Cell Bio exam 4

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for what are cells dependent on the cytoskeleton?

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Biology

Cells

215 Terms

1

for what are cells dependent on the cytoskeleton?

organization, shape, environment interaction, movement

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2

how does the cytoskeleton differ in eukaryotic and prokaryotic cells?

prominent in eukaryotic, in prokaryotic but not complex

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3

what are the three cytoskeletal elements?

intermediate filaments, microtubules, actin filaments

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4

describe intermediate filaments:

  • in smooth muscle cells

  • named due to size

  • prevents cells from shearing apart

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5

where are intermediate filaments prominent?

in the cytoplasm of cells that are subject to mechanical stress

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6

what are the key properties of intermediate filaments?

great strength, extreme durability

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7

what does the great strength of intermediate filaments enable cells to do?

withstand the mechanical stress that occurs when cells are stretched

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8

what does the durability of intermediate filaments allow them to withstand?

a solution of concentrated salts and detergents

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9

what do intermediate filaments typically form?

network through the cytoplasm

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10

what do desmosomes anchor?

intermediate filaments to the plasma membrane

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11

what are the benefits of intermediate filaments found inside the nucleus?

strengthens the nuclear envelope, aids cell cycle regulation

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12

what are lamins?

specialized intermediate filaments

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13

what are the functions of the nuclear lamina?

nuclear membrane support, regulation of cell division

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14

what is the nuclear lamina controlled by?

protein phosphorylation of the lamins

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15

what is the function of protein kinase?

weakens the interactions between the lamin tetramers

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16

what is the function of protein phosphatase?

removes phosphate and promotes reassembly

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17

why is the nuclear lamina targeted in cancer therapies?

prevents disassembly or reassembly, causes apoptosis

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18

what is the function of accessory proteins?

cross links filaments into bundles and connects them to various structures, binds to chromosomes and nuclear lamina

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19

you add a drug to a community of cells that are undergoing mitosis. this drug inhibits activity of the enzyme that phosphorylates nuclear lamina. what do you predict will happen?

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20

what is progeria?

rare disorder that causes individuals to age prematurely

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21

what is progeria caused by?

mutation in the LMNA gene and defect in nuclear lamin

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22

what are microtubules?

long and relatively stiff hollow tubes composed of tubulin dimers

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23

for what functions are microtubules crucial?

cell shape, cell locomotion, intracellular organelle transport, separation of chromosomes during mitosis

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24

what are protofilaments?

dimers stacked together, have structural polarity

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25

what does the centrosome consist of?

a pair of centrioles surrounded by a protein matrix

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26

what does the protein matrix serve as?

a nucleation site (starting part) for the growth of one microtubule

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27

describe the dynamic instability of microtubules:

fluctuate every few minutes between growing and shrinking

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28

how do microtubules become stabilized?

the plus end binding to an accessory protein

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29

what does dynamic instability stem from?

intrinsic capacity of tubulin dimers to hydrolyze GTP

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30

what is the rate of tubulin dimer addition relative to?

the rate of GTP hydrolysis

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31

when do microtubules have a GTP cap?

when GTP bound tubulin dimers are added more rapidly than GTP hydrolysis

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32

what happens to GTP if the rate of polymerization slows?

it will hydrolyze to GDP, causing the GDP tubulin to dissociate

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33

your cells are artificially supplied with nonhydrolyzable GTP. what effect would this have on microtubules?

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34

how do microtubules influence mitosis?

their dynamic nature allows for mitotic spindle formation

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35

how do cells utilize dynamic instability for differentiation?

it is suppressed by proteins that bind to microtubules and protect against disassembly

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36

what is taxol?

cancer drug derived from pacific yew trees

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37

how does taxol modify microtubule dynamics?

  • prevents tubulin loss

  • prevents mitotic spindle from shortening during anaphase

  • arrests cells in mitosis, triggering apoptosis

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38

what are microtubule "roadways" utilized for?

moving transport vesicles and organelles

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39

what is movement controlled by?

motor proteins

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40

what are the most abundant cytoskeletal proteins of MOST cells?

actin filaments

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41

what cell movements are actin filaments essential for?

mechanical support, cell shape, movement of the cell surface

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42

what are actin monomers bound to?

ATP

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43

is ATP an energy source?

NO

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44

what does the hydrolyzation of ATP to ADP cause?

  • decrease in stability of the monomer in the actin filament

  • dissociation of filament at its end

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45

what does treadmilling refer to?

the process of adding monomers to the (+) end and removing monomers from (-) end

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46

what does treadmilling dictate?

the size of the actin filament

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47

what do actin-binding proteins control?

location, organization, and behavior of actin filaments

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48

in the budding yeast, activation of the GTP-binding protein Cdc42 occurs on binding of an external signal to a GPCR, promoting actin polymerization. what would happen if you added a toxin that binds to the GPCR?

