( ( ( ( Polypeptides , ) ( ( the precursors ) ( of proteins ) ) ) , ) ( ( are ( chains ( of ( amino acids ) ) ) ) . ) )
(ROOT (S (NP (NP (NNS Polypeptides)) (, ,) (NP (NP (DT the) (NNS precursors)) (PP (IN of) (NP (NNS proteins)))) (, ,)) (VP (VBP are) (NP (NP (NNS chains)) (PP (IN of) (NP (JJ amino) (NNS acids))))) (. .)))
Polypeptides, the precursors of proteins, are chains of amino acids.
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (JJ amino) (NNS acids)) (VP (VBZ bind) (ADVP (RB together))))) (, ,) (NP (PRP they)) (VP (VBP form) (SBAR (S (NP (DT a) (JJ long) (NN chain)) (VP (VBD called) (NP (NP (DT a) (-LRB- -LRB-) (NN n) (-RRB- -RRB-) (NN polypeptide)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBZ is) (NP (NP (DT an) (JJ essential) (NN component)) (PP (IN of) (NP (NN protein)))))))))))) (. .)))