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BB10005 > The Nucleus > Flashcards

The Nucleus Flashcards

1
Q

General functions of the nucleus

A

Storage of DNA
DNA to rNA transcription
Mechanical element- stiffer than rest of the cell

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2
Q

How is genetic material arranged in eukaryotes

A

compartmentalised

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3
Q

Benefits of compartmentalisation

A
  • protect DNA
  • incr SA for membrane-localised reactions
  • Incr efficiency of transcription and synthesis
  • More ways to regulate gene expression
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4
Q

Nuclear double membrane: what is it continuous with?

A

Lumen of ER

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5
Q

Nuclear lamina- related to

A

intermediate filaments- most recent common ancestor

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6
Q

Nuclear lamina: location

A

form meshwork on inner nuclear membrane

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7
Q

What does nuclear lamina associate with

A

DNA

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8
Q

Two types of nuclear lamina

A

A/C and B

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9
Q

Nuclear structure: LINC complex

A

Protein complex

Links nuclear lamina with cytoskeleton

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10
Q

LINC proteins on inner membrane (TM)

A

SUN/KASH

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11
Q

LINC proteins on outer membrane (TM)

A

Nesprins, connect to different cytoskeleton elements eg actin- 4 different types

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12
Q

What is the nucleoskeleton/ nuclear matrix made up of

A

NuMa, Titin, Spectrin,PLF, Nuclear actin, Motor proteins

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13
Q

NuMa protein

A

Nuclear mitotic apparatus 1, very large

Organisation of chromatin

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14
Q

Titin protein

A

binds chromosomes and lamina

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15
Q

Spectrin protein

A

Elastic component of lamina

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16
Q

PLF

A

pore linked filaments

important in trafficking

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17
Q

Nuclear actin

A

in form of short filaments or monomers of (G-actin)

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18
Q

Motor proteins

A

Nuclear myosin, kinase

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19
Q

Chromosomes

A

DNA-protein complexes specially packaged for cell division

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20
Q

Chromatin

A

complex of DNA, RNA and proteins

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21
Q

Euchromatin

A 
'true' chromatin
less visible by microscopy
not so densely packed
majority of the genome -90%
localised in central part of the nucleus
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22
Q

Heterochromatin

A

‘different’ chromatin
Looks dark under microscope
Tightly packed condensed DNA
Localised around lamina and nucleoli

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23
Q

What does localisation within the nucleus affect

A

affects whether genes are expressed

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24
Q

Export of RNA and ribosomes

A

mRNA- messenger
rRNA- ribosomal
tRNA- transfer
Assembled ribosomal units

25
Q

Import proteins from the cytoplasm

A

RNA poly
RIbosomal proteins
TFs
Other structural proteins eg lamins

26
Q

Nuclear pore complex

A

Ring structure with 8 fold symmetry
30 different kinds of Nups (nuclear pore proteins)
Central channel filled with FG-Nups that form selective barrier to transport
Common ancestry with COPI, COPII and clathrin
Nuclear side there is a basket, and on the cytosolic side there are fibrils

27
Q

Two kinds of movement through the NPC

A

passive- small molecules and proteins

Facilitated- RNAs, large proteins and macromolecular complexes

28
Q

Energy for facilitated transport from

A

ATP hydrolysis for mRNA

GTP hydrolysis for proteins, tRNA and ribosomes

29
Q

What does facilitated transport require (excluding energy)

A

nucelar transport receptors: karyopherins

30
Q

mRNP

A

mRNA-protein complex

includes proteins tat bind to the mRNA involved in its processing, capping, splicing proteins as well as export factors

31
Q

How can mRNP get in and out

A

through NPC

32
Q

What does ATP hydrolysis do in mRNP transport through NPC

A

Release of Dbp5 in cytoplasm and mRNP remodelling so it can’t go back in because not energetically favourable

33
Q

Another name for karyopherins

A

Importins

34
Q

Karyopherins

A

bind cargo proteins in cytoplasm- recognise NLS
Interact with FG-Nups
Move through NPC and release cargos in nucleus

35
Q

What is cargo release enabled by (importin)

A

Ran-GTP binding to importin- Beta

conformational change that results in complex coming apart

36
Q

Exportins

A

Bind cargo proteins in the nucleus when they (the exportin) are bound to Ran-GTP
Interact with FG-Nups
Release cargos in cytoplasm

37
Q

What is cargo loading enabled by

A

Ran GTP binding to exportin
Conformational change that results in complex assembly
Ran GTP hydrolysed to Ran GDP in cytoplasm for dissociation

38
Q

GTPases

A

molecular switches

bind GTP, hydrolyse a phosphate to form GDP

39
Q

What type of Ran in the cytosol

A

Ran-GAP

40
Q

What type of Ran in the nucleus

A

Ran-GEF

41
Q

GAP assists

A

GTP hydrolysis to GDP

useful diagram

42
Q

GEF assists

A

GTP loading after hydrolysis

43
Q

NLS

A 
nuclear localisation sequence
8 AAs long
Can occur anywhere in a protein
Lysine (K), arginine (R) and Proline (P)
binds to importins
44
Q

NES

A

nuclear export signal

Sequence with 4 hydrophobic AAs (most often leucine, L)

45
Q

How can NLS and NES be modified

A

phosphorylation etc

46
Q

nucleoli

A

little nuclei not visible under microscope

no membranes

47
Q

Nucleolus

A

cells can have 1 large nucleolus or many small nucleoli

48
Q

Nucleolus major functions

A

Transcription of rRNAs

Assembly of ribosomal subunits

49
Q

Nucleolus composed of

A

segments of 10 chromosomes encoding rRNA genes
Proteins for processing rRNAs
Ribosomal subunit proteins
SnoRNA (small nucleolar RNA)

50
Q

SnoRNA

A

oligonucleotides that help process rRNA

51
Q

Other functions nucleolus

A

sensing and responding to stress

Cell cycle regulation- cancer it goes worong

52
Q

Cajal bodies

A

RNA processing
Genome organisation
Dense foci of coilin protein- resemble coiled balls of yarn under EM

53
Q

PML bodies

A

Associated often with cajal bodies

DNA repair, cell proliferation, programmed cell death

54
Q

Speckles

A 
Gene transcription
mRNA processing (splicing )
55
Q

Evolution of the nucleus theory

A

DNA in ancient prokaryotic cell tethered to membrane
Over time tethering increased till nucleus bound DNA
Evidence for this theory- a lot of the proteins found linking the DNA to the inner mem have evol relationships to COP proteins involved in trafficking

56
Q

Mutations in lamins give rise to

A

laminopathies
muscular cystrophy and progeria
result from mechanical failure as without lamina don’t have structural protection

57
Q

what are euchromatin and heterochormatin also referred to as

A

A/B chromatin

58
Q

LADs

A

lamina associated domains

59
Q

Level of RNA production in LADs

A

less RNA production in LADs (ie where heterochromatin is) than away from lamins (euchromatin)

BB10005 (27 decks)

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