Selenocysteine,N-Formylmethionine and Pyrrolysine Are Found in Many Proteins

Multiple Choice

Selenocysteine,N-formylmethionine and pyrrolysine are found in many proteins.These amino acids are considered standard amino acids along with 20 common amino acids because they

A) are incorporated into proteins from specific codons.
B) are formed by post-translational modifications.
C) play key roles in metabolism.
D) are precursors of other important amino acids.