing the curvature of the lens. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ...


Recent research by J.D. Simon et al. (Pigment Cell Research, 2004, 17: 262-269) suggests that melanin may serve a protective role other than photoprotection. Melanin is able to effectively ligate metal ions through its carboxylate and phenolic hydroxyl groups, in many cases much more efficiently than the powerful chelating ligand ethylenediaminetetraacetate (EDTA). It may thus serve to sequester potentially toxic metal ions, protecting the rest of the cell. This hypothesis is supported by the fact that the loss of neuromelanin observed in Parkinson's disease is accompanied by an increase in iron levels in the brain.


Physical properties and technological applications

Absorption spectrum of melanin


Melanin is a biopolymer and a neuropeptide. Melanins are "rigid-backbone" conductive polymers composed of polyacetylene, polypyrrole, and polyaniline "Blacks" and their mixed copolymers. The simplist melanin is polyacetylene, from which all others derive. Some fungal melanins are pure polyacetylene. This article or section does not adequately cite its references or sources. ... A Neuropeptide is any of the variety of peptides found in neural tissue; e. ... Conductive polymers are organic polymer semiconductors. ... Polyacetylene (PA) is conducting polymer of the rigid-rod polymer host family. ... A Polypyrrole (PPy) is a chemical compound formed from a number of connected pyrrole ring structures. ... Polyaniline (PANI) is a conducting polymer of the semi-flexible rod polymer family. ...


In 1963, DE Weiss and coworkers reported [12] high electrical conductivity in a melanin, iodine-doped and oxidized polypyrrole "Black". They achieved the quite high conductivity of 1 Ohm/cm. A decade later, John McGinness, and coworkers reported a high conductivity "ON" state in a voltage-controlled solid-state threshold switch made with DOPA melanin [13]. Further, this material emitted a flash of light— electroluminescence— when it switched. Melanin also shows negative resistance, a classic property of electronically-active conductive polymers. Likewise, melanin is the best sound-absorbing material known [3] due to strong electron-phonon coupling. This may be related to melanin's presence in the inner ear. A Polypyrrole (PPy) is a chemical compound formed from a number of connected pyrrole ring structures. ... John Edward McGinness, PhD, MD, Pioneer in Organic electronics and Nanotechnology. ... Animation of LCD, both unlit and with electroluminiscent backlight switched on Electroluminescence (EL) is an optical phenomenon and electrical phenomenon where a material emits light in response to an electric current passed through it, or to a strong electric field. ... A VI curve with a negative differential resistance region Negative resistance or negative differential resistance (NDR) is a property of electrical circuit elements composed of certain materials in which, over certain voltage ranges, current is a decreasing function of voltage. ... Conductive polymers are organic polymer semiconductors. ... Normals modes of vibration progression through a crystal. ... The inner ear comprises both: the organ of hearing (the cochlea) and the labyrinth or vestibular apparatus, the organ of balance located in the inner ear that consists of three semicircular canals and the vestibule. ...

Melanin voltage-controlled switch, an "active" organic polymer electronic device from 1974. Now in the Smithsonian.
Melanin voltage-controlled switch, an "active" organic polymer electronic device from 1974. Now in the Smithsonian.

These early discoveries were "lost" until the recent emergence of such melanins in device applications, particularly electroluminescent displays. In 2000, the Nobel Prize in Chemistry was awarded to three scientists for their subsequent 1977 (re)discovery and development of such conductive organic polymers. In an essential reprise of Weiss et al's work, these polymers were oxidized, iodine-doped "polyacetylene black" melanins. There is no evidence the Nobel committee was aware of Weiss et als [14] almost identical prior report of passive high conductivity in iodinated polypyrrole black or of switching and high electrical conductivity in DOPA melanin and related organic semiconductors. The melanin organic electronic device is now in the Smithsonian Institution's National Museum of American History's "Smithsonian Chips" collection of historic solid-state electronic devices. Image File history File linksMetadata Gadget128. ... The Nobel Prizes (Swedish: ) are awards in Physics, Chemistry, Literature, Peace, Physiology or Medicine and Economics. ... Conductive polymers are organic polymer semiconductors. ... Polyacetylene (PA) is conducting polymer of the rigid-rod polymer host family. ... Electrical conductivity or specific conductivity is a measure of a materials ability to conduct an electric current. ... Semiconductors are compounds whose electrical conductivity is midway between that of typical metals and that of insulating compounds. ... The Smithsonian Institution Building or Castle on the National Mall serves as the Institutions headquarters. ... The National Museum of American History is a museum administered by the Smithsonian Institution and located in Washington, D.C., on the National Mall. ... In physics, the solid state is one of the three phases of matter (solid, liquid, and gas). ...


