Chapter 11: The Nucleus Flashcards by Yessenia Palacio

what NEVER transects the inner membrane of the nucleus?

the perinuclear space

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list the 7 components of the nuclear envelope complex

nucleoplasm
perinuclear space
nuclear lamina
nuclear pore complex
IM
OM
endoplasmic reticulum

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describe the nucleolus

a dense concentrated bundle of DNA where ribosomes are made

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list 5 functions of the nuclear envelope

structure
barrier
OM contains ribosomes
connection w/ lumen of ER
IM carries nucleus specific proteins

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define lamins

fibrous proteins that compose the nuclear lamina

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what structures are included in the nuclear lamina

lamin filaments
nuclear pores
LBR
Emerin
chromatin

LBR: lamin B receptor

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where is the nuclear lamina found?

under the IM

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how many types of lamins are in mammalian cells? list them.

4 types

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lamins can associate w/ the…

inner nuclear membrane and chromatin

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what is the name for diseases caused by deficiencies of lamins?

laminopathies

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nuclear pore complexes are channels through which…

molecules cross the nuclear membrane

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transport across the channels of nuclear pores is said to be

selective

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FG-NUPs are

protein complexes embedded in the channel of nuclear pores

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FG- NUPs are mainly composed of

phenylalanine

glycine

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nuclear pores are __________ in the nucleus memebrane?

embedded

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what type of symmetry is expressed by nuclear pores?

8-spoke symmetry

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give examples of what passes through nuclear pores.

RNAs
proteins
ribosomes
ions
transcription factors

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How does the cell know which proteins to transport into the nucleus?

with nuclear localization signals (NLS)

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what are NLSs?

specific amino acid sequences that target proteins to the nucleus

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NLSs are typically rich in what amino acids?

basic amino acids
- lysine & arginine

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signal sequences can be located anywhere in the protein but NLSs are specifically located _________ in the protein

intrinsically

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why is the location of NLSs important?

they can not be removed
allow nucleus specific proteins to return to the nucleus after nuclear envelope dissociation and reassociation

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what is the function of importins?

to carry proteins into the nucleus

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importins recognize..

NLSs

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importins work in conjunction w/

Ran

Ran is a

GTP binding protein

what are known as the off/on switches of nuclear transport?

G proteins

give 2 examples of G proteins

- GTP - GDP

what is the function of Ran-GTP?

to hydrolyze Ran-GTP into Ran- GDP

what is the function of Ran-GEF?

to exchange the GDP for GTP resulting in Ran-GTP

where does Ran-GTP's activity occur?

in the cytoplasm

where does Ran-GEF's activity occur?

in the nucleus

define karyopherins

molecules that are responsible for the transport of compounds in and out of the cell

name two types of karyopherins

- importins - exportins

what are the 2 methods of regulation of nuclear transport?

1. NF-κB 2. Pho4

NF-κB is maintained inactive by

inhibitory proteins

Pho4 is maintained inactive through

phosphorylation

How is NF-κB activated?

by phosphorylation and proteolysis of IκB | - done according to extracellular signals

How is Pho4 activated?

by dephosphorylation exposing NLS

the nucleolus is the site of...

rRNA transcription and ribosomal assembly

define heterochromatin

condensed chromatin

is heterochromatin transcribed?

define euchromatin

chromatin in interphase

is euchromatin transcriptionally active?

YES

chromosomes in the nucleus are organized into

discrete functional domains

in what ways can chromosomes be organized?

- by polarity - into territories

where are centromeres and telomers found when the chromosomes are organized by polarity?

at opposite ends of the nucleus

where are transcribed genes locate in the chromosomal territories?

to the periphery | - outer limits 'edge'

where are gene rich chromosomes located?

at the center of the nucleus

where are gene poor chromosomes located?

in the outer limits of the nucleus

what does the outward extension of chromosomes suggest?

that transcribed genes loop out to facilitate transcription

inactive chromosomes associate w/

the lamina or the nucleolus

what is the function of cohesin

to form domain boundaries of transcriptionally active portions

what are replication factories

discrete clustering of chromatin for efficient transcription

what are transcription factories

clustered sites of newly synthesized RNA for efficient gene expression

transcription factories are highly enriched in

- new mRNAs - RNA polymerases - transcription factors

what is the most prominent nuclear substructure?

the nucleolus

the nucleolus is the site of

- rRNA processing - ribosome assembly

what are the 3 distinct regions of the nucleoli?

1. fibrillar center 2. dense fibrillar component 3. granular component

the fibrillar center is the location of genes encoding for

rRNA

the fibrillar center is the location of

RNA transcription

where is rRNA transcribed?

at the interface of the fibrillar compartment the dense fibrillar component

the dense fibrillar component is the location of

pre-rRNA processing

the granular component is the location of

pre-ribosome assembly

what genes are called nucleolar organizing regions?

the genes that contain rRNA genes

list the 4 nuclear bodies

1. cajal bodies 2. polycomb bodies 3. PML bodies 4. speckles

cajal bodies are involved w/ the assembly of...

- snRNPs - RNA complexes (telomerase)

cajal bodies are the location of

snRNPs maturation

cajal bodies are enriched w/

- fibrillarin - coilin

fibrillarin is responsible for

RNA methylation

nuclear speckles are storage sites for

RNA splicing components

nuclear speckles are active sites of

pre-mRNA splicing

nuclear speckles receive _________ from cajal bodies

snRNPs

PML bodies use transcription factors to

induce differentiation

PML bodies are found fragmentated in cells from

acute promyelocytic leukemia

polycomb bodies are sites of

gene silencing

what method is used for gene repression in polycomb bodies

histone methylation

what type of chromatin are polycomb bodies likely to associate with

heterochromatin

after cell division how does the nucleolus reform?

by fusing individual nucleoli that have previously formed around chromosomes containing rRNA genes

describe the steps in the dissociation of the nuclear envelope

1. Cdk1 phosphorylates lamins creating lamin dimers 2. nuclear membrane vesicles w/ lamin Bs form

which lamins roam freely when the nuclear envelope dissociates?

lamins A &C

describe the steps in the reformation of the nuclear envelope

1. Cdk1 gets deactivated 2. lamins are dephosphorylated 3. vesicles bind to daughter chromosomes 4. vesicles fuse around chromosomes 5. individual vesicles fuse together 6. nuclear lamina & pores reform