To understand the role of bile acids (BAs) in cell function, many authors have investigated their effect on biomembrane models which are less complex systems, but there are still many open questions. The present study aims to contribute for the deepening of the knowledge of the interaction between BAs and model membranes, in particular, focusing on the effect of BA mixtures. The cytotoxic deoxycholic acid (DCA), the cytoprotective ursodeoxycholic acid (UDCA), and the equimolar mixture (DCA + UDCA) were investigated. Monolayers and liposomes were taken as model membranes with two lipid compositions: an equimolar mixture of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), sphingomyelin (SM), and cholesterol (Chol)) traditionally associated with the formation of lipid rafts and an equimolar POPC/SM binary mixture. The obtained results showed that DCA causes the fluidization of monolayers and bilayers, leading to the eventual rupture of POPC/SM liposomes at high concentration. UDCA may provide a stabilization of POPC/SM membranes but has a negligible effect on the Chol-containing liposomes. In the case of equimolar mixture DCA/UDCA, the interactions depend not only on the lipid composition but also on the design of the experiment. The BA mixture has a greater impact on the monolayers than do pure BAs, suggesting a cooperative DCA-UDCA interaction that enhances the penetration of UDCA in both POPC/SM and POPC/SM/Chol monolayers. For the bilayers, the presence of UDCA in the mixture decreases the disturbing effect of DCA.

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Resumo -Este artigo procura analisar o estudo da cidade nos actuais programas de Geografia e nalguns manuais escolares em vigor. Com a reorganização curricular da Geografia verificamos que, agora, a dimensão mais valorizada, é o desenvolvimento de competências essenciais e menos a memorização de conteúdos. Os novos manuais escolares editados vão responder ao desafio de fazer uma Geografia capaz de contribuir para a formação de cidadãos geograficamente competentes. O estudo da cidade continua a fazer parte importante do novo currículo da Geografia, mas verificam-se poucas alterações em relação aos conteúdos que eram abordados antes da reorganização, pelo menos naquilo que se refere à forma como os manuais escolares abordam este tema. Palavras-chave:Cidade, geografia escolar, reorganização curricular, manuais escolares.Abstract -TEACHING ABOUT THE CITY IN COMPULSORY SCHOOL. This paper aims at analysing the study of the city in today's Geography programmes and some textbooks currently in use. The recent curricular reform in Geography has bought a new approach to the subject: the most important issue is now the development of essential skills, contrary to former programmes of study more centred on the memorisation of scientific content. Geography textbooks have also been reformulated in order to adequately respond to this challenge of educating geographically skilled citizens. The study of the city remains an important part of this new Geography curriculum, but few changes have been made considering the scientific content in the previous curricula, at least in the way textbooks approach this subject.

The contribution of geography education to citizenship education is recognized by geography educators. Still, globalization created new territories and new "borders" not always easy to cross-but they all exist and coexist giving new meanings to the idea of space appropriation. Geographical space has gained all these dimensions and can no longer be viewed in terms of its materiality. This article addresses the concept of citizenship education for Portuguese geography teachers within the multicultural nature of Portuguese society and schools. A final reference is given to the importance of cities as places of citizenship education.