<prompt> Which of the following is a modified amino acid?ArginineCysteineAsparagineThreonine  <response>: Two molecules of cysteine make cysteine cys-cys or dithio b, b-a amino propionic acid. The SS linkage is called as disulfide bridge. Ref: Textbook of medical biochemistry, MN Chatterji, 8th edition, page no: 78 