This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Amino Acids Basics, Subject name: Biochemistry
Aminoacyl t-RNA is not require for - 
Select and explain. 
A. Proline, B. Lysine, C. Hydroxy lysine, D. Methionine
C: Hydroxy lysine
Answer: C: Hydroxy lysine 
Explanation: Ans. is 'c' i.e., Hydroxylysine o The initial step in protein synthesis is the activation of amino acid in which each of the 20 amino-acids is covalently attached to their respective t-RNA, forming specific amino acyl t-RNA.o The reaction is catalyzed by ami noacyl t-RNA synthase.o Hydroxyproline and hydroxylysine are not represented into genetic code, i.e. they to not have t-RNA capable of accepting them and inserting them into polypeptide chain. Therefore, they have to be synthesized post-translational ly from proline and lysine residues in the polypeptides.