Which Statement About Cystine is CORRECT

Question

Which statement about cystine is CORRECT?
A) Cystine forms when the -CH2-SH R group is oxidized to form a -CH2-S-S-CH2- disulfide bridge between two cysteines.
B) Cystine is an example of a nonstandard amino acid, derived by linking two standard amino acids.
C) Cystine is formed by the oxidation of the carboxylic acid group on cysteine.
D) Cystine is formed through a peptide linkage between two cysteines.
E) Two cystines are released when a -CH2-S-S-CH2- disulfide bridge is reduced to -CH2-SH.

Accepted Answer

Cystine is formed when the sulfur-containing R group of cysteine is oxidized, forming a disulfide bridge between two cysteine molecules (-CHS-S-CHS-). This reaction results in the formation of a non-standard amino acid (cystine) composed of two cysteine residues linked by the disulfide bond.