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Este Caderno contém 05 questões discursivas referentes à Prova da Língua Estrangeira escolhida
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Assinatura do Candidato: _________________________________________________
As questões de 01 a 05, cujas respostas deverão ser redigidas EM PORTUGUÊS, referem -se
ao texto abaixo.
Where do we go in the nucleus?
Stan Fakan and Roel Van Driel
The nucleus contains the genetic patrimony of the cell, protects it against environmental
stress, and ensures its repair, and its duplication and transcription. The nucleus is limited by a
well defined nuclear envelope. In contrast to cytoplasmic compartments, membranes do not limit
nuclear compartments. However, after four decades of extensive investigations, many nuclear
domains have been morphologically defined and some have been functionally characterized.
The best example is the nucleolus, which is responsible for rRNA syn thesis and the assembly of
ribosomal subunits. The relationships between the structure of the nucleolus and its functions
have been relatively well established. As to nucleoplasmic compartments, many have been
morphologically characterized, but their funct ions are often only partially understood or are still
elusive. This includes a variety of nuclear bodies, which are often characterized by the presence
of specific proteins, but their role in nuclear functions still remains to be revealed.
The most intensively studied nuclear component is chromatin. The complete DNA sequence
of an increasing number of organisms is known, defining the genetic level of genome function.
At the chromatin level, we begin to understand the pattern of histone modifications, DNA
methylation and chromatin remodelling, together determining the epigenetic level of gene
expression. Nuclear architecture is tightly related to chromatin function. Chromatin is present in
different structural and functional states. The quantitatively most im portant state is condensed
chromatin, defining chromatin domains in the nucleus. Electron microscopy allows one to
observe dispersed chromatin fibers at the periphery of such chromatin domains. An interphase
chromosome territory consists of an ensemble of chromatin domains. This large-scale chromatin
organization is directly related to genomic activity. The border regions of condensed chromatin,
named the perichromatin region, are the sites of both transcription and replication. No such
activity can be detected inside condensed chromatin domains.
Nascent transcripts can be visualized as perichromatin fibrils. Transcription factors and RNA
processing machineries are found in the same perichromatin compartment. In addition, RNA
processing factors are also concentrated in special nucleoplasmic compartments, such as
clusters of interchromatin granules (speckles). This domain is probably a site of factor storage
or assembly of splicing complexes, as suggested by elegant in vivo experiments, but is not a
site of transcription. RNA processing factors can be recruited from these domains to sites of
transcription. Another nuclear domain in which processing factors accumulate is the Cajal
(coiled) body, which has been shown to move rapidly inside the nucleus. The Cajal (coiled) body
is found in close proximity of the U2 snRNA locus, suggesting it has some role in snRNA
metabolism.
Many studies support the idea that macromolecules, such as protein factors, freely diffuse
inside the nucleus. Also, chromatin shows a constra ined type of free diffusion, transcriptionally
active chromatin more so than transcriptionally silent chromatin. Chromatin movement is
relatively local, since it has been shown that complete chromosomes do not move. In contrast,
nucleoli have been reported to travel throughout the nucleoplasm. Evidently, the cell nucleus is
highly dynamic at different levels of organization. The molecular details await further analysis of
the basics of the molecular organization of the nucleus. In line with this, RNP comple x migration
would take place by free diffusion from the site of RNA synthesis to the nuclear pores.
To understand basic processes, such as orchestrating the expression of large numbers of
genes, replication of the genome and DNA repair, we need to understa nd the dynamic spatial
organization of the nucleus at the molecular level. A major enigma is how the chromatin fiber is
folded and how this gives rise mainly to condensed chromatin domains. An immediately related
question is how transcriptionally active ch romatin is positioned exclusively in the perichromatin
region and how nascent, replicated DNA is in the same compartment. Another enigma is the
function of the large amount of RNA that never leaves the nucleus. A solution to this question
may come from ongoing work on the function of many types of non -protein coding RNA,
including, for instance, gene controlling microRNAs and what appears to be structural RNAs,
such as Xist. The association of intranuclear lipids with active chromatin is also intriguing. We
expect that this issue of Biology of the Cell will contribute to the generation of new ideas and will
be a valuable support for further work on functional architecture of the nucleus.
Disponível em:< www.elsevier.com/locate/biocell>. Acesso em: 18 jun. 2011.
UFRN – Exame de Proficiência 2011_2 – Inglês – Ciências Biológicas
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Questão 1
De acordo com o texto, como se caracteriza o núcleo de uma célula?
Espaço para Resposta
Questão 2
O que o estudo do componente nuclear cromatina permitiu compreender?
Espaço para Resposta
UFRN – Exame de Proficiência 2011_2 – Inglês – Ciências Biológicas
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Questão 3
Descreva os dois domínios nucleares citados no terceiro parágrafo.
Espaço para Resposta
Questão 4
Quais os enigmas que ainda envolvem o componente nuclear cromatina?
Espaço para Resposta
UFRN – Exame de Proficiência 2011_2 – Inglês – Ciências Biológicas
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Questão 5
 Traduza o fragmento textual abaixo no espaço reservado para isso.
 Seu texto deverá apresentar clareza e estar bem articulado tanto em termos estruturais
quanto de sentido.
Chromatin
movement
is
relatively
local, since
it
has
been shown
that complete
chromosomes do not move. In contrast, nucleoli have been reported to travel throughout the
nucleoplasm. Evidently, the cell nucleus is highly dynamic at different levels of organization.
The molecular details await further analysis of the basics of the molecular organization of
the nucleus. In line with this, RNP complex migration would take place by free diffusion from
the site of RNA synthesis to the nuclear pores.”
ESPAÇO DESTINADO AO TEXTO DEFINITIVO
UFRN – Exame de Proficiência 2011_2 – Inglês – Ciências Biológicas
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