Nucleus and Nuclear Transport Flashcards
(137 cards)
1
Q
what is the largest organelle
A
nucleus
2
Q
what is nucleus size determined by
A
cell size
3
Q
do eukaryotes or prokaryotes possess a membrane bound nucleus
A
eukaryotes
4
Q
nuclear envelope
A
boundary between cytoplasm and nucleus
5
Q
nuclear pores
A
‘doorways’ in nuclear envelope that regulate transport in/out of nucleus
6
Q
nucleolus
A
site of ribosome synthesis
7
Q
nuclear matrix
A
insoluble fibrillar protein mesh/network - serves in structural support and chromatin scaffold
8
Q
nucleoplasm
A
ordered architecture - site where chromatin is found and RNA processing
9
Q
nucleoid
A
region in prokaryotes where chromosome is located
10
Q
what does a nucleoid contain less of
A
less DNA, less DNA packaging, limited/no RNA processing
11
Q
what does cellular compartmentation allow for
A
larger size and segregation and organization of specific cellular functions
12
Q
what does each organelle contain
A
unique and common factors for functions and their biogenesis, maintenance, and turnover
13
Q
what the the 2 main functions that the nucleus is responsible for
A
- compartmentalization of the cellular genome and its activities
- coordination of cellular activities
14
Q
examples of activities of the cellular genome
A
DNA replication
transcription
RNA processing
where translation components are synthesized
15
Q
examples of cellular activities in nucleus
A
control of metabolism
protein synthesis, reproduction (cell division)
16
Q
what does the separation of the cytoplasm from the genome allow for
A
unique spatial and temporal regulation of gene expression in eukaryotes
17
Q
what is the nucleoplasm
A
fluid filled interior of the nucleus - highly organized
18
Q
what does the nucleoplasm consist of
A
> 30 specialized regions/subdomains that participate in specific function
19
Q
are nuclear subdomains membrane bound
A
no
20
Q
what is the location of a gene related to
A
its activity
21
Q
where are most actively transcribed genes found
A
at periphery of chromosomal subdomains
22
Q
what are inter chromosomal channels
A
regions between chromosome subdomains that serve as barriers to prevent unwanted DNA-DNA and/or DNA-protein interactions
23
Q
where do active genes (euchromatin) from different subdomains extend into
A
inter chromosomal channels to form transcription factories
24
Q
what occurs in transcription factories
A
where transcription factors are concentrated
25
what are interchromosomal interactions
gene regulatory regions from one chromosome activate genes on another chromosome
26
what are nuclear speckles
subdomains where mRNA splicing factors concentrated
27
where are nuclear speckles often located
interchromosomal changes next to transcription factories
28
qualities of nuclear speckles
numerous and highly dynamic - often more quickly and grow/shrink and change in number depending on needs of the cell
29
where is the nuclear matrix distributed
throughout nucleoplasm
30
what is the nuclear matrix analogous to
cytoskeleton network in cytoplasm
31
what are the 3 major filament systems that the nuclear matrix is composed of
microtubules
actin microfilaments
intermediate filaments
32
what role does the nuclear matrix serve
structural - maintains overall shape of nucleus
33
how does the nuclear matrix serve as a scaffold
responsible for organizing nuclear subdomains and anchoring protein factors
34
what does the nuclear envelope separate
contents of nucleus from surrounding cytoplasm
35
what does the nuclear envelope establish
unique composition of the nucleus
36
what does the nuclear envelope spatially regulate
gene expression
37
what does the nuclear envelop produce
structural framework for nucleus
38
what are the 3 main parts that the nuclear envelope is composed of
nuclear membrane
nuclear lamia
nuclear pore complexes
39
how many membranes does the nucleus have
2 - inner and outer
40
what are the inner and outer nuclear membranes made of
phospholipid bilayers
41
what are the inner and outer membranes separated by
nuclear envelope lumen (10-50nm diameter)
42
what is the outer nuclear membrane continuous with
rough endoplasmic reticulum
43
what are ribosomes attached to
cytoplasmic surface of the outer nuclear membrane
44
what is the nuclear envelope lumen continuous with
ER lumen
45
