Hair is composed largely of fibers of the protein keratin. Individual keratin fibers are covalently crosslinked to one another by many disulfide (S–S) bonds. If curly hair is treated with mild reducing agents that break a few of the cross-links, pulled straight, and then oxidized again, it remains straight. Draw a diagram that illustrates the three different stages of this chemical and mechanical process at the level of the keratin filaments, focusing on the disulfide bonds. What do you think would happen if hair were treated with strong reducing agents that break all the disulfide bonds?

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(A) (B) noncovalent bonds ligand protein