This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Which of the following amino acids does not include post-translational modification? 
Select and explain. 
A. Selenocysteine, B. Triiodothyronine, C. Hydroxyproline, D. Hydroxylysine
A: Selenocysteine
Answer: A: Selenocysteine 
Explanation: Ans. A. SelenocysteinePeptidyl selenocysteine is not the product of a posttranslational modification, but is inseed directly into a growing polypeptide during translation. Selenocysteine is commonly termed as the "21st amino acid." However, incorporation of selenocysteine is specified by a large and complex genetic element for the unusual tRNA called tRNASec which utilizes the UGA anticodon that normally signals STOP.