As atitudes dos alunos para com a Matemática: Um estudo em duas turmas do 6.º ano do Ensino Básico

O presente artigo irá incidir sobre um estudo realizado ao longo do ano letivo de 2017/2018, no âmbito da “Prática de Ensino Supervisionada II” do Mestrado em Ensino do 1.º Ciclo do Ensino Básico e de Matemática e Ciências Naturais no 2.º Ciclo do Ensino Básico. Este estudo teve como objetivo conhecer as atitudes dos alunos de uma turma do 6.º ano do ensino básico para com a Matemática antes e após o período de intervenção, de modo a compará-las e a compreender que aspetos da prática interventiva podem ter influenciado eventuais mudanças de atitude. Para tal, optou-se por uma metodologia quantitativa e, como método de recolha de dados, foram aplicados questionários, com itens fechados e abertos, antes e após o período de intervenção, assim como foram realizadas entrevistas aos alunos que mais diferenças mostraram entre estes dois períodos. Embora não se tenha verificado uma diferença significativa nas atitudes dos alunos para com a disciplina, em termos gerais o grupo evoluiu no que diz respeito a este domínio. Os resultados, para além de mostrarem que os alunos se sentem mais apoiados quando estão mais professoras presentes na sala de aula, também evidenciam que o tipo de atividades que foram desenvolvidas durante o período de intervenção – atividades exploratórias com recurso a materiais manipuláveis – constitui uma motivação extra para que os discentes se envolvam no trabalho matemático em sala de aula.Abstract This article will focus on a study carried out during 2017/2018 academic year, within the scope of the “Supervised Teaching Practice II” of the Master in Teaching in the 1st Cycle of Basic Education and Maths and Science in the 2nd Cycle of Basic Education. This study aimed to know the attitudes of students in a 6th grade class of basic education towards mathematics before and after the intervention period, in order to compare them and to understand which aspects of the interventional practice may have influenced possible changes in attitudes. To this end, a quantitative methodology was chosen and, as a method of data collection, questionnaires were applied, with closed and open items, before and after the intervention period, as well as interviews with students that most showed differences between these two periods. Although there was no significant difference in the students' attitudes towards the discipline, in general terms the group has evolved with respect to this domain. The results, in addition to showing that students feel more supported when there are more teachers present in the classroom, also show that the type of activities that were developed during the intervention period - exploratory activities using manipulable materials - constitutes extra motivation for students to get involved in mathematical work in the classroom.Résumé Cet article se concentrera sur une étude réalisée au cours de l'année académique 2017/2018, dans le cadre de la «Pratique pédagogique supervisée II» du Master en enseignement du 1er cycle de l'enseignement de base et des mathématiques et sciences naturelles du 2e Cycle d'éducation de base. Cette étude visait à connaître les attitudes des élèves d'une classe de base de 6e année à l'égard des mathématiques avant et après la période d'intervention, afin de les comparer et de comprendre quels aspects de la pratique interventionnelle ont pu influencer possibles changements d'attitude. À cette fin, une méthodologie quantitative a été choisie et, comme méthode de collecte des données, des questionnaires ont été appliqués, avec des éléments fermés et ouverts, avant et après la période d'intervention, ainsi que des entretiens avec des étudiants qui ont le plus montré des différences entre cettes deux périodes. Bien qu'il n'y ait pas de différence significative dans les attitudes des étudiants vis-à vis de la discipline, en général le groupe a évolué par rapport à ce domaine. Les résultats, en plus de montrer que les élèves se sentent plus soutenus lorsqu'ils sont plus d'enseignants présents dans la salle de classe, montrent également que le type d'activités développées au cours de la période d'intervention - activités exploratoires utilisant du matériel manipulable - constitue également motivation supplémentaire pour les élèves à s'impliquer dans des travaux mathématiques en classe.info:eu-repo/semantics/publishedVersio

Structural basis of eukaryotic cell targeting by type III secretion system (T3SS) effectors.

International audienceType III secretion systems (T3SS) are macromolecular complexes that translocate a wide number of effector proteins into eukaryotic host cells. Once within the cytoplasm, many T3SS effectors mimic the structure and/or function of eukaryotic proteins in order to manipulate signaling cascades, and thus play pivotal roles in colonization, invasion, survival and virulence. Structural biology techniques have played key roles in the unraveling of bacterial strategies employed for mimicry and targeting. This review provides an overall view of our current understanding of structure and function of T3SS effectors, as well as of the different classes of eukaryotic proteins that are targeted and the consequences for the infected cell

Membrane and chaperone recognition by the major translocator protein PopB of the type III secretion system of Pseudomonas aeruginosa.

