Melanin

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Melanin (Greek μέλας, black; pronounced /ˈmɛlənɪn/ ( listen)) is a pigment that is ubiquitous in nature, being found in most organisms (spiders are one of the few animal groups in which it has not been detected). In animals melanin pigments are derivatives of the amino acid tyrosine. The most common form of biological melanin is eumelanin, a brown-black polymer of dihydroxyindole carboxylic acids, and their reduced forms. Technically all melanins are derivatives of polyacetylene. The most common melanin, dopamelanin is a mixed copolymer of polyacetylene, polyaniline and polypyrrole. Another common form of melanin is pheomelanin, a red-brown polymer of benzothiazine units largely responsible for red hair and freckles. The presence of melanin in the archaea and bacteria kingdoms is an issue of ongoing debate amongst researchers in the field. The increased production of melanin in human skin is called melanogenesis. Production of melanin is stimulated by DNA damage induced by UVB-radiation,[1] and it leads to a delayed development of a tan. This melanogenesis-based tan takes more time to develop, but it is long lasting.[2]

The photochemical properties of melanin make it an excellent photoprotectant. It absorbs harmful UV-radiation and transforms the energy into harmless heat through a process called "ultrafast internal conversion". This property enables melanin to dissipate more than 99.9% of the absorbed UV radiation as heat[3] (see photoprotection). This prevents the indirect DNA damage which is responsible for the formation of malignant melanoma and other skin cancers.

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