Which Two Amino Acids Differ from Each Other by Only

Question

Which two amino acids differ from each other by only one atom?
A) Ser and Thr
B) Leu and Ile
C) Ala and Ser
D) Asp and Asn
E) Ser and Cys

Accepted Answer

Serine and cysteine differ by only one atom, with serine having a hydroxyl (-OH) group at its side chain and cysteine having a thiol (-SH) group. The other choices each involve amino acids that differ by more than one atom or group.