Melanin influences neural activity and mediates the conduction of radiation, light, heat and kinetic energy. As such, it is the subject of intense interest in biotech research and development, most notably in organic electronics (sometimes called "plastic electronics") and nanotechnology, where dopants are used to dramatically boost melanin conductivity. Pyrrole black and acetylene black are the most commonly studied organic semiconductors. The nervous system of an animal coordinates the activity of the muscles, monitors the organs, constructs and processes input from the senses, and initiates actions. ... Biotechnology is technology based on agriculture, food science, and medicine. ... Organic electronics, or plastic electronics, is a branch of electronics that deals with conductive polymers, or plastics. ... Buckminsterfullerene C60, also known as the buckyball, is the simplest of the carbon structures known as fullerenes. ... A dopant, also called doping agent and dope, is an impurity element added to a semiconductor lattice in low concentrations in order to alter the optical/electrical properties of the semiconductor. ... A Polypyrrole (PPy) is a chemical compound formed from a number of connected pyrrole ring structures. ... Polyacetylene (PA) is conducting polymer of the rigid-rod polymer host family. ...


Although synthetic melanin (commonly referred to as BSM, or "black synthetic matter") is made up of 3-6 oligomeric units linked together - the so-called "protomolecule" - there is no evidence that naturally occurring biopolymer (BCM, for "black cell matter") mimics this structure. However, since there is no reason to believe that natural melanin does not belong to the category of the polyarenes and polycationic polyenes, like pyrrol black and acetylene black, it is necessary to review all the chemical and biological analytic data gathered to date in the study of natural melanins (eumelanins, pheomelanins, allomelanins)."[15]


Evidence exists in support of a highly cross-linked heteropolymer bound covalently to matrix scaffolding melanoproteins (Eur. J. Biochem. 1995; 232: 159-164 "Interaction of melanosomal proteins with melanin). It has been proposed that the ability of melanin to act as an antioxidant is directly proportional to its degree of polymerization or molecular weight (Ophthalmic research, 2005, 37: 136-141 "Melanin aggregation and polymerization: possible implications in age related macular degeneration"). Suboptimal conditions for the effective polymerization of melanin monomers may lead to formation of lower-molecular-weight, pro-oxidant melanin that is has been implicated in the causation and progression of macular degeneration and melanoma. (Clinical Cancer Res. 2004; 10: 2581-2583 "Etiologic pathogenesis of melanoma: a unifying hypothesis for the missing attributable risk"). Signaling pathways that upregulate melanization in the retinal pigment epithelium (RPE) also may be implicated in the downregulation of rod outer segment phagocytosis by the RPE. This phenomenon has been attributed in part to foveal sparing in macular degeneration. (Mol. Vis. 2005; 11: 482-490 "Melanization and phagocytosis: implications for age-related macular degeneration). A heteropolymer, also called a copolymer, is a polymer formed when two (or more) different types of monomer are linked in the same polymer chain, as opposed to a homopolymer where only one monomer is used. ... Covalent bonding is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. ... Space-filling model of the antioxidant metabolite glutathione. ... The molecular mass of a substance (less accurately called molecular weight and abbreviated as MW) is the mass of one molecule of that substance, relative to the unified atomic mass unit u (equal to 1/12 the mass of one atom of carbon-12). ... In chemistry, a monomer (from Greek mono one and meros part) is a small molecule that may become chemically bonded to other monomers to form a polymer. ... Listen to this article · (info) · play in browser This audio file was created from an article revision dated 2005-07-19, and may not reflect subsequent edits to the article. ... Melanoma is a malignant tumor of melanocytes. ... Overview of signal transduction pathways In biology, signal transduction refers to any process by which a cell converts one kind of signal or stimulus into another, most often involving ordered sequences of biochemical reactions inside the cell, that are carried out by enzymes and linked through second messengers resulting in... Upregulation is the process by which a cell increases the number of receptors to a given hormone or neurotransmitter to improve its sensitivity to this molecule. ... The retinal pigment epithelium is the pigmented cell layer just outside the neurosensory retina that nourishes retinal visual cells, and is firmly attached to the underlying choroid and overlying retinal visual cells. ... Down regulation is the process by which a cell decreases the number of receptors to a given hormone or neurotransmitter to reduce its sensitivity to this molecule. ... Rod cells, or rods, are photoreceptor cells in the retina of the eye that can function in less intense light than can the other type of photoreceptor, cone cells. ... Phagocytosis is a form of endocytosis wherein large particles are enveloped by the cell membrane of a (usually larger) cell and internalized to form a phagosome, or food vacuole. ... The fovea, a part of the eye, is a spot located in the center of the macula. ... Listen to this article · (info) · play in browser This audio file was created from an article revision dated 2005-07-19, and may not reflect subsequent edits to the article. ...


