Chapter 10

Question 1

________________: 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 ___________-

Answer 1

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

Question 2

nuclear membrane are ____________ permeable only to _________________________-

Answer 2

phospholipid bilayers.

small nonpolar molecules

Question 3

nuclear pore complexes are only channels for _____________,__________ and __________-

Answer 3

small polar molecules, ions, and macromolecules

Question 4

______________________ : a fibrous mesh that provides structural support

consists of fibrous proteins (________) and other proteins

Answer 4

nuclear lamina

lamins

Question 5

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

Answer 5

two lamins

Question 6

mutations in lamin genes cause several inherited tissue-specific diseases. The bases of the pathologies in each of these disease is unclear _______________

Answer 6

hutchinson gliford progeria

Question 7

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 _________

Answer 7

inner MEMBRANE PROTEINS

TO CHROMATIN

Question 8

_______________ are composed of about 30 different pore proteins (nucleoporins)

1. RNAs synthesized in the nucleus must be exported to the cytoplasm for protein synthesis
2. proteins needed for nuclear functions must be imported from synthesis sites in the cytoplasm
3. molecules pass through pore complexes by two mechanisms

• __________________- small molecules pass freely in either direction
• __________________-are selectively transported ;requires energy

Answer 8

NUCLEAR PORE COMPLEXES= are composed of about 30 different pore proteins (nucleoporins)

PASSIVE DIFFUSION

PROTEINS AND RNA

Question 9

electron microscopy shows pore complexes have _______ subunits organized around a large central channel

Answer 9

8 subunits

Question 10

_________________ 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

Answer 10

the SPOKE RING ASSEMBLY surrounds a CENTRAL CHANNEL

Question 11

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

Answer 11

nuclear localization signals

nuclear transport

Question 12

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

Answer 12

T antigens

bipartite (nucleopasmin)

Question 13

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

Answer 13

importins

ran

NLS of a protein

Question 14

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

Answer 14

General informaiton

Question 15

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

Answer 15

export signals (NES)

exportins

Question 16

many importins and exportins are members of _______ known as _____________________

Answer 16

are members of A FMAILY OF NUCLEAR TRANSPORT RECEPTORS and KARYOPHERINS

Question 17

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

Answer 17

general information

Question 18

RNAs are transported to the cytoplasm as ribonucleoprotein complexes (RNPs)

karyopherin exportins transport ____________, _________, _____________

Answer 18

tRNAs, rRNAs, miRNAs

Question 19

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

Answer 19

helicase

Question 20

“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

___________________________

Answer 20

small nuclear ribonucleoprotein particles (snRNPs)

Question 21

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

Answer 21

in the nucleus

Question 22

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

Answer 22

highly condensed

decondenses

Question 23

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

Answer 23

chromosome territory

drosophila cell

Question 24

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

Answer 24

general information

Question 25

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 __________

Answer 25

euchromatin

heterochromatin

nuclear envelope

nucleolus

Question 26

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

Answer 26

gene-rich chromosomes are located in the CENTER of the nucleus. GENE_POOR chromosomes are at the periphery

Question 27

genomes are divided into ______________________–

regions within a domain interact frequently with one another, but only rarely with regions from other domains

Answer 27

divided into topologically associating domains

Question 28

some domains are associated with the nuclear lamina (called ____________________). the genes within Lads are generally transcriptionally repressed

Answer 28

lamina associated domains or LADS

Question 29

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

Answer 29

nucleolus-associated domains or NAD

Question 30

_____________ 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

Answer 30

`DNA replication

replication factors

Question 31

___________ occurs at clustered sites (_____________) that contain newly synthesized RNA

coregulated genes, such as immunoglobulin gene from different chromosomes, may be transcribed inthe same factory

Answer 31

transcription

transcription factors

Question 32

_____________ 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

Answer 32

nuclear bodies

protiens and RNA

Question 33

“nuclear bodies”

1. 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

Answer 33

nucleolus rRNA synthesis ribosome production

Question 34

“nuclear bodies”

2. 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

Answer 34

outside the nucleolus

Question 35

“nuclear bodies”

3. following each cell division, nucleoli become associated with the ___________ that contain the ________________ genes

Answer 35

nucleolar organizing regions

5.8S, 18S, 28S rRNA

Question 36

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

Answer 36

fibrillar center

dense fibrillar component

granular component

Question 37

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

Answer 37

nucleolar organizing region

Question 38

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

Answer 38

45S pre rRNA

Question 39

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

Answer 39

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

Question 40

_______________ 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

Answer 40

cajal bodies

Question 41

following assembly and maturation in cajal bodies, snRNPs are transferred to _______, which also contain splicing factors

Answer 41

speckles

Question 42

speckles are recruited to actively transcribed genes where ________________ processing occurs

Answer 42

pre-mRNA