Keratin, in hair

There are 20 amino acids found in the human body that are involved in protein synthesis. Refer to your textbook for a table of the 20 amino acids. The sequence of the amino acids dictates the properties of a protein. Examples of proteins include keratin in hair, hemoglobin, insulin, antibodies, and enzymes. 

Permanent hair colors can be achieved with tint shampoos. The shampoo base is adjusted to an alkaline pH and contains oxidation dye intermediates. Before application, it is mixed with hydrogen peroxide or a hydrogen peroxide addition compound. In comparison with oxidation hair dyes, tint shampoos employ lower concentrations of base and oxidant. This suppresses the simultaneous bleaching process that occurs during dyeing (see Section 5.4.2). As a result, damage to the keratin in hair is diminished, but the uniform coloring action is lost. 

Arado, M. G., Garrote, I. V., Laborde, L., Bosch, A., and Ferrari, L. A. (2001). Cocaine and Lidocaine in hair and nails from decomposed bodies, in Proceedings of the 2001 Annual Meeting of The International Association of Forensic Toxicologists— Poster Abstracts Vol. 2002. http //www.tiaft.org/tiaft2001/posters/p75.doc. Baden, H. P. (1990). Hair keratin, in Hair and Hair Diseases (C. E. Orfanos and R. 

Baden, H. P., Hair keratin, in Hair and Hair Diseases, Orfanos, C. E. and Happle, R., Eds., Springer-Verlag, Berlin, 1989, 45. 

Both the myosin in muscle and a-keratin in hair are proteins composed almost entirely of a-helices. 

Figure 3.34. An a -Helical Coiled Coil. The two helices wind around one another to form a superhelix. Such structures are found in many proteins including keratin in hair, quills, claws, and horns.

Different proteins have different physical properties. Some—such as casein in milk, ovalbumin in egg whites, and hemoglobin in blood—are water-soluble. Others—such as keratin in hair, fibroin in spider silk, and collagen in connective tissue—are flexible solids. 

Structural proteins such as collagen in connective tissue and keratin in hair and nails. 

Keratins - ot-Keratins are the major proteins of hair and fingernails and a compose a major fraction of animal skin, oi-keratins are classified in the broad group of intermediate filament proteins, which play important structural roles in nuclei, cytoplasm, and cell surfaces. Their secondary structure is composed predominantly of -helices. Figure 6.11 shows the coiled-coil structure of the ot-keratin in hair. The chemical composition of the cysteine residues in ot-keratin affects its macromolecular structure and function. For example, hair has relatively few cysteine cross-links, whereas fingernails have many such cross-links, / -keratins, on the other hand, contain much more pleated sheet secondary strucure than ot-keratins and are found in feathers and scales. 

As you might imagine, a molecule as large as a protein has a great deal of flexibility and can assume a variety of overall shapes. The specific shape that a protein assumes depends on its function. For long, thin structures, such as hair, wool and silk fibers, and tendons, an elongated shape is required. This may involve an a-helical secondary structure, as found in the protein a-keratin in hair and wool or in the collagen found in tendons [Fig. 21.23(a)], or it may... 

Thus muscle, collagen (in bone), keratin (in hair, nails and beaks) and albumin are all copolymers of very similar amino acids but have quite different physical properties. In deoxyribonucleic acid (DN A), the genetic template, the sequence of monomers is precise and variations are the cause of genetic mutations. Although the polypeptides are of ultimate importance in life processes they are not important in the context of materials and will not be considered further in this book. However, they have had a significant impact on modern polymer science since the synthesis of the first man-made polyamide fibre. Nylon, by Carothers was modelled on the structure of a silk, a naturally occurring polypeptide. 

This proeess involves the denaturation and renaturation of keratins. Although disulfide bonds are formed at different positions in the renatured proteins, there is no biological consequence because keratins in hair do not have any specific functions. The word permanent applies only to the portion of hair treated with the reducing and oxidizing agents, and the wave lasts until new and untreated keratins replace it. 

A second form of keratin, known as fi-keratin, is produced by stretching the a-keratin in hair to about twice its original length. The X-ray diffraction pattern of -keratin is similar to that of silk fibroin (page 56) and its structure, like that of fibroin, is based on the /5-pleated sheet. There is a difference, however, in that polypeptide chains are in a parallel (Figure 5.2a) and not an antiparallel arrangement. 

The more flexible and elastic keratins in hair have fewer inter-chain disulfide bridges than the keratins in mammalian fingernails, hooves and claws (homologous structures). 

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