Cysteine

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Cysteine

Cysteine (pronounced as /sɪˈstiːn/) is a semi-essential proteinogenic amino acid with the formula HO2CCH(NH2)CH2SH. It is encoded by the codons UGU and UGC. The thiol side chain in cysteine often participates in enzymatic reactions, as a nucleophile. The thiol is susceptible to oxidation to give the disulfide derivative cystine, which serves an important structural role in many proteins.

Etymology

The term "Cysteine" comes from the Greek word "kustis" which means bladder. It was first isolated from kidney stones in 1810 by William Prout, but was named by J. Berzelius in 1838 after the natural substance cystine, where it was discovered, which came from the Greek word for bladder, "kustis", and the suffix "-ine" denoting an ingredient.

Structure and properties

Cysteine is a non-essential amino acid, meaning that it can be synthesized by the human body under normal physiological conditions if a sufficient quantity of methionine is available. Cysteine is one of the few amino acids that can form disulfide bonds, and the only one that does so in the human body. This ability is what gives proteins their 3-dimensional structure and their ability to bind to other molecules.

Biological functions

Cysteine plays a crucial role in the metabolism of many organisms. It is involved in the biosynthesis of coenzyme A, glutathione, taurine, and hydrogen sulfide. Cysteine is also involved in the protection of the body from radiation damage and in the detoxification of harmful substances.

Related terms

  • Cystinuria: A genetic disorder that results in poor absorption and high excretion of certain amino acids including cysteine.
  • Cystinosis: A metabolic disease characterized by the abnormal accumulation of the amino acid cystine.
  • Cystine: The oxidized dimer form of cysteine.

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