melanin


melanin
melaninlike, adj.
/mel"euh nin/, n.
any of a class of insoluble pigments, found in all forms of animal life, that account for the dark color of skin, hair, fur, scales, feathers, etc.
[1835-45; MELAN- + -IN2]

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Any of several organic compounds, dark biological pigments that give coloration (shades of yellow to brown) to skin, hair, feathers, scales, eyes, and some internal tissues, notably the substantia nigra in the brain.

In humans, melanins help protect the skin against the damaging effects of ultraviolet radiation, but melanoma may arise from cells that produce it. The amount in the skin depends on both genetic and environmental factors. Melanin is produced from the amino acid tyrosine; albinos lack the enzyme that catalyzes that reaction (see albinism).

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▪ biological pigment
      a dark biological pigment (biochrome) found in skin, hair, feathers, scales, eyes, and some internal membranes; it is also found in the peritoneum of many animals (e.g., frogs), but its role there is not understood. Formed as an end product during metabolism of the amino acid tyrosine, melanins are conspicuous in dark skin moles of humans; in the black dermal melanocytes (pigment cells) of most dark-skinned peoples; and as brown, diffuse spots in the epidermis.

      Melanism refers to the deposition of melanin in the tissues of living animals. The chemistry of the process depends on the metabolism of the amino acid tyrosine, the absence of which results in albinism, or lack of pigmentation. Melanism can also occur pathologically, as in a malignant melanoma, a cancerous tumour composed of melanin-pigmented cells.

      Melanic pigmentation is advantageous in many ways: (1) It is a barrier against the effects of the ultraviolet rays of sunlight. On exposure to sunlight, for example, the human epidermis undergoes gradual tanning as a result of an increase in melanin pigment. (2) It is a mechanism for the absorption of heat from sunlight, a function that is especially important for cold-blooded animals. (3) It affords concealment to certain animals that become active in twilight. (4) It limits the incidence of beams of light entering the eye and absorbs scattered light within the eyeball, allowing greater visual acuity. (5) It provides resistance to abrasion because of the molecular structure of the pigment. Many desert-dwelling birds, for example, have black plumage as an adaptation to their abrasive habitat.

      “Industrial” melanism has occurred in certain moth populations, in which the predominant coloration has changed pale gray to dark-coloured individuals. This is a striking example of rapid evolutionary change; it has taken place in less than 100 years. It occurs in moth species that depend for their survival by day on blending into specialized backgrounds, such as lichened tree trunks and boughs. Industrial pollution, in the form of soot, kills lichens and blackens the trees and ground, thus destroying the protective backgrounds of light-coloured moths, which are rapidly picked off and eaten by birds. Melanic moths, by their camouflage, then become selectively favoured. “Industrial” melanic moths have arisen from recurrent mutations and have spread via natural selection. See coloration; integument.

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Universalium. 2010.

Look at other dictionaries:

  • Melanin — Mel a*nin, n. [Gr. me las, me lanos, black.] (Physiol.) A black pigment found in the pigment bearing cells of the skin (particularly in the skin of the negro), in the epithelial cells of the external layer of the retina (then called {fuscin}), in …   The Collaborative International Dictionary of English

  • melanin — melanin. См. меланин. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • Melanin — Melanin, das schwarze Pigment, welches sich als Überzug auf der Choroïdea des Auges findet. Ob das Pigment in den schwarzen Bronchialdrüsen, dem Rete Malpighii der Neger, in der Melanose (s.d.) u. dem schwarzen Serum des Lungengewebes mit diesem… …   Pierer's Universal-Lexikon

  • Melanīn — Melanīn, schwarzer Farbstoff in der Netzhaut des Auges (Augenschwarz), in der Haut des Negers, in den Pigmentierungen der Lungen und Bronchialdrüsen Erwachsener, im Bauchfell vieler Fische, bei Amphibien, in der Tinte der Sepien, in den… …   Meyers Großes Konversations-Lexikon

  • Melanin — Melanīn, Ophthalmomelanin, Augenschwarz, ein schwarzer Farbstoff in der Gefäßhaut des Auges, der Haut des Negers, der Tinte der Sepien und krankhaften Geschwülsten, eisenreich …   Kleines Konversations-Lexikon

  • Melanin — Melanin, braunes oder schwarzes höher molekulares Pigment; bei vielen Tiergruppen vorhanden; aus der Aminosäure Tyrosin gebildet; kommt bei Wirbeltieren in den Melanocyten der Haut vor und schützt Oberhaut und Augen vor zu starker UV Strahlung.… …   Deutsch wörterbuch der biologie

  • melanin — dark brown or black pigment found in animal bodies, 1832, Modern Latin, with chemical suffix IN (Cf. in) (2); first element from Gk. melas (gen. melanos) black, from PIE root *mel dark, soiled, dirty (Cf. Skt. malinah dirty, stained, black, Lith …   Etymology dictionary

  • melanin — melànīn m <G melanína> DEFINICIJA fiziol. tamnosmeđi do crni pigment u čovjeka i životinja; daje boju koži, kosi i očima, štiti od štetnog djelovanja Sunčevih zraka ETIMOLOGIJA grč. mélas: crn + in …   Hrvatski jezični portal

  • melanin — ► NOUN ▪ a dark pigment in the hair and skin, responsible for tanning of skin exposed to sunlight. ORIGIN from Greek melas black …   English terms dictionary

  • melanin — [mel′ə nin] n. [ MELAN(O) + IN1] a brownish black pigment found in skin, hair, and other animal or plant tissues …   English World dictionary

  • Melanin — Not to be confused with melamine, melatonin, or Melanotan (disambiguation). Melanin pigment (dark granular material center of image) in a pigmented melanoma. Pap stain. Melanin …   Wikipedia


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