Cysteine

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 * Cysteine ** (abbreviated as ** Cys ** or ** C ** ) [|[2]] is an α- [|amino acid] with the [|chemical formula] HO2CCH(NH2)CH2SH. It is a semi- [|essential amino acid], which means that it can be [|biosynthesized] in humans. [|[3]] Its [|codons] are UGU and UGC. Cysteine was considered to be a [|hydrophilic] amino acid based on the belief that the [|thiol group] interacts well with water. However, the cysteine side chain participates in the hydrophobic bonding system of the micelle. The quantitative comparison of the values of the [|critical micelle concentrations] leads to the conclusion that the CH2SH group of amino acid has the same effect on the [|micelle] stability as a methylene group of the [|hydrocarbon] tail. Therefore, there is justification for the recently voiced assumptions of the hydrophobic nature of the cysteine side chain in proteins. [|[4]][|[5]][|[6]] [|[7]] The thiol side chain often participates in [|enzymatic] reactions, serving as a [|nucleophile] . The thiol is susceptible to oxidization to give the [|disulfide] derivative [|cystine] , which serves an important structural role in many [|proteins] . When used as a food additive, it has the [|E-number] [|E920].
 * ~ Properties[|[1]] ||
 * [|Molecular formula] || C 3 H 7 NO 2 S ||
 * [|Molar mass] || 121.16 g mol −1 ||
 * Appearance || white crystals or powder ||
 * [|Melting point] || 240 °C decomp. ||
 * [|Solubility] in [|water] || soluble ||
 * [|Chiral rotation] [α] D || +9.4° (H 2 O, //c// = 1.3) ||

Cysteine is an amino acid, a building block of proteins that are used throughout the body and can be broken down to a antioxidant. Antioxidants fight free radicals, harmful compounds in the body that damage cell membranes and DNA. Researchers think free radicals play a role in aging as well as the development of a number of health problems, including heart disease and cancer. It can help prevent side effects caused by drug reactions and toxic chemicals, and helps break down mucus in the body. It seems to have benefits in treating some respiratory conditions like bronchitis.   