( ( ( ( ( Arrow heads ) ( indicate ( 3 ' ) ) ) - ) ( ( ( ends and ) arrow ) ( ends ( ( ( the ( 5 ' ) ) - ) ends ) ) ) ) . )
(ROOT (S (S (NP (NNP Arrow) (NNS heads)) (VP (VBP indicate) (NP (CD 3) (POS ')))) (: -) (S (NP (NNS ends) (CC and) (NN arrow)) (VP (VBZ ends) (NP (NP (DT the) (NP (CD 5) (POS '))) (: -) (NP (NNS ends))))) (. .)))
Arrow heads indicate 3'-ends and arrow ends the 5'-ends.
(ROOT (S (NP (JJ Reversible) (NNS reactions)) (VP (VBP are) (VP (VBN indicated) (PP (IN by) (NP (NP (JJ opposite-headed) (NNS kinds)) (PP (IN of) (NP (NNS arrows))))))) (. .)))
Reversible reactions are indicated by opposite-headed kinds of arrows.