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Cysteine
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A metabolic pathway diagram for Escherichia coli showing how various nutrients-including sugars, fats, glycerol, and amino acids-are broken down into intermediates like pyruvate and acetyl-CoA, leading to the production of energy and other metabolites such as lactate, glutamate, and succinate. Arrows indicate the flow of metabolites between compounds, with key nutrient sources and products highlighted in colored boxes. Figure 1A: Structures of amino acids glycine, alanine, serine, cysteine, and cystine.
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Amino acid
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Cysteine

amino acid
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Cysteine, Sulfur-containing nonessential amino acid. In peptides and proteins, the sulfur atoms of two cysteine molecules are bonded to each other to make cystine, another amino acid. The bonded sulfur atoms form a disulfide bridge, a principal factor in the shape and function of skeletal and connective tissue proteins and in the great stability of structural proteins such as keratin.

This article was most recently revised and updated by Kara Rogers.