Keratin

Keratin (/ˈkɛrətɪn/^[1]^[2]) is one of a family of structural fibrous proteins also known as scleroproteins. It is the key structural material making up scales, hair, nails, feathers, horns, claws, hooves, and the outer layer of skin in vertebrates. Keratin also protects epithelial cells from damage or stress. Keratin is extremely insoluble in water and organic solvents. 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.^[3]^[4] Excessive keratinization participate in fortification of certain tissues such as in horns of cattle and rhinos, and armadillos' osteoderm.^[5] The only other biological matter known to approximate the toughness of keratinized tissue is chitin.^[6]^[7]^[8] Keratin comes in two types: the primitive, softer forms found in all vertebrates and the harder, derived forms found only among sauropsids (reptiles and birds).

Spider silk is classified as keratin,^[9] although production of the protein may have evolved independently of the process in vertebrates.

^ OED 2nd edition, 1989 as /ˈkɛrətɪn/
^ Entry "keratin" Archived 2013-05-09 at the Wayback Machine in Merriam-Webster Online Dictionary Archived 2017-09-22 at the Wayback Machine.
^ Fraser R (1972). Keratins: Their composition, structure and biosynthesis. Bannerstone House: Charles C Thomas. pp. 3–6. ISBN 978-0-398-02283-9.
^ Wang B, Yang W, McKittrick J, Meyers MA (March 2016). "Keratin: Structure, mechanical properties, occurrence in biological organisms, and efforts at bioinspiration". Progress in Materials Science. 76: 229–318. doi:10.1016/j.pmatsci.2015.06.001.
^ Nasoori A (2020). "Formation, structure, and function of extra-skeletal bones in mammals". Biological Reviews of the Cambridge Philosophical Society. 95 (4): 986–1019. doi:10.1111/brv.12597. PMID 32338826.
^ "Keratin". Webster's Online Dictionary. 22 May 2023. Archived from the original on 1 May 2021. Retrieved 9 August 2018.
^ Vincent JF, Wegst UG (July 2004). "Design and mechanical properties of insect cuticle". Arthropod Structure & Development. 33 (3): 187–199. Bibcode:2004ArtSD..33..187V. doi:10.1016/j.asd.2004.05.006. PMID 18089034.
^ Tombolato L, Novitskaya EE, Chen PY, Sheppard FA, McKittrick J (February 2010). "Microstructure, elastic properties and deformation mechanisms of horn keratin". Acta Biomaterialia. 6 (2): 319–330. doi:10.1016/j.actbio.2009.06.033. PMID 19577667.
^ "Keratin". VEDANTU. Retrieved 2022-01-07.^{[permanent dead link]}

[1] OED 2nd edition, 1989 as /ˈkɛrətɪn/

[2] Entry "keratin" Archived 2013-05-09 at the Wayback Machine in Merriam-Webster Online Dictionary Archived 2017-09-22 at the Wayback Machine.

[3] Fraser R (1972). Keratins: Their composition, structure and biosynthesis. Bannerstone House: Charles C Thomas. pp. 3–6. ISBN 978-0-398-02283-9.

[Wang_2016-4] Wang B, Yang W, McKittrick J, Meyers MA (March 2016). "Keratin: Structure, mechanical properties, occurrence in biological organisms, and efforts at bioinspiration". Progress in Materials Science. 76: 229–318. doi:10.1016/j.pmatsci.2015.06.001.

[5] Nasoori A (2020). "Formation, structure, and function of extra-skeletal bones in mammals". Biological Reviews of the Cambridge Philosophical Society. 95 (4): 986–1019. doi:10.1111/brv.12597. PMID 32338826.

[6] "Keratin". Webster's Online Dictionary. 22 May 2023. Archived from the original on 1 May 2021. Retrieved 9 August 2018.

[7] Vincent JF, Wegst UG (July 2004). "Design and mechanical properties of insect cuticle". Arthropod Structure & Development. 33 (3): 187–199. Bibcode:2004ArtSD..33..187V. doi:10.1016/j.asd.2004.05.006. PMID 18089034.

[8] Tombolato L, Novitskaya EE, Chen PY, Sheppard FA, McKittrick J (February 2010). "Microstructure, elastic properties and deformation mechanisms of horn keratin". Acta Biomaterialia. 6 (2): 319–330. doi:10.1016/j.actbio.2009.06.033. PMID 19577667.

[9] "Keratin". VEDANTU. Retrieved 2022-01-07.^{[permanent dead link]}

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