what is unique about the inner nuclear membrane
protein composition - functionally distinct from outer membrane
46
where are the inner and outer nuclear pore complexes joined
nuclear pore complexes
47
where is the nuclear lamina located
inner surface of the nuclear inner membrane
48
what is the nuclear lamina
network of long filament like proteins
49
what does the nuclear lamina provide
mechanical support to nuclear envelope by binding to nuclear inner membrane integral proteins
50
what does the nuclear lamina serve as a scaffold for
attachment of chromatin and nuclear matrix to nuclear envelope
51
what is the nuclear pore complex (NPC)
large complex structure - channels/doorways in the nuclear envelope
52
what are ABC nuclear lamins evolutionarily related to
proteins that form intermediate filaments in cytoskeleton network
53
what is the NPC responsible for
regulated trafficking (import/export) of all substances between nucleus and cytoplasm
54
how many NPCs are there typically per nucleus
3000-4000
55
what is the number of NPCs related to
nuclear activity
56
what are nucleoporins (Nups)
proteins in the NPC
57
how many different nucleoporins are there in the NPC
40
58
overall structure of NPC
8-fold symmetrical structure organized around large, central aqueous channel
59
what is the central scaffold
part of the NPC composed of integral/trans membrane-bound nucleoporins
60
what does the central scaffold do
anchors NPC to nuclear envelope membranes (at junction of inner/outer membranes)
61
what does the central scaffold form
aqueous central channel
62
what is the central channel
20-40nm wide pore in NPC
63
what are FG nucleoporins
filament like Nups that line the inner surface of the central channel
64
what do Fg Nups possess
unusual amino acid composition
unique, highly disorders 2º structure
65
what kind of polypeptides do FG Nups possess
hydrophilic with short repeats of hydrophobic domains
66
what are FG domains
the hydrophobic domains in FG Nups enriched with phenylalanines and glycines
67
where do FG domains extend into
central channels to form a mesh that limit diffusion of macromolecules larger than 40 kDa
68
what direction do FG Nups move
freely in the NPC in either direction
69
what do Y-complexes include
cytoplasmic ring
nuclear ring
70
what are the cytoplasmic and nuclear ring in y-complexes made of
structural Nups
71
where are y-complexes located
cytoplasmic and nuclear side of NPC
72
what are y-complexes linked to
central scaffold
cytoplasmic filaments
nuclear basket
73
what are cytoplasmic filaments
long, filament shaped (structural) Nups that extend into cytoplasm
74
what are y-complexes involved in
nuclear receptor-cargo protein recognition and import from cytoplasm
75
what is the nuclear basket
basket-like structure made of structural Nups on the nuclear side of NPC
76
what are nuclear baskets linked to
y-complex ring
77
what are nuclear baskets involved in
nuclear receptor-cargo protein import and export to cytoplasm
78
what are the 2 types of nuclear localization signals (NLS)
classic and bipartite
79
what does classic NLS consist of
short stretch of positively charged (basic) amino acid residues
80
what is bipartite NLS composed of
2 short stretched of basic amino acids and 7-10 amino-acid-long spacer sequence
81
what is an NLS
an amino acid sequence that is both necessary and sufficient for cytoplasm-to-nuclear targeting
82
when is an NLS necessary for cytoplasm-to-nuclear targeting
if sequence (or portion of sequence) is mutated, modified protein fails to target to nucleus
83
when is an NLS sufficient for cytoplasm-to-nuclear targeting
if sequence linked to non-nuclear protein is capable of redirecting resulting fusion protein to nucleus
84
what is Arc1
protein required for plant pollination - shuttles between nucleus and cytoplasm
85
what are transport receptors
mobile proteins responsible for moving protein cargo across nuclear envelope
86
what are karyoferins
large family of receptor proteins responsible for moving macromolecules either into nucleus or out of nucleus
87
importins
move macromolecules into nucleus
88
exportins
move macromolecules out of nucleus
89
what does the importin alpha subunit do
recognizes and binds to basic residues in cargo protein's NLS
90
what does importin beta subunit do
binds to cytoplasmic filament at NPC
