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(ROOT (S (NP (NNP INTRODUCTION) (NNP Lipids)) (VP (VBP play) (NP (DT an) (JJ essential) (JJ structural) (NN role)) (PP (PP (IN as) (NP (NP (DT a) (NN barrier)) (PP (IN between) (NP (NN intra) (CC and) (NN extracellular) (NN medium))))) (CC and) (PP (IN as) (NP (NP (DT a) (NN matrix)) (VP (VBG providing) (NP (NP (DT a) (JJ suitable) (JJ hydrophobic) (NN environment)) (PP (IN for) (NP (JJ membrane) (NNS proteins))))))))) (. .)))
INTRODUCTION Lipids play an essential structural role as a barrier between intra and extracellular medium and as a matrix providing a suitable hydrophobic environment for membrane proteins.
(ROOT (S (NP (NP (DT A) (NN cell) (POS 's)) (NN membrane)) (VP (VBZ provides) (NP (DT a) (NN barrier) (S (VP (TO to) (VP (VB keep) (NP (NN extracellular) (NNS materials)) (PP (IN from) (S (VP (VBG mixing) (PP (IN with) (NP (PRP$ its) (JJ internal) (NNS components))))))))))) (. .)))