Keratin

keratinizationkeratinouskeratinizedcornificationcornifiedKeratinshornhornykeratinisednonkeratinized
Keratin is one of a family of fibrous structural proteins.wikipedia
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Horn (anatomy)

hornhornshorned
It is the key structural material making up hair, nails, feathers, horns, claws, hooves, calluses, and the outer layer of skin among vertebrates.
A horn - a permanent pointed projection on the head of various animals - consists of a covering of keratin and other proteins surrounding a core of live bone.

Hair

glabrousglabrescenthuman hair
It is the key structural material making up hair, nails, feathers, horns, claws, hooves, calluses, and the outer layer of skin among vertebrates.
All mammalian hair is composed of keratin, so the make-up of hair follicles is not the source of varying hair patterns.

Feather

feathersplumagebarbule
It is the key structural material making up hair, nails, feathers, horns, claws, hooves, calluses, and the outer layer of skin among vertebrates.
Feathers are among the most complex integumentary appendages found in vertebrates and are formed in tiny follicles in the epidermis, or outer skin layer, that produce keratin proteins.

Hoof

hooveshoovehooved
It is the key structural material making up hair, nails, feathers, horns, claws, hooves, calluses, and the outer layer of skin among vertebrates.
A hoof ( or ), plural hooves ( or ) or hoofs, is the tip of a toe of an ungulate mammal, strengthened by a thick, and horny keratin covering.

Claw

talonsclawstalon
It is the key structural material making up hair, nails, feathers, horns, claws, hooves, calluses, and the outer layer of skin among vertebrates.
A true claw is made of hard protein called keratin.

Scleroprotein

fibrous proteinfibrousfibrous proteins
Keratin is one of a family of fibrous structural proteins.
There are many scleroprotein superfamilies including keratin, collagen, elastin, and fibroin.

Skin

cutaneousskin cellanimal skin
It is the key structural material making up hair, nails, feathers, horns, claws, hooves, calluses, and the outer layer of skin among vertebrates.
Reptiles and fish have hard protective scales on their skin for protection, and birds have hard feathers, all made of tough β-keratins.

Alpha-keratin

α-keratinalphaalpha-keratins
Alpha-keratin, or α-keratin, is a type of keratin found in vertebrates.

Baleen

whalebonewhale bonebone
Additionally, the baleen plates of filter-feeding whales are made of keratin.
Baleen is similar to bristles and consists of keratin, the same substance found in human fingernails and hair.

Keratinocyte

keratinocytesskin cellsdead skin cells
Keratin filaments are abundant in keratinocytes in the cornified layer of the epidermis; these are proteins which have undergone keratinization.
A number of structural proteins (filaggrin, keratin), enzymes (proteases), lipids, and antimicrobial peptides (defensins) contribute to maintain the important barrier function of the skin.

Chitin

chitinouschitinous polymer matrixchitohexaose
The only other biological matter known to approximate the toughness of keratinized tissue is chitin.
In terms of function, it may be compared to the protein keratin.

Stratum corneum

horny layercornified layerepidermal permeability barrier
Their cytoplasm shows filamentous keratin.

Amphibian

Amphibiaamphibiansamphibious
Keratin monomers assemble into bundles to form intermediate filaments, which are tough and form strong unmineralized epidermal appendages found in reptiles, birds, amphibians, and mammals.
Their skin contains little keratin and lacks scales, apart from a few fish-like scales in certain caecilians.

Epidermis

epidermalepidermal cellsepidermal layer
Keratin filaments are abundant in keratinocytes in the cornified layer of the epidermis; these are proteins which have undergone keratinization.
The cells in the stratum granulosum do not divide, but instead form skin cells called keratinocytes from the granules of keratin.

Intermediate filament

intermediate filamentsdesmosome-keratinfilament
Keratin monomers assemble into bundles to form intermediate filaments, which are tough and form strong unmineralized epidermal appendages found in reptiles, birds, amphibians, and mammals.
The structure of proteins that form IF was first predicted by computerized analysis of the amino acid sequence of a human epidermal keratin derived from cloned cDNAs.

Whale

whalesflukeflukes
Additionally, the baleen plates of filter-feeding whales are made of keratin.
Cetaceans are divided into two parvorders: the largest parvorder, Mysticeti (baleen whales), is characterized by the presence of baleen, a sieve-like structure in the upper jaw made of keratin, which it uses to filter plankton, among others, from the water; Odontocetes (toothed whales) are characterized by bearing sharp teeth for hunting, as opposed to their counterparts' baleen.

Beak

billcereculmen
The outer surface of the beak consists of a thin horny sheath of keratin called the rhamphotheca, which can be subdivided into the rhinotheca of the upper mandible and the gnathotheca of the lower mandible.

Turtle

turtlesTestudinesTestudines indet.
Scutes are made up of the fibrous protein keratin that also makes up the scales of other reptiles.

Beta-keratin

β-keratinβ-keratinsbeta keratin
Because the accurate use of the term keratin is limited to the alpha-keratins, the term "beta-keratins" in recent works is replaced by "corneous beta-proteins" or "keratin-associated beta-proteins."

Scale (anatomy)

scalesscalescaly
The upper surface is keratin.

KRT83

K83type II hair keratin 3
The keratins include the following proteins of which KRT23, KRT24, KRT25, KRT26, KRT27, KRT28, KRT31, KRT32, KRT33A, KRT33B, KRT34, KRT35, KRT36, KRT37, KRT38, KRT39, KRT40, KRT71, KRT72, KRT73, KRT74, KRT75, KRT76, KRT77, KRT78, KRT79, KRT8, KRT80, KRT81, KRT82, KRT83, KRT84, KRT85 and KRT86 have been used to describe keratins past 20.
The protein encoded by this gene is a member of the keratin gene family.

Nail (anatomy)

nailnailsfingernail
It is the key structural material making up hair, nails, feathers, horns, claws, hooves, calluses, and the outer layer of skin among vertebrates.
A nail is a horn-like keratinous envelope covering the tips of the fingers and toes in most primates.

KRT73

K73
The keratins include the following proteins of which KRT23, KRT24, KRT25, KRT26, KRT27, KRT28, KRT31, KRT32, KRT33A, KRT33B, KRT34, KRT35, KRT36, KRT37, KRT38, KRT39, KRT40, KRT71, KRT72, KRT73, KRT74, KRT75, KRT76, KRT77, KRT78, KRT79, KRT8, KRT80, KRT81, KRT82, KRT83, KRT84, KRT85 and KRT86 have been used to describe keratins past 20.
KRT73 is a keratin gene.

KRT23

K23
The keratins include the following proteins of which KRT23, KRT24, KRT25, KRT26, KRT27, KRT28, KRT31, KRT32, KRT33A, KRT33B, KRT34, KRT35, KRT36, KRT37, KRT38, KRT39, KRT40, KRT71, KRT72, KRT73, KRT74, KRT75, KRT76, KRT77, KRT78, KRT79, KRT8, KRT80, KRT81, KRT82, KRT83, KRT84, KRT85 and KRT86 have been used to describe keratins past 20.
The protein encoded by this gene is a member of the keratin family.

Sulfur

sulphurSbrimstone
In addition to intra- and intermolecular hydrogen bonds, the distinguishing feature of keratins is the presence of large amounts of the sulfur-containing amino acid cysteine, required for the disulfide bridges that confer additional strength and rigidity by permanent, thermally stable crosslinking —in much the same way that non-protein sulfur bridges stabilize vulcanized rubber.
Disulfides, S–S bonds, confer mechanical strength and insolubility of the protein keratin, found in outer skin, hair, and feathers.