Question

Choose the correct combination of statements given below related to the cysteine residue in proteins.
i) Cysteine can be linked to tyrosine by $S-O$ bond.
ii) Cysteine can be linked to another cysteine by $S-S$ bond.
iii) Cysteine can complex with $Z{n}^{2+}$.
iv) Cysteine can be linked to methionine by $S-S$ bond.

• A. i) and ii)
• B. ii) and iii)
• C. iii) and iv)
• D. i) and iv)

Answer 1

Answer: (B)

ii) and iii)

Cysteine is a semi-essential proteinogenic amino acid. It is one of the 20 naturally occurring, 'biogenic' amino acids which link by peptide bonds to form polypeptides and proteins. Cysteine can be easily oxidized to form a dimer containing disulfide bridge (S-S)between two cysteines. Such a dimer is known as cysteine. Disulfide bonds in proteins are formed by the process of oxidative folding. The other sulfur-containing amino acid, methionine, cannot form disulfide bonds. Many other metal cofactors in enzymes are bound to the substituent of cysteinyl residues. Examples include zinc, copper, iron and nickel.

So, the answer is B (ii and iii).