methionone - an essential amino acid (See Wikipedia)
threonine - an essential amino acid (See Wikipedia)
tryptophan - an essential amino acid (See Wikipedia)
polypeptide chains - the building blocks of proteins, "a single linear chain of amino acids bonded together by peptide bonds. Protein molecules consist of one or more polypeptides put together typically in a biologically functional way and sometimes have non-peptide" (See Wikipedia)