Proteins a-keratin

Pauling s audacious scientific career included the use of first principles and molecular models to intuit the structure of the protein a-keratin. He also was the first to characterize the basis for a disease at the molecular level—sickle-cell anemia—the result of a substitution of one amino acid for another in hemoglobin. 

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... 

Figure 9.4 Animal hair and spiderwebs are constructed of the fibrous proteins a-keratin and P-keratin, respectively. What properties of fibrous proteins make hair, fur, and spiderwebs useful ...

In the proteins a-keratin (found in hair), myosin (found in muscle), epidermin (found in skin), and fibrin (found in blood clots), two or more helices interact (supracoiling) to form a cable (see I Figure 9.7). These cables make up bundles of fibers that lend strength to the tissue in which they are found. 

Wool belongs to a family of proteins, the keratins, that also includes hair and other types of animal protective tissues such as horn, nails, feathers, and the outer skin layers. The relative importance of wool as a textile fiber has declined over the decades as synthetic fibers have increa singly been used in textile consumption. Wool is still an important fiber in the middle and upper price ranges of the textile market. It is also an extremely important export for several nations, notably AustraUa, New Zealand, South Africa, and Argentina and commands a price premium over most other fibers because of its outstanding natural properties of soft handle (the feel of the fabric), moisture absorption abiUties (and hence comfort), and superior drape (the way the fabric hangs) (see Fibers Textiles). Table 2 shows wool production and sheep numbers in the world s principal wool-producing countries. 

Wool, as a keratin, is a highly cross-linked, insoluble proteinaceous fiber, and few animals have developed the specialized digestive systems that aUow them to derive nutrition from the potential protein resource. In nature, these few keratin-digesting animals, principally the larvae of clothes moths and carpet beetles, perform a useful function in scavenging the keratinous parts of dead animals and animal debris (fur, skin, beak, claw, feathers) that ate inaccessible to other animals. It is only when these keratin-digesting animals attack processed wool goods that they are classified as pests. Very often they enter domestic or industrial huildings from natural habitats such as birds nests. 

The central rod domain of a keratin protein is approximately 312 residues in length. What is the length (in A) of the keratin rod domain If this same peptide segment were a true u-helix, how long would it be If the same segment were a /3-sheet, what would its length be ... 

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. 

The secondary structure is responsible for some of the physical properties of proteins. For example, structural proteins such as a-keratins in skin and hair are fibrous in nature, and have good elastic... 

The separation of cystine and tyrosine as they are obtained by hydrolysis with hydrochloric acid was described by Morner in I901. The protein—hair, keratin from horn, eggshells, etc.—was boiled with five times its quantity of 13 per cent hydrochloric acid under a reflux condenser on a water bath for six to seven days. The solution was then decolorised with charcoal and evaporated in vacuo, and the residue dissolved in 60 to 70 per cent, alcohol. The two acids then crystallised out on neutralising with soda, and were separated by fractional crystallisation from ammonia if much tyrosine was present it separated out first, but if cystine exceeded tyrosine in quantity this compound crystallised out first the remainder was only separated with difficulty. Embden separated the mixture of the two acids by means of very dilute nitric acid, in which tyrosine is very easily soluble, but cystine with difficulty. Their separation may also be effected by precipitation with mercuric sulphate in 5 per cent, sulphuric acid solution in which the mercury compound of tyrosine is soluble (Hopkins and Cole). 

FIGURE 3-1 Some functions of proteins, (a) The light produced by fireflies is the result of a reaction involving the protein luciferin and ATP, catalyzed by the enzyme luciferase (see Box 13-2). (b) Erythrocytes contain large amounts of the oxygen-transporting protein hemoglobin. (c) The protein keratin, formed by all vertebrates, is the chief structural component of hair, scales, horn, wool, nails, and feath-... 

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