[Campbell Biology P.126] Which of the following amino acids, as depicted in Figure 5.14, pos... | Practice Question

Which of the following amino acids, as depicted in Figure 5.14, possesses a cyclic side chain that incorporates part of the main amino acid backbone, making it unique among the 20 common amino acids?

  • A: Tryptophan
  • B: Proline
  • C: Histidine
  • D: Phenylalanine

Explanation

Proline is unique among the 20 common amino acids because its side chain forms a five-membered ring with its alpha-amino group, effectively making it an imino acid rather than an amino acid. This cyclic structure incorporates part of the main amino acid backbone.