The amino acid that is cyclic and identified as the exception to the common α-amino acid structure is _____.
Answer
proline
Explanation
Proline is identified as the cyclic amino acid and exception to the common α-amino acid structure described in the notes. Its distinctive ring structure differentiates it from the usual open side-chain examples. **Key takeaway:** Proline is the structural exception highlighted in the material. **Glossary:** Cyclic: arranged as a ring.