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MCB 2050 > Nucleus and Nuclear Transport > Flashcards

Nucleus and Nuclear Transport Flashcards

1
Q

what is the largest organelle

A

nucleus

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2
Q

what is nucleus size determined by

A

cell size

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3
Q

do eukaryotes or prokaryotes possess a membrane bound nucleus

A

eukaryotes

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4
Q

nuclear envelope

A

boundary between cytoplasm and nucleus

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5
Q

nuclear pores

A

‘doorways’ in nuclear envelope that regulate transport in/out of nucleus

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6
Q

nucleolus

A

site of ribosome synthesis

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7
Q

nuclear matrix

A

insoluble fibrillar protein mesh/network - serves in structural support and chromatin scaffold

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8
Q

nucleoplasm

A

ordered architecture - site where chromatin is found and RNA processing

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9
Q

nucleoid

A

region in prokaryotes where chromosome is located

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10
Q

what does a nucleoid contain less of

A

less DNA, less DNA packaging, limited/no RNA processing

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11
Q

what does cellular compartmentation allow for

A

larger size and segregation and organization of specific cellular functions

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12
Q

what does each organelle contain

A

unique and common factors for functions and their biogenesis, maintenance, and turnover

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13
Q

what the the 2 main functions that the nucleus is responsible for

A
  1. compartmentalization of the cellular genome and its activities
  2. coordination of cellular activities
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14
Q

examples of activities of the cellular genome

A

DNA replication
transcription
RNA processing
where translation components are synthesized

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15
Q

examples of cellular activities in nucleus

A

control of metabolism
protein synthesis, reproduction (cell division)

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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

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17
Q

what is the nucleoplasm

A

fluid filled interior of the nucleus - highly organized

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18
Q

what does the nucleoplasm consist of

A

> 30 specialized regions/subdomains that participate in specific function

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19
Q

are nuclear subdomains membrane bound

A

no

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20
Q

what is the location of a gene related to

A

its activity

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21
Q

where are most actively transcribed genes found

A

at periphery of chromosomal subdomains

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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

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23
Q

where do active genes (euchromatin) from different subdomains extend into

A

inter chromosomal channels to form transcription factories

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24
Q

what occurs in transcription factories

A

where transcription factors are concentrated

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25
Q

what are interchromosomal interactions

A

gene regulatory regions from one chromosome activate genes on another chromosome

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26
Q

what are nuclear speckles

A

subdomains where mRNA splicing factors concentrated

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27
Q

where are nuclear speckles often located

A

interchromosomal changes next to transcription factories

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28
Q

qualities of nuclear speckles

A

numerous and highly dynamic - often more quickly and grow/shrink and change in number depending on needs of the cell

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29
Q

where is the nuclear matrix distributed

A

throughout nucleoplasm

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30
Q

what is the nuclear matrix analogous to

A

cytoskeleton network in cytoplasm

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31
Q

what are the 3 major filament systems that the nuclear matrix is composed of

A

microtubules
actin microfilaments
intermediate filaments

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32
Q

what role does the nuclear matrix serve

A

structural - maintains overall shape of nucleus

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33
Q

how does the nuclear matrix serve as a scaffold

A

responsible for organizing nuclear subdomains and anchoring protein factors

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34
Q

what does the nuclear envelope separate

A

contents of nucleus from surrounding cytoplasm

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35
Q

what does the nuclear envelope establish

A

unique composition of the nucleus

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36
Q

what does the nuclear envelope spatially regulate

A

gene expression

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37
Q

what does the nuclear envelop produce

A

structural framework for nucleus

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38
Q

what are the 3 main parts that the nuclear envelope is composed of

A

nuclear membrane
nuclear lamia
nuclear pore complexes

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39
Q

how many membranes does the nucleus have

A

2 - inner and outer

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40
Q

what are the inner and outer nuclear membranes made of

A

phospholipid bilayers

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41
Q

what are the inner and outer membranes separated by

A

nuclear envelope lumen (10-50nm diameter)

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42
Q

what is the outer nuclear membrane continuous with

A

rough endoplasmic reticulum

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43
Q

what are ribosomes attached to

A

cytoplasmic surface of the outer nuclear membrane

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44
Q

what is the nuclear envelope lumen continuous with

A

ER lumen

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45
Q

what is unique about the inner nuclear membrane

A

protein composition - functionally distinct from outer membrane

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46
Q

where are the inner and outer nuclear pore complexes joined

A

nuclear pore complexes

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47
Q

where is the nuclear lamina located

A

inner surface of the nuclear inner membrane

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48
Q

what is the nuclear lamina

A

network of long filament like proteins

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49
Q

what does the nuclear lamina provide

A

mechanical support to nuclear envelope by binding to nuclear inner membrane integral proteins

