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3.nucleus.cell biology

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mohammad mir mohammadi
mohammad mir mohammadi

The nuclear envelope contains an inner and outer membrane, separated by the perinuclear space. It regulates transport between the nucleus and cytoplasm. The nuclear lamina lies underneath the inner nuclear membrane and provides structural support. Nuclear pore complexes control molecular traffic through the envelope. Small molecules can passively diffuse, while larger cargoes require transport receptors and Ran GTPase. Importins ferry proteins into the nucleus via nuclear localization signals, while exportins use nuclear export signals and RanGTP to transport proteins and RNAs out of the nucleus. This ensures proper distribution and functions of biomolecules in the cell.

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Cell BiologyCell Biology S. Rahgozar,PhD University of Isfahan Faculty of Science 3. The nucleus 3.1. The nuclear envelope and nuclear traffic 1392-93
 Structure of the nuclear envelope The space between the inner and outer nuclear membranes is directly connected with the lumen of the endoplasmic reticulum.
 Nuclear membrane Compared to ER membrane is  Similar in Function having ribosomes bound to its surface)  Different in composition (outer membrane contains proteins that bind to cytoskeleton and inner membrane carries specific proteins (ie; those bound to nuclear lamina)
Nuclear membranes are permeable to small non polar molecules. Small polar molecules Macromolecules Ions May pass through pores  Nuclear lamina Contains 60-80kd fibrous proteins called lamins Function: structural support of the nucleus
Model of lamin assembly At least 7 distinct proteins of lamins are coded from 3 lamin genes of A, B and C
o Laminar modifications Post translational addition of specific types of lipids (prenylation)
o Laminar interactions  Histones H2A and H2B
 LBR (lamin B receptor) and Emerin  Nuclear proteins that function in DNA synthesis, transcription or chromatin
 Nuclear pore complex  Diameter: 120 nm  Molecular mass: 125,000 kd  Composed of 30 proteins (nucleoporins) in multiple copies (~30×the size of a ribosome)Molecular traffic through nuclear pore complexes (20-40 kd)
Model of the nuclear pore complex o A structure with 8fold symmetry organised around a large central channel
Nuclear localization signals (1984, Smith, Cell. studying SV40 T Ag)  Selective transport of proteins o Nuclear localization signals (specific aa sequences) o Nuclear transport receptors (importins) Involved in replication Involved in chromatin assembly bipartite
Distribution of Ran/GTP across the nuclear envelope Examples for Small GTP binding proteins: Ran, Rab, Rac, Rho, Cdc42, Arf, Ran GAP: Ran GTPase activating protein Ran GEF: Ran guanine nucleotide exchange factor
Protein import through the nuclear pore complex NLS: nuclear localization sequence Transport proceeds by sequential binding to specific nuclear pore proteins located further and further toward the nuclear side of the pore complex. FG- proteins After release of importin Ran/GDP is transported back to the nucleus by NTF2 receptor
Nuclear export NES: nuclear export sequence  exportins and importins are members of a family named karyopherins  Ran/GTP promotes the formation of stable complexes between exportins and their cargo proteins Whereas It dissociates the complexes between importins and their cargos
3.nucleus.cell biology
 Regulation of nuclear protein import  Inhibition by binding to a cytoplasmic inhibitory factor which masks its NLS ubiquitin-mediated Cell stimulation  Inhibition by direct phosphorylation of NLS
 Transport of RNAs Transport of a ribonucleoprotein complex (RNP) of 35-40kb from the nuclear pore in the salivary gland of an insect (A), and unfolding of the RNA during its translocation to the cytoplasm N C  Transport of tRNAs, rRNAs, miRNAs and snRNAs is through Ran/GTP  Transport of mRNAs in through mRNA exporter (a complex of two proteins including NTF2)
o tRNAs and miRNAs are exported by exportin-t and exportin5 Functional snRNP snRNP: small nuclear ribonucleoprotein 5’7mGcap: 5’ 7- methylguanosine cap o Small RNAs function within the nucleus as components of the RNA processing machinery.

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3.nucleus.cell biology

  • 1. Cell BiologyCell Biology S. Rahgozar,PhD University of Isfahan Faculty of Science 3. The nucleus 3.1. The nuclear envelope and nuclear traffic 1392-93
  • 2.  Structure of the nuclear envelope The space between the inner and outer nuclear membranes is directly connected with the lumen of the endoplasmic reticulum.
  • 3.  Nuclear membrane Compared to ER membrane is  Similar in Function having ribosomes bound to its surface)  Different in composition (outer membrane contains proteins that bind to cytoskeleton and inner membrane carries specific proteins (ie; those bound to nuclear lamina)
  • 4. Nuclear membranes are permeable to small non polar molecules. Small polar molecules Macromolecules Ions May pass through pores  Nuclear lamina Contains 60-80kd fibrous proteins called lamins Function: structural support of the nucleus
  • 5. Model of lamin assembly At least 7 distinct proteins of lamins are coded from 3 lamin genes of A, B and C
  • 6. o Laminar modifications Post translational addition of specific types of lipids (prenylation)
  • 7. o Laminar interactions  Histones H2A and H2B
  • 8.  LBR (lamin B receptor) and Emerin  Nuclear proteins that function in DNA synthesis, transcription or chromatin
  • 9.  Nuclear pore complex  Diameter: 120 nm  Molecular mass: 125,000 kd  Composed of 30 proteins (nucleoporins) in multiple copies (~30×the size of a ribosome)Molecular traffic through nuclear pore complexes (20-40 kd)
  • 10. Model of the nuclear pore complex o A structure with 8fold symmetry organised around a large central channel
  • 11. Nuclear localization signals (1984, Smith, Cell. studying SV40 T Ag)  Selective transport of proteins o Nuclear localization signals (specific aa sequences) o Nuclear transport receptors (importins) Involved in replication Involved in chromatin assembly bipartite
  • 12. Distribution of Ran/GTP across the nuclear envelope Examples for Small GTP binding proteins: Ran, Rab, Rac, Rho, Cdc42, Arf, Ran GAP: Ran GTPase activating protein Ran GEF: Ran guanine nucleotide exchange factor
  • 13. Protein import through the nuclear pore complex NLS: nuclear localization sequence Transport proceeds by sequential binding to specific nuclear pore proteins located further and further toward the nuclear side of the pore complex. FG- proteins After release of importin Ran/GDP is transported back to the nucleus by NTF2 receptor
  • 14. Nuclear export NES: nuclear export sequence  exportins and importins are members of a family named karyopherins  Ran/GTP promotes the formation of stable complexes between exportins and their cargo proteins Whereas It dissociates the complexes between importins and their cargos
  • 16.  Regulation of nuclear protein import  Inhibition by binding to a cytoplasmic inhibitory factor which masks its NLS ubiquitin-mediated Cell stimulation  Inhibition by direct phosphorylation of NLS
  • 17.  Transport of RNAs Transport of a ribonucleoprotein complex (RNP) of 35-40kb from the nuclear pore in the salivary gland of an insect (A), and unfolding of the RNA during its translocation to the cytoplasm N C  Transport of tRNAs, rRNAs, miRNAs and snRNAs is through Ran/GTP  Transport of mRNAs in through mRNA exporter (a complex of two proteins including NTF2)
  • 18. o tRNAs and miRNAs are exported by exportin-t and exportin5 Functional snRNP snRNP: small nuclear ribonucleoprotein 5’7mGcap: 5’ 7- methylguanosine cap o Small RNAs function within the nucleus as components of the RNA processing machinery.