The principal component of hair is a protein molecule called keratin. All protein molecules consist of long chains of small molecular units, the amino acids, of which there are 20 different kinds. Each keratin molecule in hair consists of many hundreds of amino acid units, arranged in an irregular order, although not a random one by analogy, the letters in this sentence are in an irregular order, but the sentence has meaning. The order in keratin determines how the molecules fit together, giving the hair strength and flexibility.
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