( ( This checkpoint ) ( ( ensures ( that ( ( ( anaphase proceeds ) ( ( only when ) ( ( ( the centromeres ) ( of ( all ( sister chromatids ) ) ) ) ( ( lined up ) ( on ( the ( metaphase plate ) ) ) ) ) ) ) ( ( are properly ) ( attached ( to microtubules ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT This) (NN checkpoint)) (VP (VBZ ensures) (SBAR (IN that) (S (NP (NP (JJ anaphase) (NNS proceeds)) (SBAR (WHADVP (RB only) (WRB when)) (S (NP (NP (DT the) (NNS centromeres)) (PP (IN of) (NP (DT all) (JJ sister) (NNS chromatids)))) (VP (VBD lined) (PRT (RP up)) (PP (IN on) (NP (DT the) (JJ metaphase) (NN plate))))))) (VP (VBP are) (ADVP (RB properly)) (VP (VBN attached) (PP (TO to) (NP (NNS microtubules)))))))) (. .)))
This checkpoint ensures that anaphase proceeds only when the centromeres of all sister chromatids lined up on the metaphase plate are properly attached to microtubules.
(ROOT (S (PP (IN During) (NP (DT the) (JJ anaphase) (NN phase))) (, ,) (S (NP (NN sister) (NNS chromatids)) (VP (VBP separate))) (CC and) (S (NP (DT the) (NNS centromeres)) (VP (VBP divide))) (. .)))