A DNA B RNA polymerase C pre-messenger RNA D exons E intron F spliceosome G messenger RNA H excised intron GG nuclear membrane HH nuclear pore I transfer RNA J large ribosomal subunit K small ribosomal subunit L start codon M stop codon N tRNA activation O anticodon P polypeptide chain Q protein primary structure R protein folding S translation T amino acid U amine V carboxyl W residue X excision