Cysteine

Cysteine is a sulfur-containing amino acid incorporated into proteins. Its thiol group can form disulfide bonds that stabilize protein structures.

Amino acid: An organic molecule with amino and carboxyl groups that serves as a protein building block. Cysteine is one of the amino acids incorporated into proteins.
Disulfide bond: A covalent bond between two sulfur atoms, commonly formed by oxidation of two thiol groups. Two cysteine side chains form this bond, which can stabilize a protein’s folded structure.
N-acetylcysteine: A derivative of cysteine used as a medication and as a precursor for glutathione synthesis. It supplies cysteine for glutathione production and is used to treat acetaminophen overdose.
Genetic code: The mapping between nucleotide sequences in messenger RNA and amino acids in proteins. Cysteine is assigned two codons, UGU and UGC, within this shared mapping.
Thiol: A functional group consisting of a sulfur atom bonded to a hydrogen atom. Cysteine’s thiol group enables its characteristic redox chemistry and bond formation.
Protein folding: The process by which a protein adopts its functional three-dimensional structure. Cysteine disulfide bonds can constrain folding and stabilize the resulting structure.
Cystinuria: An inherited disorder in which impaired kidney transport causes excessive urinary loss of cystine and other amino acids. Cystine, the oxidized disulfide form of cysteine, accumulates in urine and can form stones.
Methionine: An essential sulfur-containing amino acid that initiates most protein synthesis and supplies methyl groups through metabolism. Methionine metabolism can contribute to cysteine production in animals.
Codon: A sequence of three nucleotides that specifies an amino acid or a translation stop signal. The UGU and UGC codons specify cysteine during protein synthesis.
Redox reaction: A chemical reaction involving electron transfer and changes in oxidation state. Forming a disulfide oxidizes cysteine thiols; breaking it reduces them.

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