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50
Q

what does the nuclear lamina serve as a scaffold for

A

attachment of chromatin and nuclear matrix to nuclear envelope

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51
Q

what is the nuclear pore complex (NPC)

A

large complex structure - channels/doorways in the nuclear envelope

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52
Q

what are ABC nuclear lamins evolutionarily related to

A

proteins that form intermediate filaments in cytoskeleton network

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53
Q

what is the NPC responsible for

A

regulated trafficking (import/export) of all substances between nucleus and cytoplasm

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54
Q

how many NPCs are there typically per nucleus

A

3000-4000

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55
Q

what is the number of NPCs related to

A

nuclear activity

56
Q

what are nucleoporins (Nups)

A

proteins in the NPC

57
Q

how many different nucleoporins are there in the NPC

A

40

58
Q

overall structure of NPC

A

8-fold symmetrical structure organized around large, central aqueous channel

59
Q

what is the central scaffold

A

part of the NPC composed of integral/trans membrane-bound nucleoporins

60
Q

what does the central scaffold do

A

anchors NPC to nuclear envelope membranes (at junction of inner/outer membranes)

61
Q

what does the central scaffold form

A

aqueous central channel

62
Q

what is the central channel

A

20-40nm wide pore in NPC

63
Q

what are FG nucleoporins

A

filament like Nups that line the inner surface of the central channel

64
Q

what do Fg Nups possess

A

unusual amino acid composition
unique, highly disorders 2º structure

65
Q

what kind of polypeptides do FG Nups possess

A

hydrophilic with short repeats of hydrophobic domains

66
Q

what are FG domains

A

the hydrophobic domains in FG Nups enriched with phenylalanines and glycines

67
Q

where do FG domains extend into

A

central channels to form a mesh that limit diffusion of macromolecules larger than 40 kDa

68
Q

what direction do FG Nups move

A

freely in the NPC in either direction

69
Q

what do Y-complexes include

A

cytoplasmic ring
nuclear ring

70
Q

what are the cytoplasmic and nuclear ring in y-complexes made of

A

structural Nups

71
Q

where are y-complexes located

A

cytoplasmic and nuclear side of NPC

72
Q

what are y-complexes linked to

A

central scaffold
cytoplasmic filaments
nuclear basket

73
Q

what are cytoplasmic filaments

A

long, filament shaped (structural) Nups that extend into cytoplasm

74
Q

what are y-complexes involved in

A

nuclear receptor-cargo protein recognition and import from cytoplasm

75
Q

what is the nuclear basket

A

basket-like structure made of structural Nups on the nuclear side of NPC

76
Q

what are nuclear baskets linked to

A

y-complex ring

77
Q

what are nuclear baskets involved in

A

nuclear receptor-cargo protein import and export to cytoplasm

78
Q

what are the 2 types of nuclear localization signals (NLS)

A

classic and bipartite

79
Q

what does classic NLS consist of

A

short stretch of positively charged (basic) amino acid residues

80
Q

what is bipartite NLS composed of

A

2 short stretched of basic amino acids and 7-10 amino-acid-long spacer sequence

81
Q

what is an NLS

A

an amino acid sequence that is both necessary and sufficient for cytoplasm-to-nuclear targeting

82
Q

when is an NLS necessary for cytoplasm-to-nuclear targeting

A

if sequence (or portion of sequence) is mutated, modified protein fails to target to nucleus

83
Q

when is an NLS sufficient for cytoplasm-to-nuclear targeting

A

if sequence linked to non-nuclear protein is capable of redirecting resulting fusion protein to nucleus

84
Q

what is Arc1

A

protein required for plant pollination - shuttles between nucleus and cytoplasm

85
Q

what are transport receptors

A

mobile proteins responsible for moving protein cargo across nuclear envelope

86
Q

what are karyoferins

A

large family of receptor proteins responsible for moving macromolecules either into nucleus or out of nucleus

