10 g out to dinner that night. e She was anxious to see her friends, as they wer
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10 g out to dinner that night. e She was anxious to see her friends, as they were all Case Background Hair is composed basically of wrapped layers of keratinized cells; the keratin protein of the hair cells is comprised of a great deal of sulfur-containing amino acids. By chemically manipulating the sulfur-to- sulfur (disulfide) chemical bonds of thes amino acids, the three-dimensional structure of hair can be altered. Hair can be permed into various three-dimensional structures by manipulation of disulfide bonds such as are found in keratin. The amino acid cysteine contains a free sulfhydryl (-S-H) side group (Figure 1.1) Keratin protein contains about 28% cysteine and thus has a great deal of sulfhydryl side units available for chemical manipulation by hairdressers Consider a protein molecule with two cysteine residues of the protein brought into close proximity (Figure 1.2). Such a situation could occur during a perm. When hair curlers can physically bring new cysteine amino acids into close proximity on the same protein chain, a covalent bond termed a disulfide bond can be formed and a loop in the protein can result (Figure During a perm, the disulfide bonds are first reduced (broken by using a chemical that will add hydrogen to the disulfide bonds (Figure 1.5). Disulfide bonds will be broken creating free sulfhydryl groups (-S-H). The three dimensional structure of the hair's keratin protein will then be amenable to structural manipulation by the hairdresser. The hair proteins can be put into new shapes with curlers and the disulfide bonds can be reformed to hold the proteins in the new three dimensional shapes. To create new disulfide bonds, a strong base is often used to remove the hydrogen atoms from the free sulfhydryl groups. New disulfide bonds then form if hydrogens that occurs is an oxidation reaction (Figure 1.3). Oxidation is a term in chemistry to denote the loss of hydrogen during a chemical reaction. The 2 cysteine amino acids, after formation of the (H+) are removed from adjacent sulfhydryl groups of 2 cysteiner disulfide bond, are collectively termed cystine.Explanation / Answer
Keratin is a type of structural protein found in hairs, nails, hoofs and feathers.Keratin is a protein formed by the combination of 18 amino acids among which cysteine is in high quantity. Cysteineis rich in sulphur(-S-H) and plays an important role in the cohesion of the hair. Within the body of the hair which is cortex keratin is in protofibrils form which is contains 4 chains of keratin. These chains can be held together by small force like hydrogen bonding and stronger force like disulphide linkage (-S-S-).By acting on these bond the shape of the hair can be changed.On microscopic level in curly hairs the keratin is present in form of alpha keratin which forms a helical structure. These helical structure then integrate in a left hand coiled structure. The more interaction it have the more tightly it coiled.
A hair dresser use first waving lotion which contains ammonium thioglycolate on curly hairs which changes the (-S-S-) bond into (-S-H) which processes is known as reduction(reduction is addition of hydrogen or removal of oxygen) It frees the disulphide linkage and makes the hair straight. The hair can be curl again with curler like H2O2 which oxidises some of the adjacent thiol groups to disulfide links to fix the new orientation of the hair strands.This reforming of disulphide bond is oxidation. Oxidation is a process of removal of hydrogen or addition of oxygen.This is how the whole mechanism works
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