= 'true' chromatin - less densely packed - majority of genome - localised in central part of nucleus

Nucleus Flashcards by Rosie Liddell

What are the general functions of the nucleus?

> storage of DNA
transcription of RNA from DNA
mechanical element
- stiffer than rest of cell so limiting factor in how squashed a cell can get

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What are the benefits of compartmentalisation of genetic material in eukaryotes?

> protect DNA from reactions in cell - enzymes
increase SA for membrane-localised reactions
increase efficiency of transcription & synthesis
more ways to regulate gene expression

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How many nuclei do cells have?

Most have 1
Red blood cells = 0
Skeletal muscle = many

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Describe the nuclear membrane

Double membrane

- contiguous w/ lumen of ER

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What is the ER the site of?

Protein production by ribosomes, protein folding & glycosylation

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What is the theory for the evolution of the nucleus?

DNA in ancient prokaryotic cell was tethered to membrane until it became bound to membrane bound ribosomes

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What are nuclear lamina?

> structure composed of nuclear lamins

> dense fibrillar network inside the nucleus

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What are nuclear lamins?

> related to intermediate filaments
structural: form meshwork on inner nuclear membrane
functional: associate w/ DNA
2 types: A/C & B

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What can mutations in lamins lead to?

‘Laminopathies’

–> muscular dystrophy & progeria (premature ageing)

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What is the LINC complex?

Protein complex that links nuclear lamina w/ cytoskeleton

Inner membrane: SUN/KASH proteins

Outer membrane: nesprins
(connect to diff cytoskeleton elements)
(4 types w/ structural & functional roles)

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What is the nuclear matrix?

Network of fibres found throughout the inside of a nucleus

- analogous to a cytoskeleton (‘nuceloskeleton’)

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What is the nuclear matrix composed of?

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

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In what 2 forms is DNA arranged within the nucleus?

Chromosomes
= DNA-protein complexes specially packaged for cell division

Chromatin
= complex of DNA, RNA & proteins

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What are the 2 types of chromatin?

> Euchromatin

> Heterochromatin

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Describe euchromatin

= ‘true’ chromatin

less densely packed
majority of genome
localised in central part of nucleus

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Describe heterochromatin

= ‘different’ chromatin

dark under microscope
tightly packed condensed DNA
localised around lamina & nucleoli

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How is DNA organised within the nucleus?

Chromosomes exist in discrete territories within nucleus

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What does localisation of DNA within the nucleus affect?

Whether gees are expressed (=transcribed into RNA)

Less RNA production in LADs (heterochromatin) than away from lamina (euchromatin)

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What are LADs?

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Lamina-associated domains

How does info get out of the nucleus?

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Export of RNA & ribosomes

- mRN, rRNA, tRNA & assembled ribosomal units

Which proteins need importing into the nucleus?

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RNA polymerase
Ribosomal proteins
Transcription factors
All other structural proteins (lamins, histones etc)

Through which structure do proteins move in & out of the nucleus?

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Nuclear Pore Complex (NPC)

What are the features of NPCs?

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> ring structure w/ 8-fold symmetry
30 diff types of nuclear pore proteins (Nups)
central channel is filled w/ FG-Nups that form a selective barrier to transport

What are FG-Nups?

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Phenylatanine-glycine motifs - Nuclear pore proteins

What do NPCs have common ancestry with?

COP I, COP II & clathrin

What are the 2 types of movement through the NPC? What types of molecules are transported these ways?

Passive transport - small molecules & proteins Facilitated transport - RNAs, larger proteins, macromolecular complexes

Where does the energy for facilitated transport come from? What else does facilitated transport require?

>ATP hydrolysis for mRNA >GTP hydrolysis for proteins, tRNA & ribosomes Nuclear transport receptors = karyopherins (= karyo + phero('bring'))

What is mRNP? What does it include?

mRNA-protein complex Proteins that process, cap & splice Export factors

How is mRNP exported & imported? How does ATP hydrolysis affect mRNP?

Via the NPC Release of Dbp5 in cytoplasm & remodelling on mRNP

How are proteins imported into the nucleus?

1. Karyopherins = AKA nuclear transport receptors = AKA importins - ->bind to cargo proteins in cytoplasm 2. interact w/ FG-Nups 3. release cargos in the nucleus

How do importins release their cargo in the nucleus?

Ran-GTP binds to importin-beta --> conformational change = complex breaks apart

How are proteins exported from the nucleus?

1. Exportins bind cargo proteins in nucleus 2. interact w/ FG-Nups 3. release cargo in cytoplasm

How do exporting load their cargo in the nucleus?

Ran-GTP binds to exportin --> conformation change = complex assembly Ran-GTP then hydrolysed to Ran-GDP in cytoplasm

What are GTPases? What happens when they bind to GTP?

Molecular switches Hydrolyse a phosphate group --> forms GDP

What is GTP hydrolysis into GDP assisted by? What is GTP loading after hydrolysis assisted by?

GAP proteins in cytosol = GTPase activating proteins GEFs in nucleus = guanine nucleotide exchange factors

What are nuclear localisation signals (NLS)?

>Protein motifs approx 8 amino acids long >Can occur anywhere in protein >Many basic residues e.g. lysine, arginine, proline >Binds to importins

What are nuclear export signals (NES)?

> Sequence w/ 4 hydrophobic amino acids >e.g. LxxxLxxLxL (L= leucine, x = any other aa) > Binds to exportins

How can NLS & NES be modified?

Phosphorylation

Describe nucleocytoplasmic shuttling

1. NLS of the transcription factor NF-kB is masked when bound to IkB in cytoplasm 2. signal like cytokine (TNFa) triggers degradation of IkB 3. NF-kB can be imported to nucleus 4. NF-kB relocalises to cytoplasm via exportins binding to its NES

Which non-membrane-bound organelles are contained in the nucleus?

>Nucleoli - cells can have 1 large nucleolus or many small nucleoli >Cajal bodies >PML bodies >Speckles

What are the major functions of the nucleolus? What are their other functions?

>Transcription of rRNAs >Assembly of ribosomal subunits > sensing & responding to stress > cell cycle regulation

What is the nucleolus composed of?

> segments of 10 chromosomes encoding rRNA genes > proteins for processing rRNAs > ribosomal subunit proteins > snoRNA oligonucleotides that help process rRNAs

What are the functions of Cajal bodies? What are they made of?

RNA processing Genome organisation Dense foci of coilin protein

What are the functions of PML bodies?

DNA repair Cell proliferation Programmed cell death

What are the functions of speckles?

Gene transcription | mRNA processing

What is the role of the Ran-GTP/GDP cycle?

Maintain gradient of import/export

Nucleus Flashcards

(46 cards)