keratin (kĕr`ətĭn), any one of a class of fibrous protein protein, any of the group of highly complex organic compounds found in all living cells and comprising the most abundant class of all biological molecules. Protein comprises approximately 50% of cellular dry weight.
..... Click the link for more information. molecules that serve as structural units for various living tissues. The keratins are the major protein components of hair, wool, nails, horn, hoofs, and the quills of feathers. These proteins generally contain large quantities of the sulfur-containing amino acids amino acid (əmē`nō)
..... Click the link for more information. , particulary cysteine cysteine (sĭs`tēn), organic compound, one of the 20 amino acids commonly found in animal proteins .
..... Click the link for more information. . The helical keratin molecules twist around each other to form elongated strands called intermediate filaments. The formation of a covalent chemical bond chemical bond, mechanism whereby atoms combine to form molecules . There is a chemical bond between two atoms or groups of atoms when the forces acting between them are strong enough to lead to the formation of an aggregate with sufficient stability to be regarded as
..... Click the link for more information. called a disulfide bridge between the sulfer atoms on two cysteins on separate polypeptide chains of keratin allows for the cross-linkage of these chains and results in a fairly rigid aggregate. This phenomenon is seen to be consistent with the physiological role of the keratins, which provide a tough, fibrous matrix for the tissues in which they are found. Human hair is approximately 14% cystine (cysteins cross-linked by disulfide bridges).

keratin

Fibrous structural protein of hair, nails, hooves, wool, feathers, and skin. A quarter of the amino acids in keratin are cystine, whose ability to form strong bridging (disulfide) bonds with other cystine units accounts for keratin's great stability. Keratin does not dissolve in cold or hot water and does not easily undergo proteolysis. Its fibres are 10–12% longer at maximum water content (about 16%) than when dry. The sulfurous smell of burning keratin is distinctive.

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keratin

keratin