Download - Curs 3_Nucleul Structura
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Curs 3
Structura Nucleului
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Componente Invelisul nuclear
Carioplasma (nucleoplasma) - sistem
coloidal care include: Cromozomii
Cromatina cu structura fibrilara formata din ADN,
proteine nucleare numite histone, ARN,
fosfolipide Unul sau mai multi Nucleoli cu rol in sinteza
ARN-r si a unor proteine ribozomale
Structura nucleului la Eucariote
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Invelisul nuclear Componente:
doua membrane celulare (intre care se afla
spatiul perinuclear)
- Membrana interna, sustinuta de lamina nucleara(retea interna de filamente atasate de cromatina)
- Membrana externa, in legatura cu RER
Bariera pt. ioni, macromolecule
Membranele formeaza poriAnsamblu complex de proteine
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The nuclear envelope
Components:
Eukaryotic Nucleus - Structure
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Porul nuclear
- Permite transferul unor proteine sintetizate in
citoplasma in interiorul nucleului
- Transportul in citoplasma a ARN sintetizat in
nucleu
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The nuclear pore complex (NPC)
Huge macromolecular complex
Octagonal symmetry
8-fold repetition of subunits
30-50 proteins nucleoporins
Nucleoporins
Symmetrical on both cytoplasmic and nuclear
sides
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The nuclear pore complex (NPC)
Eukaryotic Nucleus - Structure
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Figure 8-72. Freeze-fracture electron micrograph of the elongated nuclear envelope of a fern
spore. Note the ordered arrangement of the nuclear pore complexes in parallel rows. In other
cells either concentrated clusters of nuclear pores or unusual areas free of nuclear pores have
been detected in the nuclear envelope, and these are specifically oriented with respect to othe
structures in the cell. (Courtesy of Don H. Northcote; from K. Roberts and D.H. Northcote,
Microsc.Acta 71:102-120, 1971.)
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Nuclear transport
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The nuclear pore
complex (NPC)
Low molecular wt
solutes
Diffuse freely
Macromolecules
Regulated
Protein import to
nucleus
Nuclear localization signal
(NLS)
Eukaryotic NucleusStructure/Function
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The nuclear pore complex (NPC) Transport receptors karyopherins
Soluble
Importins
Cytoplasm to nucleus
Exportins
Nucleus to cytoplasm
Eukaryotic NucleusStructure/Function
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Import example - nucleoplasmin
Eukaryotic NucleusStructure/Function
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Import example nucleoplasmin
Role of the GTP-binding protein Ran
Active form Ran-GTP
Inactive form Ran-GDP
High concentration of GTP-Ran in nucleus
Low concentration in cytoplasm
Eukaryotic NucleusStructure/Function
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Export RNAs
Move as ribonucleoproteins (RNPs)
Except t-RNA direct transport by exportin-t
Protein component contains nuclear export
signal (NES) Exportins recognize NES
Binds Ran-GTP stabilizes complex
Carried to cytoplasm Ran-GAP1 converts Ran-GTP to Ran-GDP
Eukaryotic NucleusStructure/Function
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Export RNAs
Eukaryotic NucleusStructure/Function
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DNA second structure
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Cromatina
In Cromatina ADN este legat de proteine numite histone,alcatuite din aminoacizi bazici (Arg, Lys)
Histonele formeaza structuri discoidale in jurul carora se
infasoara ADN
Histonele impreuna cu ADN formeaza unitati repetitivenumite NUCLEOZOMI
Nucleosomii se gasesc la intervale de aprox. 200perechi de perechi de baze de pe moleculele de ADN
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20Multiple coiling model
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Basic unit of chromatin-----nucleosomes
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Chromatin type
Euchromatin: open structure
active genes
Heterochromatin: highly packaged
structureinactive genes
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Cromozomii
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Chromosome structure
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Cariotip
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Figure 8-71. Electron micrograph of a mammalian cell nucleus. Note that
the condensed chromatin underlying the nuclear envelope is excluded
from regions around the nuclear pores. (Courtesy of Larry Gerace.)
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Nucleolus- site of rRNAsynthesis and
ribosome assembly
- dynamic stucture,
disappear and rebuild
in the cell cycle
- Fibrillar center FCwhich contains DNA that is not being actively
transcribed
- Dense fibrillar component DFCwhich contains RNA molecules in the processof being synthesized
- Granular componentwhich contains maturing ribosomal precursor
particles
- is not bounded by a membrane
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Nucleolul
Figure 8-65. Electron micrograph of a thin section of a nucleolus in a human fibroblast, showing its
three distinct zones. (A) View of entire nucleus. (B) High-power view of the nucleolus. (Courtesy of
E.G. Jordan and J. McGovern.)
T l i DNA
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Telomeric DNA
The terminal portion of the telomeres ofthe chromosomes contains 10-15kb of
tandem repeats of a 6bp DNA sequence
known astelomeric DNA
.
The telomeric repeat sequences are
necessary for chromosomal integrity inreplication and are added to the
chromosome by a specialized enzyme
known as telomerase.
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Replication
Replication
Replication
TTGGGG
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Replication
Telomerase allows telomere lengthequilibrium maintenance
Telomerase
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Telomere shortening leads to cell death
Cell Death
Replication
Replication
Replication
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Many diseases seen in families withinsufficient telomerase share features of
age-related disease
Bone marrow failure
Immune senescence
Chemotherapy
intolerance
Pulmonary fibrosis
Liver disease
Increased cancer
incidence