International audienceThe type III secretion system is a widespread apparatus used by pathogenic bacteria to inject effectors directly into the cytoplasm of eukaryotic cells. A key component of this highly conserved system is the translocon, a pore formed in the host membrane that is essential for toxins to bypass this last physical barrier. In Pseudomonas aeruginosa the translocon is composed of PopB and PopD, both of which before secretion are stabilized within the bacterial cytoplasm by a common chaperone, PcrH. In this work we characterize PopB, the major translocator, in both membrane-associated and PcrH-bound forms. By combining sucrose gradient centrifugation experiments, limited proteolysis, one-dimensional NMR, and β-lactamase reporter assays on eukaryotic cells, we show that PopB is stably inserted into bilayers with its flexible N-terminal domain and C-terminal tail exposed to the outside. In addition, we also report the crystal structure of the complex between PcrH and an N-terminal region of PopB (residues 51-59), which reveals that PopB lies within the concave face of PcrH, employing mostly backbone residues for contact. PcrH is thus the first chaperone whose structure has been solved in complex with both type III secretion systems translocators, revealing that both molecules employ the same surface for binding and excluding the possibility of formation of a ternary complex. The characterization of the major type III secretion system translocon component in both membrane-bound and chaperone-bound forms is a key step for the eventual development of antibacterials that block translocon assembly

Insights into the specificity of thioredoxin reductase-thioredoxin interactions. a structural and functional investigation of the yeast thioredoxin system

The enzymatic activity of thioredoxin reductase enzymes is endowed by at least two redox centers: a flavin and a dithiol/disulfide CXXC motif. The interaction between thioredoxin reductase and thioredoxin is generally species-specific, but the molecular aspects related to this phenomenon remain elusive. Here, we investigated the yeast cytosolic thioredoxin system, which is composed of NADPH, thioredoxin reductase (ScTrxR1), and thioredoxin 1 (ScTrx1) or thioredoxin 2 (ScTrx2). We showed that ScTrxR1 was able to efficiently reduce yeast thioredoxins (mitochondrial and cytosolic) but failed to reduce the human and Escherichia coli thioredoxin counterparts. To gain insights into this specificity, the crystallographic structure of oxidized ScTrxR1 was solved at 2.4 angstrom resolution. The protein topology of the redox centers indicated the necessity of a large structural rearrangement for FAD and thioredoxin reduction using NADPH. Therefore, we modeled a large structural rotation between the two ScTrxR1 domains (based on the previously described crystal structure, PDB code 1F6M). Employing diverse approaches including enzymatic assays, site-directed mutagenesis, amino acid sequence alignment, and structure comparisons, insights were obtained about the features involved in the species-specificity phenomenon, such as complementary electronic parameters between the surfaces of ScTrxR1 and yeast thioredoxin enzymes and loops and residues (such as Ser(72) in ScTrx2). Finally, structural comparisons and amino acid alignments led us to propose a new classification that includes a larger number of enzymes with thioredoxin reductase activity, neglected in the low/high molecular weight classification491533173326CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP573530/08-407/58147-6; 07/50930-

FtsZ filament capping by MciZ, a developmental regulator of bacterial division.

Cytoskeletal structures are dynamically remodeled with the aid of regulatory proteins. FtsZ (filamentation temperature-sensitive Z) is the bacterial homolog of tubulin that polymerizes into rings localized to cell-division sites, and the constriction of these rings drives cytokinesis. Here we investigate the mechanism by which the Bacillus subtilis cell-division inhibitor, MciZ (mother cell inhibitor of FtsZ), blocks assembly of FtsZ. The X-ray crystal structure reveals that MciZ binds to the C-terminal polymerization interface of FtsZ, the equivalent of the minus end of tubulin. Using in vivo and in vitro assays and microscopy, we show that MciZ, at substoichiometric levels to FtsZ, causes shortening of protofilaments and blocks the assembly of higher-order FtsZ structures. The findings demonstrate an unanticipated capping-based regulatory mechanism for FtsZ

FtsZ filament capping by MciZ, a developmental regulator of bacterial division.

