Chapter 10 Flashcards
________________: separates the nuclear contents from the cytoplasm
it controls traffic of ___________ through nuclear pore complexes, and plays a critical role in regulating gene expression
the nuclear envelope consists of 1) _______________2) and underlying____________ 3)____________. outer membrane is continuous with the ________________. Inner membrane has proteins that bind the nuclear ___________-
NUCLEAR ENVELOPE: separates the nuclear contents from the cytoplasm. It controls traffic of PROTEINS AND RNAs through nuclear pore complexes, and plays a critical role in regulating gene expression
The nuclear envelope consists of 1)two NUCLEAR MEMBRANE, 2) an underlying NUCLEAR LAMINA, 3) NUCLEAR PORE COMPLEX. Outer membrane is continuous with the ENDOPLASMIC RECTICULUM. inner membrane has proteins that bind the nuclear LAMINA
nuclear membrane are ____________ permeable only to _________________________-
phospholipid bilayers.
small nonpolar molecules
nuclear pore complexes are only channels for _____________,__________ and __________-
small polar molecules, ions, and macromolecules
______________________ : a fibrous mesh that provides structural support
consists of fibrous proteins (________) and other proteins
nuclear lamina
lamins
lamins are a class of intermediate filament proteins that associate to form higher order structures.
___________ interact to form a dimer: the alpha-helical regions wind around each other to form a coiled coil. the lamin dimers associate with each other to form the lamina
two lamins
mutations in lamin genes cause several inherited tissue-specific diseases. The bases of the pathologies in each of these disease is unclear _______________
hutchinson gliford progeria
lamins bind to inner __________ such as emerin and lamin B receptor (LBR)
the y are connected to the cytoskeleton by LINC protein complexes
lamins also bind to _________
inner MEMBRANE PROTEINS
TO CHROMATIN
_______________ are composed of about 30 different pore proteins (nucleoporins)
- RNAs synthesized in the nucleus must be exported to the cytoplasm for protein synthesis
- proteins needed for nuclear functions must be imported from synthesis sites in the cytoplasm
- molecules pass through pore complexes by two mechanisms
- __________________- small molecules pass freely in either direction
- __________________-are selectively transported ;requires energy
NUCLEAR PORE COMPLEXES= are composed of about 30 different pore proteins (nucleoporins)
PASSIVE DIFFUSION
PROTEINS AND RNA
electron microscopy shows pore complexes have _______ subunits organized around a large central channel
8 subunits
_________________ are connected to rings at the nuclear and cytoplasmic surfaces
the ____________ surrounds a ____________.
protein filaments extend from the rings, forming a basketlike structure on the nuclear side
the SPOKE RING ASSEMBLY surrounds a CENTRAL CHANNEL
proteins that must enter the nucleus have amino acid sequences called ________________-
these signals are recognized by _______________
nuclear localization signals were first identified in 1984, using a viral replication protein SV40T antien
the amino acid sequence is responsible for nuclear localization was determined using T antigen mutants.
when the same sequence was attached to other proteins, they were also transported to the nucleus
nuclear localization signals
nuclear transport
the ________ nuclear localization signal is a signal stretch of amino acids
others are ___________ consisting of two amino acids sequences separated by another amino acid sequences
T antigens
bipartite (nucleopasmin)
nuclear localization signals (NLS) are recognized by receptors called _____________, which carry proteins through the nuclear pore complex
importins work in conjuction with the GTP-binding protein __________, which controls directionality of movement
importins bind to the __________ of a protein, then to nuclear pore proteins and the complex is transported across the membrane
importins
ran
NLS of a protein
Ran/GTP binds to the importin, and this complex is transported by into tthe cytoplasm. Ran GAP hydrolyzes the GTP on Ran to GDP, releasing the importin. The Ran/GDP formed in the cytoplasm is then transported back to the nucleus by its own import receptor, where Ran/GTP is regenerated
General informaiton
protiens export from the nucleus:
proteins are targeted for export by amino acid sequences called _______________________-
NES are recognized by receptors in the nucleaus (_______), which direct protein transport to the cytoplasm
export signals (NES)
exportins
many importins and exportins are members of _______ known as _____________________
are members of A FMAILY OF NUCLEAR TRANSPORT RECEPTORS and KARYOPHERINS
General information:
exportins form stable complexes with cargo proteins in association with Ran/GTP in the nucleus
in the cytoplasm, GTP hydrolysis and release of Ran/GDP leads to dissociation of the cargo protein
general information
RNAs are transported to the cytoplasm as ribonucleoprotein complexes (RNPs)
karyopherin exportins transport ____________, _________, _____________
tRNAs, rRNAs, miRNAs
mRNA transport does not involve karyopherins and is independent of Ran.
a distinct transporter complex moves the mRNA through the nuclear pore
_________________, on the cytoplasm side releases the mRNA and ensures unidirectional transport
helicase
“transport of snRNAs between nucleus and cytoplasm”
- many small RNAs (snRNAs and snoRNAs) function within the nucleus.
