This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Basics of amino acids, Subject name: Biochemistry
Non-protein amino acid is 
Select and explain. 
A. Aspaate, B. Histidine, C. Ornithine, D. Tyrosine
C: Ornithine
Answer: C: Ornithine 
Explanation: Non-protein amino acids are those found in our body but not incorporated into proteins. They are not coded by codons. Example of non-protein amino acids: Ornithine Citrulline Homocysteine Beta-alanine GABA Sarcosine Homoserine