A disulphide bridge in a protein forms between the side chains of two

  • A. cysteine residues
  • B. glycine residues
  • C. lysine residues
  • D. serine residues

Explanation

Two sulphydryl groups are oxidised to form a covalent S-S link, the strongest of the interactions holding tertiary structure. This is why heavy metal ions, which attack sulphur, denature proteins irreversibly. Permanent waving of hair works by breaking and re-forming these bridges in keratin.

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