curs 3_nucleul structura

8/13/2019 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



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Import example - nucleoplasmin



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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



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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



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Export RNAs



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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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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

curs 3_nucleul structura

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