Keratin
From the Simple English Wikipedia, the free encyclopedia that anyone can change
Keratins are a family of fibrous structural proteins. They are tough and insoluble, they form the hard but nonmineralized structures that one can find in reptiles, birds, amphibians and mammals. A similar biological toughness one can find only by chitin.
There are various types of keratins, even within a single animal.
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[change] Variety of animal uses
Keratins are the main constituent of structures that grow from the skin:
- the α-keratins in the hair (including wool), horns, nails, claws and hooves of mammals
- the harder β-keratins in the scales and claws of reptiles, their shells (chelonians, such as tortoise, turtle, terrapin), and in the feathers, beaks, and claws of birds. (These keratins are formed primarily in beta sheets. However, beta sheets are also found in α-keratins.)[1]
Arthropods such as crustaceans often have parts of their armor or exoskeleton made of keratin, sometimes in combination with chitin.
Keratins are also found in the gastrointestinal tracts of many animals, including roundworms (who also have an outer layer made of keratin).
Although it is now difficult to be certain, the scales, claws, some protective armour and the beaks of dinosaurs would, almost certainly, have been composed of a type of keratin.
[change] Silk
The silk fibroins produced by insects and spiders are often classified as keratins, though it is unclear whether they are phylogenetically related to vertebrate keratins.
Silk found in insect pupae, and in spider webs and egg casings, also has twisted β-pleated sheets incorporated into fibers wound into larger supermolecular aggregates.
[change] References
- ↑ Kreplak L, Doucet J, Dumas P, Briki F (2004). "New aspects of the alpha-helix to beta-sheet transition in stretched hard alpha-keratin fibers". Biophys J 87 (1): 640-7. PMID 15240497.
