Chapter 11: The Nucleus Flashcards
what NEVER transects the inner membrane of the nucleus?
the perinuclear space
list the 7 components of the nuclear envelope complex
- nucleoplasm
- perinuclear space
- nuclear lamina
- nuclear pore complex
- IM
- OM
- endoplasmic reticulum
describe the nucleolus
a dense concentrated bundle of DNA where ribosomes are made
list 5 functions of the nuclear envelope
- structure
- barrier
- OM contains ribosomes
- connection w/ lumen of ER
- IM carries nucleus specific proteins
define lamins
fibrous proteins that compose the nuclear lamina
what structures are included in the nuclear lamina
- lamin filaments
- nuclear pores
- LBR
- Emerin
- chromatin
LBR: lamin B receptor
where is the nuclear lamina found?
under the IM
how many types of lamins are in mammalian cells? list them.
4 types
- A
- B1
- B2
- C
lamins can associate w/ the…
inner nuclear membrane and chromatin
what is the name for diseases caused by deficiencies of lamins?
laminopathies
nuclear pore complexes are channels through which…
molecules cross the nuclear membrane
transport across the channels of nuclear pores is said to be
selective
FG-NUPs are
protein complexes embedded in the channel of nuclear pores
FG- NUPs are mainly composed of
phenylalanine
glycine
nuclear pores are __________ in the nucleus memebrane?
embedded
what type of symmetry is expressed by nuclear pores?
8-spoke symmetry
give examples of what passes through nuclear pores.
- RNAs
- proteins
- ribosomes
- ions
- transcription factors
How does the cell know which proteins to transport into the nucleus?
with nuclear localization signals (NLS)
what are NLSs?
specific amino acid sequences that target proteins to the nucleus
NLSs are typically rich in what amino acids?
basic amino acids
- lysine & arginine
signal sequences can be located anywhere in the protein but NLSs are specifically located _________ in the protein
intrinsically
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
what is the function of importins?
to carry proteins into the nucleus
importins recognize..
NLSs
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?
- NF-κB
- 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?
NO
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?
- fibrillar center
- dense fibrillar component
- 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
- cajal bodies
- polycomb bodies
- PML bodies
- 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
- Cdk1 phosphorylates lamins creating lamin dimers
- 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
- Cdk1 gets deactivated
- lamins are dephosphorylated
- vesicles bind to daughter chromosomes
- vesicles fuse around chromosomes
- individual vesicles fuse together
- nuclear lamina & pores reform
