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MICR2120 Cell Biology & Disease > The Nucleus > Flashcards

The Nucleus Flashcards

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1
Q

What is the role of the nucleus?

A
  • Maintains integrity of DNA
  • Regulates gene expression
  • Mediates replication of DNA
  • Separates nuclear and cytosolic enzymes
  • Separates sites for transcription and translation
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2
Q

What is the nuclear envelope?

A

Double membrane that encloses entire organelle

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3
Q

What is the nuclear membrane?

A
  • Double lipid bilayer - separates contents of nucelus from cytoplasm.
  • Inner nuclear membrane connected to nuclear lamina
  • Outer nuclear membrane continuous with Rough ER
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4
Q

What are nuclear lamina?

A
  • dense (30-100nm) network inside nucleus

- intermediate filaments and membrane associated proteins

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5
Q

What is the role of the nuclear lamina?

A
  • regulates DNA replication
  • regulates cell devision
  • chromatin organisation
  • anchors NPC in nuclear envelope
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6
Q

What are laminopathies

A

Genetic disorders caused by mutations in genes encoding proteins of the nuclear lamina

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7
Q

What are some common clinical symptoms of laminopathies?

A
  • skeletal dystrophy
  • cardiac muscle dystrophy
  • lipodystrophy
  • progeria
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8
Q

What happens in Emery-Dreifuss muscular dystrophy

A
  • affects skeletal & cardiac muscle
  • contractures in joints
  • cardiac conduction defects
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9
Q

What happens in Hutchinson-Gilford progeria syndrome (HGPS)

A
  • accelerate aging
  • point mutation LMNA gene
  • translated lamin A lacks 50aa
  • LAD50 mutants incorporates abnormally into lamina
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10
Q

What does the LAD50 mutants in HGPS cause?

A
  • thickening of lamina
  • loss of peripheral heterochromatin
  • increased DNA damage
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11
Q

How is genetic material organised in the nucleus?

A

individual patches - chromosome territories

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12
Q

How much DNA does a human cell contain?

A

approx. 2m

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13
Q

How is DNA organised for most of the cell cycle?

A

euchromatin - looser nucleosome, ‘beads on a string’, transcription factors can bind
heterochromatin - compact nucleosome, fibres

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14
Q

What is euchromatin?

A

active DNA, open form, transcription factors bind

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15
Q

What is heterochromatin?

A

inactive DNA

  • constitutive - never expressed, around centromere
  • facultative - differentially expressed (development/stress)
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16
Q

What do insulator elements do in the nucleus?

A

organise chromatin fiber - establish separate compartments of higher-order chromatin structure

17
Q

How do proteins & mRNA transverse the nuclear membrane?

A

nuclear pore complex

18
Q

What size of proteins is NPC freely permeable to

A

<40 kDa

larger need active mechanism & nuclear transport factors

19
Q

What is the NPC?

A
  • 125 mDa
  • embedded into both nuclear membranes
  • cylinder
  • 145nm diameter, 80nm long
  • 69nm channel
  • mammalian NPCs composed 30-60 nucleoporins
20
Q

Organisation of the NPC?

A

8 composite protein rings, cytoplasmic surface and at inner surface
rings connected by spoke proteins

21
Q

How do proteins get into the nucleus?

A
  • NLS recognised by importin complexed with Ran
  • importin binds cytoplasmic filaments
  • translocation, binding pore proteins
  • GEF - GDP on Ran changes to GTP
  • Importin-Ran/GTP complex re-exported
  • GAP hydrolyess to Ran-GDP
22
Q

What are the NLS binding sites of importin alpha?

A
  • monipartite NLS
  • Bipartite NLS
  • usually lysinse or arginine rich
23
Q

What are Nuclear export signals? (NES)

A
  • Leucine rich
  • recognised by receptors, exportins
  • presence of RNA-GTP
  • GTP hydrolysis, dissociation of target protein
24
Q

How can disease be associated with NPC?

A
  • change in NUPs
  • nuclear/cytoplasmic accumulation of material
  • Nup214 mutation - accumulation of protein in nucleus
  • detrimental upregulation of NF-kB, cancer
25
Q

What happens in Triple A syndrome?

A
  • mental retardation
  • adrenal insufficiency
  • muscle control of heart/oesophagus
  • accumulation of ALADIN
26
Q

What does ALADIN (Triple A syndrome) affect the import of?

A
  • Aparataxin
  • DNA ligase I
  • Ferritin heavy chain

normally repair DNA under oxidative dress

27
Q

How do viruses associate with the nuclear pore?

A
  • small viruses able to cross without capsid disassembly

- Large viruses dock to pore via importin B or Nup214

28
Q

How does bulk mRNA exit the nucleus?

A

RNA bound by 1000s of protein - hTREX
marks mRNA ready to be transported
TAP and p15 are exportins

29
Q

What does mRNA nuclear export look like?

A
  • elongates into rod and passes through pore centre

- material rounds into spherical particle on cytoplasmic side

30
Q

What is the consequence of hTREX mutations?

A
  • high grade tumours (aggressive)
  • enhances formation of R loops
  • DNA-RNA hybrid formed
  • R loop stops transcription, increases DNA damage
  • chromosomal lagging

MICR2120 Cell Biology & Disease (17 decks)

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