( ( The ( primary structure ) ) ( ( consists ( of ( ( two ( long ( nucleotide chains ) ) ) ( that ( are ( ( ( joined ( by ( hydrogen bonds ) ) ) and ) ( ( twisted together ) ( to ( form ( a ( double helix ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (JJ primary) (NN structure)) (VP (VBZ consists) (PP (IN of) (NP (NP (CD two) (JJ long) (NN nucleotide) (NNS chains)) (SBAR (WHNP (WDT that)) (S (VP (VBP are) (VP (VP (VBN joined) (PP (IN by) (NP (NN hydrogen) (NNS bonds)))) (CC and) (VP (VBN twisted) (ADVP (RB together)) (S (VP (TO to) (VP (VB form) (NP (DT a) (JJ double) (NN helix))))))))))))) (. .)))
The primary structure consists of two long nucleotide chains that are joined by hydrogen bonds and twisted together to form a double helix.
(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)))))) (. .)))