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Encyclopedia > Melanosome

In a biological cell, a melanosome is an organelle containing melanin, the most common light-absorbing pigment found in the animal kingdom. Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell being used to describe the smallest unit of a living organism Cells in culture, stained for keratin (red) and DNA (green) The cell is the... Schematic of typical animal cell, showing subcellular components. ... Broadly, melanin is any of the polyacetylene, polyaniline, and polypyrrole blacks and browns or their mixed copolymers. ...


Cells which produce melanosomes are called melanocytes, whereas cells which have merely engulfed the melanosomes are called melanophages. This article or section does not cite its references or sources. ...

Contents

Shape

Melanosomes are bound by a lipid membrane and are generally rounded, sausage-like or cigar-like in shape.


The shape is constant for a given species and cell type.


They have a characteristic ultrastructure on electron microscopy, which varies according to the maturity of the melanosome, and for research purposes a numeric staging system is sometimes used. Ultrastructure is the detailed structure of a biological specimen, such as a cell, tissue, or organ, that can be by electron microscopy. ... The electron microscope is a microscope that can magnify very small details with high resolving power due to the use of electrons rather than light to scatter off material, magnifying at levels up to 500,000 times. ...


Synthesis of melanin

They are dependent for their pigment on a set of enzymes within the cell (especially tyrosinase) which synthesise the large polymers generically known as melanin. Tyrosinase (monophenol monooxygenase) (EC 1. ... Broadly, melanin is any of the polyacetylene, polyaniline, and polypyrrole blacks and browns or their mixed copolymers. ...


Before it contains much pigment (sufficient to be seen on light microscopy), it is known as a pre-melanosome. Microscopy is any technique for producing visible images of structures or details too small to otherwise be seen by the human eye. ...


Dysfunction or absence of the melanin-synthesising enzymes leads to various patterns of albinism. 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). ...


Pseudopodia

In some melanocytes, the melanosomes remain static within the cell. In other types of melanocyte, the cell can extend its surface as long pseudopodia, carrying melanosomes away from the centre of the cell and increasing the cell's effectiveness in absorbing light. Pseudopods or pseudopodia (false feet) are temporary projections of eukaryotic cells. ...


For example, this happens slowly in dermal melanocytes in responsive to ultraviolet light, as well as production of new melanosomes and increased 'donation' of melanosomes to adjacent keratinocytes, the normal skin surface cells. Note: Ultraviolet is also the name of a 1998 UK television miniseries about vampires. ... The keratinocyte is the major cell type of the epidermis, making up about 90% of epidermal cells. ...


Collectively these changes are responsible for 'tanning' after exposure to UV or sunlight.


In animals

In many species of fish, amphibians, crustaceans and reptiles, melanosomes can be highly mobile within the cell in response to hormonal (or sometimes neural) control, and this leads to visible changes in colour that are used for behavioural signalling. For other uses, see Fish (disambiguation). ... For other uses, see Amphibian (disambiguation). ... Classes Remipedia Cephalocarida Branchiopoda Ostracoda Maxillopoda Malacostraca The crustaceans (Crustacea) are a large group of arthropods (55,000 species), usually treated as a subphylum. ... Orders  Crocodilia - Crocodilians scary crocodiles. ...


The beautiful and rapid colour changes seen in many cephalopods (octopuses and squid) are based, however, on a different system, the chromatophore organ. Orders Subclass Nautiloidea †Plectronocerida †Ellesmerocerida †Actinocerida †Pseudorthocerida †Endocerida †Tarphycerida †Oncocerida †Discosorida Nautilida †Orthocerida †Ascocerida †Bactritida Subclass †Ammonoidea †Goniatitida †Ceratitida †Ammonitida Subclass Coleoidea †Belemnoidea †Aulacocerida †Belemnitida †Hematitida †Phragmoteuthida Neocoleoidea (most living cephalopods) ?†Boletzkyida Sepiida Sepiolida Spirulida Teuthida Octopoda Vampyromorphida The cephalopods (Greek plural (kephalópoda); head-foot) are the mollusk class... Zebrafish chromatophores mediate background adaptation on exposure to dark (top) and light environments (bottom). ...


Templating

Melanosomes are believed to template melanin polymerization by way of amyloidogenesis of the protein pMel, which is present in abundant quantities in melanosomes. For other uses, see Amyloid (disambiguation). ...


References

  • Fowler, et al. PLoS Biol. 2005 Nov 29;4(1)

External links


  Results from FactBites:
 
Melanosome - Wikipedia, the free encyclopedia (344 words)
A melanosome is a cellular organelle containing melanin, the commonest light-absorbing pigment found in the animal kingdom.
Melanosomes are bound by a lipid membrane and are generally rounded, sausage-like or cigar-like in shape.
Melanosomes are believed to template melanin polymerization by way of amyloidogenesis of the protein pMel, which is present in abundant quantities in melanosomes.
Albinism and Melanosomal Abnormalities (6401 words)
An albino locus-induced diminution of melanosome size suggests that the albino locus is involved in structural features of melanosomes not directly related to the synthesis and deployment of tyrosinase.
Ratio data on melanosome length-to-width confirm that the agouti locus determines melanosome shape, either spherical or elliptical; melanization is not required for melanosomes to achieve their agouti-locus-determined shapes.
On the ultrastructural level, the hypomelanotic skin and hair of TS were associated with a decrease in the synthesis, melanization, and size of melanosomes; the decrease in the size of melanosomes resulted in the aggregation of melanosomes (i.e., a melanosome complex) in the keratinocytes in all the specimens examined.
  More results at FactBites »

 
 

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