- snRNAs are exported from the nucleus by an exportin (Crm1)
- in the cytoplasm, the snRNAs associate with proteins to form snRNPs, which are recognized by an importin and transported back to the nucleus
___________________________
small nuclear ribonucleoprotein particles (snRNPs)
regulation of protein transport is a mechanism for controlling protein activity _____________________
example: regulation of import and export of transcription factors is a way of controlling gene expression
in one mechanism, transcription factors or other proteins associate with cytoplasmic proteins that mask their NLS, and so they remain in the cytplasm
transcription facotr NF-kB is complexed with lkB in the cytplasm
if IkB is phophorylated and degraded by ubiquitin-mediated proteolysis, NF0kB can enter the nucleus and activate transcription of its target genes
in the nucleus
chromatin becomes highly _____________ during mitosis to form the compct metaphase chromosomes
during inter phase, most of the chromatin ____________ and its distributed throughout the nucleus
but even in interphase, the chromosome occupy distinct regions and are organized such that transcriptional activity of a gene is correlated with its position
DNA replication and transcription first takes place in clustered regions within the nucleus
highly condensed
decondenses
eahc chromosome was found to occupy a discrete region of the nucleus called the _______________
in _______ cell nuclei, each chromosome occupies a discrete region of the nucleus
recent studies have demonstrated that individual chromosomes also occupy distinct territories in mammalian cell nuclei
chromosome territory
drosophila cell
in situ hybridization with fluorescent probes specific for repeated sequences on individual chromosomes has been used to visualize the location of chromosomes within a nucleus
general information
in interphase cell the ______________ is decondensed and transcriptionally-active, and is distributed throughout the nucleus
______________ is highly consdensed and not transcribed ,and is often associated with the ____________ or periphery of the __________
euchromatin
heterochromatin
nuclear envelope
nucleolus
some human chromosomes are rich in transcribed genes, whereas others contain relatively few genes
fluorescent in situ hybridization shows that gene-rich chromosomes are located ______ of the nucleus; and ___________ chromosmes are located at the periphery
gene-rich chromosomes are located in the CENTER of the nucleus. GENE_POOR chromosomes are at the periphery
genomes are divided into ______________________–
regions within a domain interact frequently with one another, but only rarely with regions from other domains
divided into topologically associating domains
some domains are associated with the nuclear lamina (called ____________________). the genes within Lads are generally transcriptionally repressed
lamina associated domains or LADS
the nucleollus is also surrounded by heterochromatin (called ____________) . DNA sequences found in NADs substantially overlap with those in LADs. Most nuclear processes occur in distinct regions
nucleolus-associated domains or NAD
_____________ takes place in large complexes called __________________, where replication of multiple DNA molcules take place
these can be seen by labeling cells with bromodeoxyuridine, (an analog of thymidine(, then staining with fluorescent antibodies
`DNA replication
replication factors
___________ occurs at clustered sites (_____________) that contain newly synthesized RNA
coregulated genes, such as immunoglobulin gene from different chromosomes, may be transcribed inthe same factory
transcription
transcription factors
_____________ are organelles within the nucleus that concentrate __________ for ____ for specific processes
they are not enclosed by the membrane: they are dynamic structures maintained by protein-protein and protein-RNA interactions
nuclear bodies
protiens and RNA
“nuclear bodies”
- the ______ functions in ____________ and ________. cells need large numbers of ribosomes at specific times for protein synthesis
actively growing mammal cells have 5 to 10 million ribosomes thatm ust be synthesized each time the cell divides
nucleolus rRNA synthesis ribosome production
“nuclear bodies”
- the 5.8S, 18S, and 28S rRNAs are transcribed as a single unit in the nucleolus by RNA polymerase I, yielding a 45S ribosomal precursor RNA. transcription of the 5S rRNA takes place _____________________ and is catalyzes by RNA polymerase III
outside the nucleolus
“nuclear bodies”
- following each cell division, nucleoli become associated with the ___________ that contain the ________________ genes
nucleolar organizing regions
5.8S, 18S, 28S rRNA
nucleoli have three regions
they represent sites of progressive stages of rRNA transcription, processing, and ribosome assembly
FC: gene encoding rRNA, interface of FC and DFC: trancription; DFC: Pre-RNA is processed, G: assembly of ribosomal subunits
fibrillar center
dense fibrillar component
granular component
each _____________ contains a cluster of tandemly repeated rRNA genes separted by spacer DNA
the genes are actively transcribed by RNA polymerase I, and their growing RNA chains can be seen in electron micrographs
nucleolar organizing region
in higher prokaryotes, the primary transcript of rRNA gens is the __________
the pre-rRNA is processed via a series of cleavages, which is similar in all eukaryotes
45S pre rRNA
formation of ribosomes requries assembly of ___________ with __________ and ______
__________ are produced in the cytoplasm and imported to the nucleolus, where they assemble with the pre-rRNA prior to cleavage
5S rRNAs are produced elsewhere in the nucleolus
additional ribosomal proteins and the 5S rRNA assmemble to form pre ribosomal particles
pre-ribosomal particles are then exported to the cytoplasm, yeilding the 40S and 60S ribosomal subunits
formation of ribosomes requires assembly of PRE-rRNA with RIBOSOMAL PROTEINS, and 5S rRNA
RIBOSOMAL PROTEINS are produced in the cytoplasm and imported to the nucleus, where they assemble with the pre-rRNA prior to cleavage
_______________ are involved in the assembly of snRNPs and other RNA-protein complexes
snRNAs are modified by ribose methylation and pseudouridylation. the enzyme for RNA methylation (fibrillarin) is concentrated in Cajal bodies
cajal bodies
following assembly and maturation in cajal bodies, snRNPs are transferred to _______, which also contain splicing factors
speckles
speckles are recruited to actively transcribed genes where ________________ processing occurs
pre-mRNA