87
Q

importins

A

move macromolecules into nucleus

88
Q

exportins

A

move macromolecules out of nucleus

89
Q

what does the importin alpha subunit do

A

recognizes and binds to basic residues in cargo protein’s NLS

90
Q

what does importin beta subunit do

A

binds to cytoplasmic filament at NPC

91
Q

what is Ran

A

small GTP-binding protein

92
Q

what is proteins conformation and activity regulated by

A

GTP binding and hydrolysis

93
Q

what are the 2 forms of Ran

A

Ran-GTP
Ran-GDP

94
Q

what form is Ran GTP

A

active GTP bound

95
Q

what form is Ran GDP

A

inactive GDP form

96
Q

where does a steep concentration gradient of Ran-GTP exist

A

between nucleus and cytoplasm

97
Q

what does the Ran-GTO gradient determine

A

directionality of nucleocytoplasmic transport

98
Q

what does the Ran-GTP gradient get mediated by

A

2 accessory proteins : GEF and GAP

99
Q

what is GAP

A

nuclear protein that promotes conversion of Ran-GDP to Ran GTP

100
Q

what does GEF maintain

A

high Ran-GTP concentration in nucleus

101
Q

what is GAP

A

cytoplasmic protein that promotes hydrolysis of Ran-GTP to Ran-GDP

102
Q

what does GAP maintain

A

low Ran-GTP in cytoplasm

103
Q

what does GTP hydrolysis provide

A

energy required for nucleocytoplasmic transport

104
Q

what is a nuclear export signal (NES)

A

specific stretch/sequence of amino acids recognized by exporting and serve as a zip code to mediate targeting protein from nucleus to cytoplasm

105
Q

what do the most common NES consist of

A

leucine-rich motif

106
Q

what is piggyback nuclear protein import

A

when proteins are imported into nucleus without an NLS

107
Q

what are cyclins

A

nucleocytoplasmic proteins involved in the control of the cell cycle

108
Q

what gets synthesized and degraded during each cell cycle

A

cyclins

109
Q

what are the 3 stages of interphase

A

G1
S
G2

110
Q

what occurs during the G1 (Gap 1) stage in interphase

A

cell performs normal cellular activities and can respond to environment

111
Q

what occurs during the S (Synthesis) stage of interphase

A

DNA replication and increased synthesis of factors required for chromosome duplication

112
Q

what occurs during the G2 (Gap 2) stage of interphase

A

cell grows and prepares for mitosis

113
Q

what does the M phase of the cell cycle consist of

A

mitosis
cytokinesis

114
Q

overall gist of mitosis

A

duplicated chromosomes separated into 2 nuclei

115
Q

what occurs during cytokinesis

A

mother cell divides into 2 daughter cells

116
Q

what occurs during prophase

A

chromosome condensation
mitotic spindle formation
reversible breakdown of nuclear envelope

117
Q

what is progression through the cell cycle regulated by

A

checkpoints

118
Q

what are the primary checkpoints in the cell cycle

A

mid G1
end of G2
end of metaphase

119
Q

what occurs at the checkpoint in the middle of G1

A

cell commits to DNA replication in S and organelle duplication begins

120
Q

what occurs at the checkpoint in the end of G2

A

cell commits to entering M phase

121
Q

what occurs at the checkpoint at end of metaphase

A

cell commits to chromosome segregation

122
Q

what is transition through checkpoints controlled by

A

mitotic cyclins
cyclin-dependent kinases (CDKs)

123
Q

what are CDKs

A

cell-cycle-specific kinase enzymes located in nucleus

124
Q

what do CDKs do

A

phosphorylate various target proteins (turn on/off)

125
Q

what do cyclins do to CDKs

A

bind CDKs and regulate their activity during specific stated of cell cycle

126
Q

when is CDK activity low

A

early interphase

127
Q

when is CDK activity high

A

end of G2/start of M

128
Q

what determines CDK activity

A

concentration of mitotic cyclins - high concentration, high CDK activity, and vice versa

129
Q

examples of CDK target proteins in nucleus at the end of G2, start of M

A

histones and condensins
lamins
Nups

130
Q

what does the phosphorylation of histones and condensins lead to

A

chromatin packing and chromosome condensation in prep for mitosis

131
Q

what does the phosphorylation of lamins lead to

A

disassembly of nuclear lamina

132
Q

what does the phosphorylation of Nups lead to

A

disassembly of NPCs

133
Q

what is open mitosis

A

dynamic process in higher eukaryotes where the nucleus is completely disassembled by metaphase

134
Q

what does a proteasome do

A

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
Q

what do cytoskeleton elements serve as

A

highways for almost all types of intracellular transport

136
Q

how does the cargo-importin complex move through cytoplasm

A

importins ability to bind cytoskeleton

137
Q

main difference between open vs. closed mitosis

A

closed:
nucleus stays intact
lower eukaryotes
open:
nucleus completely disassembles by metaphase and reassembles by telophase
higher eukaryotes

MCB 2050 (11 decks)

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