Which of the following amino acids does not include post-translational modification?

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.