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49

what occurs simultaneously with protein sorting?

phospholipid synthesis/sorting

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50

where does most protein synthesis begin?

ribosomes in the cytosol

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51

what is the exception to location of protein synthesis?

few mitochondria and chloroplast proteins are synthesized by ribosomes inside the organelle

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52

what does the fate of any protein synthesized in the cytosol depend on?

amino acid sequence (sorting signal)

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53

what is the fate of proteins which lack a sorting signal?

remain permanently in the cytosol

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54

what is the sorting signal?

sequence of 3-60 amino acids, often removed after protein is sorted

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55

what are the two concentric membranes which form the nuclear envelope?

inner nuclear membrane, outer nuclear membrane

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56

describe the inner nuclear membrane:

  • contains proteins which act as binding sites for chromosomes

  • provides anchorage for the nuclear lamina

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57

describe the outer nuclear membrane:

  • similar to the membrane of the ER

  • continuous with ER

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58

what are nuclear pore complexes?

small polar molecules and macromolecules, highly selective

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59

what are nuclear fibrils?

unstructured regions of nuclear pore complexes

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60

what do nuclear fibrils prevent?

passage of large molecules

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61

what are nuclear localization signals?

specific amino acid sequence of proteins targeted for the nucleus

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62

what is the function of importins a/B (nuclear transport receptors)?

  • bind to protein, directs it through pore complex

  • disrupt nuclear fibril interaction, allows passage of nuclear proteins

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63

what does Ran control?

importins movement through the nuclear pore complex

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64

what are the two forms of Ran?

RanGDP and RanGTP

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65

describe RanGDP:

  • found in cytosol

  • guided into nucleus via NFT2

  • catalyzed to exchange GDP for GTP

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66

describe RanGTP:

  • found in nucleus

  • decreases importin/protein interaction

  • binds to importin and guides its transport out of nucleus

  • catalyzed to hydrolyze GTP to GDP

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67

what controls gene expression?

regulation of import and export of nuclear proteins

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68

how does the mitochondria obtain proteins?

  • synthesizes them inside mitochondria (1%)

  • imports from free cytosolic ribosomes (99%)

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69

why is importing of proteins complicated for the cell?

the double membrane of the mitochondria

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70

what does cytosolic Hsp70 recognize?

proteins destined for the mitochondria

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71

how does cytosolic Hsp70 utilize ATP hydrolysis?

to translocate mitochondrial proteins across the outer membrane

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72

what are the two protein sorting pathways?

mim1 translocator, tom complex

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73

what is the mim1 translocator utilized for?

single pass membrane protein in the outer membrane

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74

what occurs as proteins are translocated across the tom complex?

chaperone proteins bind

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75

what is the tim23 complex utilized for?

single pass membrane proteins

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76

how do the tom complex and tim23 complex interact?

translocated protein attaches to tim23 and inserted into the tim23 complex

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77

what is the tim22 complex utilized for?

multipass transmembrane proteins

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78

what is oxal translocase utilized for?

single pass membrane proteins

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79

what does mitochondrial hsp70 guide?

the protein to the oxal translocase

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80

describe how membrane fluidity can affect proteins entering into the mitochondrial matrix:

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81

what are the two pathways for proteins entering the ER:

stays embedded in the membrane OR leaves through the secretory pathway

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82

what happens to proteins once they enter the ER?

they will NOT return to the cytosol

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83

what do proteins require to enter the ER:

ribosomes synthesizing the proteins to be attached to the ER

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84

what are the two protein components which help guide ER signal sequences to the ER membrane?

signal recognition particle (SRP) and SRP receptor

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85

describe the signal recognition particle (SRP):

  • present in cytosol

  • bind to both the ribosome and the ER signal sequence as it emerges from the ribosomes

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86

SRP receptor:

  • embedded in the ER membrane

  • recognizes the SRP

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87

what are transport vesicles utilized for?

moving proteins to their destination

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88

what are transport vesicles composed of?

phospholipids

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89

what must transport vesicles do:

  • take with them only proteins appropriate to its destination

  • recognize and fuse with the appropriate organelle

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90

when do vesicles shed?

after budding is complete

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91

what function does the vesicle coat serve?

captures molecules for onward transport, shapes membrane into bud

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92

what are cargo receptors?

transmembrane proteins that bind soluble proteins for transport

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93

what is the function of adaptins?

  • secure clathrin coat to vesicle membrane

  • bind to cargo receptors, select cargo for transport

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94

what is the function of dynamin?

  • forms ring around neck of each budding vesicle

  • pinches vesicle

  • binds GTP

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95

you discover a cell line that forms coated pits of the vesicle but vesicle budding and the removal of the coat does not occur. what component of the budding process could be defective?

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96

what must transport vesicles display in order to ensure specificity?

molecular markers on the cell surface

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97

what are the two families of cytoplasmic microtubule motor proteins?

kinesins and dyneins

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98

which direction do kinesins move in?

towards the plus end

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99

what direction do dyneins move in?

towards the negative end

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100

what is the function of tethering proteins?

bind to rab proteins of the vesicle

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