91
what is Ran
small GTP-binding protein
92
what is proteins conformation and activity regulated by
GTP binding and hydrolysis
93
what are the 2 forms of Ran
Ran-GTP
Ran-GDP
94
what form is Ran GTP
active GTP bound
95
what form is Ran GDP
inactive GDP form
96
where does a steep concentration gradient of Ran-GTP exist
between nucleus and cytoplasm
97
what does the Ran-GTO gradient determine
directionality of nucleocytoplasmic transport
98
what does the Ran-GTP gradient get mediated by
2 accessory proteins : GEF and GAP
99
what is GAP
nuclear protein that promotes conversion of Ran-GDP to Ran GTP
100
what does GEF maintain
high Ran-GTP concentration in nucleus
101
what is GAP
cytoplasmic protein that promotes hydrolysis of Ran-GTP to Ran-GDP
102
what does GAP maintain
low Ran-GTP in cytoplasm
103
what does GTP hydrolysis provide
energy required for nucleocytoplasmic transport
104
what is a nuclear export signal (NES)
specific stretch/sequence of amino acids recognized by exporting and serve as a zip code to mediate targeting protein from nucleus to cytoplasm
105
what do the most common NES consist of
leucine-rich motif
106
what is piggyback nuclear protein import
when proteins are imported into nucleus without an NLS
107
what are cyclins
nucleocytoplasmic proteins involved in the control of the cell cycle
108
what gets synthesized and degraded during each cell cycle
cyclins
109
what are the 3 stages of interphase
G1
S
G2
110
what occurs during the G1 (Gap 1) stage in interphase
cell performs normal cellular activities and can respond to environment
111
what occurs during the S (Synthesis) stage of interphase
DNA replication and increased synthesis of factors required for chromosome duplication
112
what occurs during the G2 (Gap 2) stage of interphase
cell grows and prepares for mitosis
113
what does the M phase of the cell cycle consist of
mitosis
cytokinesis
114
overall gist of mitosis
duplicated chromosomes separated into 2 nuclei
115
what occurs during cytokinesis
mother cell divides into 2 daughter cells
116
what occurs during prophase
chromosome condensation
mitotic spindle formation
reversible breakdown of nuclear envelope
117
what is progression through the cell cycle regulated by
checkpoints
118
what are the primary checkpoints in the cell cycle
mid G1
end of G2
end of metaphase
119
what occurs at the checkpoint in the middle of G1
cell commits to DNA replication in S and organelle duplication begins
120
what occurs at the checkpoint in the end of G2
cell commits to entering M phase
121
what occurs at the checkpoint at end of metaphase
cell commits to chromosome segregation
122
what is transition through checkpoints controlled by
mitotic cyclins
cyclin-dependent kinases (CDKs)
123
what are CDKs
cell-cycle-specific kinase enzymes located in nucleus
124
what do CDKs do
phosphorylate various target proteins (turn on/off)
125
what do cyclins do to CDKs
bind CDKs and regulate their activity during specific stated of cell cycle
126
when is CDK activity low
early interphase
127
when is CDK activity high
end of G2/start of M
128
what determines CDK activity
concentration of mitotic cyclins - high concentration, high CDK activity, and vice versa
129
examples of CDK target proteins in nucleus at the end of G2, start of M
histones and condensins
lamins
Nups
130
what does the phosphorylation of histones and condensins lead to
chromatin packing and chromosome condensation in prep for mitosis
131
what does the phosphorylation of lamins lead to
disassembly of nuclear lamina
132
what does the phosphorylation of Nups lead to
disassembly of NPCs
133
what is open mitosis
dynamic process in higher eukaryotes where the nucleus is completely disassembled by metaphase
134
what does a proteasome do
decrease in the concentration of mitotic cyclin after the start of M phase due to decrease synthesis of new proteins and degradation of pre-existing cyclin proteins
135
what do cytoskeleton elements serve as
highways for almost all types of intracellular transport
136
how does the cargo-importin complex move through cytoplasm
importins ability to bind cytoskeleton
137
main difference between open vs. closed mitosis
closed:
nucleus stays intact
lower eukaryotes
open:
nucleus completely disassembles by metaphase and reassembles by telophase
higher eukaryotes