International audienceCytoskeletal structures are dynamically remodeled with the aid of regulatory proteins. FtsZ (filamentation temperature-sensitive Z) is the bacterial homolog of tubulin that polymerizes into rings localized to cell-division sites, and the constriction of these rings drives cytokinesis. Here we investigate the mechanism by which the Bacillus subtilis cell-division inhibitor, MciZ (mother cell inhibitor of FtsZ), blocks assembly of FtsZ. The X-ray crystal structure reveals that MciZ binds to the C-terminal polymerization interface of FtsZ, the equivalent of the minus end of tubulin. Using in vivo and in vitro assays and microscopy, we show that MciZ, at substoichiometric levels to FtsZ, causes shortening of protofilaments and blocks the assembly of higher-order FtsZ structures. The findings demonstrate an unanticipated capping-based regulatory mechanism for FtsZ

Structural insights on the efficient catalysis of hydroperoxide reduction by Ohr: Crystallographic and molecular dynamics approaches

<div><p>Organic hydroperoxide resistance (Ohr) enzymes are highly efficient Cys-based peroxidases that play central roles in bacterial response to fatty acid hydroperoxides and peroxynitrite, two oxidants that are generated during host-pathogen interactions. In the active site of Ohr proteins, the conserved Arg (Arg19 in Ohr from <i>Xylella fastidiosa</i>) and Glu (Glu51 in Ohr from <i>Xylella fastidiosa</i>) residues, among other factors, are involved in the extremely high reactivity of the peroxidatic Cys (C_p) toward hydroperoxides. In the closed state, the thiolate of C_p is in close proximity to the guanidinium group of Arg19. Ohr enzymes can also assume an open state, where the loop containing the catalytic Arg is far away from C_p and Glu51. Here, we aimed to gain insights into the putative structural switches of the Ohr catalytic cycle. First, we describe the crystal structure of Ohr from <i>Xylella fastidiosa</i> (XfOhr) in the open state that, together with the previously described XfOhr structure in the closed state, may represent two snapshots along the coordinate of the enzyme-catalyzed reaction. These two structures were used for the experimental validation of molecular dynamics (MD) simulations. MD simulations employing distinct protonation states and <i>in silico</i> mutagenesis indicated that the polar interactions of Arg19 with Glu51 and C_p contributed to the stabilization of XfOhr in the closed state. Indeed, C_p oxidation to the disulfide state facilitated the switching of the Arg19 loop from the closed to the open state. In addition to the Arg19 loop, other portions of XfOhr displayed high mobility, such as a loop rich in Gly residues. In summary, we obtained a high correlation between crystallographic data, MD simulations and biochemical/enzymatic assays. The dynamics of the Ohr enzymes are unique among the Cys-based peroxidases, in which the active site Arg undergoes structural switches throughout the catalytic cycle, while C_p remains relatively static.</p></div

Representative structures of XfOhr-SH, XfOhr mutants from MD simulations.

<p>(A) Overall representative structure of the XfOhr-SH (cyan), E51A-XfOhr (orange) and R19A-XfOhr (purple) simulations. (B) Active sites of representative structure of the XfOhr-SH (cyan), E51A-XfOhr (orange) and R19A-XfOhr (purple) simulations. Each representative structure corresponds to the MD simulation snapshot closest to the average structure calculated for its trajectory (50 ns). The protein backbone atoms are show in cartoon representation and Arg19/Ala19, Glu51/A1a51, C_p and C_r side chain atoms are shown in stick representation.</p

Proposed model for fatty acid hydroperoxide reduction by Ohr.

<p>(i) In the reduced form of Ohr (C_p-S^-, Cys61 of XfOhr), the thiolate anion (Sɤ of C_p) makes an Hbond with the guanidinium group of the conserved Arg (Arg19 of XfOhr), which also makes a salt-bridge with the conserved Glu (Glu51 of XfOhr). (ii) The lipid hydroperoxide (LHP) is placed over the hydrophobic moiety of the Arg side chain, being also stabilized by other hydrophobic interactions. (iii) After peroxide reduction, C_p is oxidized to sulfenic acid (SOH), which is then attacked by the sulfhydryl group of the resolving Cys (Cys125 of XfOhr), forming an intra-molecular disulfide. Our working hypothesis is that this condensation reaction releases constraints for Arg19 loop movements. (iv) The last step involves the reduction of the disulfide by a lipoylated protein and a rearrangement of the loop to the close state (taken from [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0196918#pone.0196918.ref011" target="_blank">11</a>]). Steps (ii) and (iii) are hypothetical, as substrate and product (respectively) were inserted based on the co-crystallization of PEG with XfOhr [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0196918#pone.0196918.ref011" target="_blank">11</a>].</p