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Keratin (〔''OED'' 2nd edition, 1989 as .〕〔(Entry "keratin" ) in ''(Merriam-Webster Online Dictionary )''.〕) is a family of fibrous structural proteins. Keratin is the protein that protects epithelial cells from damage or stress that has potential to kill the cell. It is the key structural material making up the outer layer of human skin. It is the key structural component of hair and nails, and it provides the necessary strength and toughness for masticatory organs, such as the tongue and the hard palate. Keratin monomers assemble into bundles to form intermediate filaments, which are tough and form strong unmineralized tissues found in reptiles, birds, amphibians, and mammals. The only other biological matter known to approximate the toughness of keratinized tissue is chitin.〔(【引用サイトリンク】work=Webster's Online Dictionary )〕 ==Etymology== Keratin derives from Greek ''κερατίνη'' from Greek ''keras'' (''κέρας'') (genitive ''keratos'', ''κέρατος'') meaning "horn" originating from the Proto-Indo-European '' *''ḱer''-'' of the same meaning.〔(【引用サイトリンク】work=Online Etymology Dictionary ) (【引用サイトリンク】work=Online Etymology Dictionary )〕 Its Greek root is composed of "horn like", i.e., ''kerato'' (Greek ''κέρατο'')〔(【引用サイトリンク】work=Online Etymology Dictionary ) (【引用サイトリンク】work=Online Etymology Dictionary )〕 to which the chemical suffix ''-in'' is appended.〔(【引用サイトリンク】work=Online Etymology Dictionary )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Keratin」の詳細全文を読む スポンサード リンク
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