( We ( ( ( have already ) ( mentioned ( that ( DNA ( is ( ( a ( double helix ) ) ( consisting ( of ( ( two ( interwound chains ) ) ( of ( ( building blocks ) ( called nucleotides ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP We)) (VP (VBP have) (ADVP (RB already)) (VP (VBN mentioned) (SBAR (IN that) (S (NP (NNP DNA)) (VP (VBZ is) (NP (NP (DT a) (JJ double) (NN helix)) (VP (VBG consisting) (PP (IN of) (NP (NP (CD two) (JJ interwound) (NNS chains)) (PP (IN of) (NP (NP (NN building) (NNS blocks)) (VP (VBN called) (NP (NNS nucleotides)))))))))))))) (. .)))
We have already mentioned that DNA is a double helix consisting of two interwound chains of building blocks called nucleotides .
(ROOT (S (NP (DT The) (JJ double) (NN helix) (NN dna) (NN shape)) (VP (VBZ forms) (SBAR (WHADVP (WRB when)) (S (NP (DT the) (CD two) (JJ nucleotide) (NNS chains)) (VP (VB wrap) (PRT (RP around)) (NP (DT the) (JJ same) (NNS axis)))))) (. .)))