Skin color-based bias in human societies

Human skin color map. Data for native populations collected by R. Biasutti prior to 1940
Human skin color map. Data for native populations collected by R. Biasutti prior to 1940

When skin pigmentation as a characteristic of race is linked to social status or other human attributes, this phenomenon is known as racialism. Many people and societies overlay racialism with racist perceptions and systems which arbitrarily assign to groups of people a status of inherent superiority or inferiority, privilege or disadvantage based on skin color or racial classification. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Human skin color can range from very dark to nearly colorless (appearing pinkish white due to the blood in the skin) in different people. ... This article concerns the term race as used in reference to human beings. ... This article or section does not adequately cite its references or sources. ... Manifestations Slavery · Racial profiling · Lynching Hate speech · Hate crime · Hate groups Genocide · The Holocaust · Armenian Genocide · Pogrom Ethnocide · Ethnic cleansing · Race war Religious persecution · Gay bashing Blood libel · Black Legend Pedophobia · Ephebiphobia Movements Discriminatory Aryanism · Neo-Nazism · Ku Klux Klan National Party (South Africa) American Nazi Party Kahanism · Supremacism Anti...


Various presumptions are also made about people with regard to hair color. Common stereotypes in the West are dumb blondes, hot-tempered redheads and vixen brunettes. For alternative meanings for The West in the United States, see the U.S. West and American West. ... One of the worlds most famous blondes Marilyn Monroe, who was in fact a natural brunette Blond (feminine, blonde) is a hair colour found in certain mammals characterised by low levels of the dark pigment eumelanin and higher levels of the pale pigment phæomelanin, in common with red... Female with red hair Male with red hair Red hair (also referred to as auburn, ginger, or titian) varies from a deep red through to bright copper. ... Brunette is the feminine of French brunet, which is a diminutive of brun, brune, meaning brown or dark-haired, ultimately from Latin BRVNVS (brown). ...


See also

Carotene is responsible for the orange colour of the carrots and many other fruits and vegetables. ... Human skin color can range from very dark to nearly colorless (appearing pinkish white due to the blood in the skin) in different people. ... SLC24A5 (solute carrier family 24, member 5) is a gene that is thought to be one of many genes that control skin pigmentation in humans, and therefore implicated in defining race. ... The Melanocortin-1 receptor (Mc1r) is one of the key proteins in hair colour production. ... Melanistic Eastern Grey Squirrel in Toronto, Canada. ... Melanoma is a malignant tumor of melanocytes. ... Semiconductors are compounds whose electrical conductivity is midway between that of typical metals and that of insulating compounds. ... Manifestations Slavery · Racial profiling · Lynching Hate speech · Hate crime · Hate groups Genocide · The Holocaust · Armenian Genocide · Pogrom Ethnocide · Ethnic cleansing · Race war Religious persecution · Gay bashing Blood libel · Black Legend Pedophobia · Ephebiphobia Movements Discriminatory Aryanism · Neo-Nazism · Ku Klux Klan National Party (South Africa) American Nazi Party Kahanism · Supremacism Anti... Female with red hair Male with red hair Red hair (also referred to as auburn, ginger, or titian) varies from a deep red through to bright copper. ... Vitamin D is a fat soluble vitamin that contributes to the maintenance of normal levels of calcium and phosphorus in the bloodstream. ... Albinism is a genetic condition resulting in a lack of pigmentation in the eyes, skin and hair. ... Griscelli syndrome is a rare autosomal childhood disorder characterised by hypopigmentation. ...

References

  1. ^ Hamilton AJ, Gomez BL. (2002). "Melanins in fungal pathogens". J. Med. Microbiol 53: 189. PMID 11871612. 
  2. ^ Dadachova E, Bryan RA, Huang X, Moadel1 T, Schweitzer1 AD, Aisen P, Nosanchuk JD, Casadevall A. (2007). "Ionizing radiation changes the electronic properties of melanin and enhances the growth of melanized fungi". PLoS ONE 2: e457. doi:10.1371/journal.pone.0000457. 
  3. ^ Anomalous Absorption of Sound in DBA Melanins. J. Applied Physics, 50(3): 1236-1244, 1979
  • Diana Clarke, "Melanin: Aging of the Skin and Skin Cancer," EzineArticles.com.
  • "Link 4-Melanin 95-97," taken from R.A.Nicolaus,G.Scherillo La Melanina.Un riesame su struttura,proprietà e sistemi, Atti della Accademia Pontaniana, Vol.XLIV,265-287, Napoli 1995.[16]
  • Dr. Mohammed O. Peracha, Dean Elloit, and Enrique Garcia-Valenzuela, "Occular Manifestations of Albinism" (Abstract at emedicine.com, Sept. 13, 2005).

  Results from FactBites:
 
Melanin definition - Medical Dictionary definitions of popular medical terms easily defined on MedTerms (258 words)
Dark-skinned people have more melanin than light- skinned people.
Melanin also acts as a sunscreen and protects the skin from ultraviolet light.
Freckles, which occur in people of all races, are small, concentrated areas of increased melanin production.
Melanin Properties - Afrocentrism and Pseudoscience (Skeptical Inquirer Spring 1992) (2104 words)
Melanin is not an alkaloid and there is no evidence whatsoever for melanin co-polymerizing with cocaine in vivo.
According to Welsing, the Dogon's melanin functions in a manner similar to an infrared telescope, and they were able to detect Sirius B through the melanin in their pineal glands.
The ability of melanin to absorb and respond to magnetic fields is a key component of his explanation of astrology.
  More results at FactBites »

 
 

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