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Cell Bio > Chapter 17- Cytoskeleton > Flashcards

Chapter 17- Cytoskeleton Flashcards

1
Q

Three types of protein filaments in the cytoskeleton

A

Intermediate filaments, Microtubules, actin filaments

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2
Q

are the most stable filaments

A

In termediate filaments (IFs)

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3
Q

organize and interconnect tissues, protect against mechanical stress, serve as scaffolds for signaling molecules

A

Intermediate filaments

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4
Q

IF subunits form what kind of tetramers

A

Anti parallel and staggered

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5
Q

In the IF subunit, there’d a conserved rod domain that’s involved in

A

Assembly

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6
Q

__ tetramers assemble into __ 10 nm filament

A

8, non-polarized

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7
Q

IFs are relatively __

A

Stable

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8
Q

most resistant to extraction
of the cytoskeletal filaments

A

IF

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9
Q

Four major classes of IF

A

Cytoplasmic: keratin, vimentin, neurofilaments

Nuclear: nuclear lamins

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10
Q

Origin of tumor cells can be identified by

A

IF type

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11
Q

What class of IF protect epithelial cells from mechanical damage

A

Keratins and junctions

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12
Q

What IF class are found in other tissues (connective tissue, muscle cells, and glial cells)

A

Vimentins

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13
Q

What IF class support axons in nerve cells

A

Neurofilaments

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14
Q

What IF class forms the nuclear lamina that supports nuclear envelope

A

Lamins

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15
Q

Intermediate filaments protect cells against mechanical stress, most obvious in the

A

Skin by keratins

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16
Q

form basket-like arrays that bind to desmosomes and
connect neighboring cells

A

Keratins

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17
Q

Defects in keratins or junction proteins lead to

A

Cell rupture

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18
Q

In an IF subunit, unstructured domains at__ termini confer specific functions

A

Amino and carbonyl terminal (2 n and 2 c terminal ends)

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19
Q

intercellular junctions that link the keratin filaments of one cell to those in a neighboring cell

A

De smosomes

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20
Q

type of skin blistering disease, caused by a defect in keratin expressed in bottom layer of skin

A

EBS

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21
Q

Nuclear lamins form an IF network __ the nucleus

A

Inside

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22
Q

Nuclear lamins form a

A

2D mesh work on nuclear envelope

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23
Q

disassembles the network on nuclear envelope, driving nuclear envelope breakdown during mitosis

A

Phosphorylation of lamins by kinases

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24
Q

Dephosphorylation of nuclear lamins leads to

A

Reassembly

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25
Q

You wish to study the assembly of the nuclear lamina in cells. Would the following conditions be expected to enhance or disfavor assembly of the nuclear lamina?

(a) Addition of protein kinase inhibitors

(b) Addition of phosphatase inhibitors

A

A. Enhance: Phosphorylation of lamins drives disassembly of
the nuclear lamina, so inhibiting the kinases that
phosphorylate lamins will enhance assembly

B. Disfavor: Dephosphorylation of lamins promotes reassembly
of the nuclear lamina, so inhibiting the phosphatases that
dephosphorylate lamins will disfavor assembly

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26
Q

Cadherins inside of the

A

Desomosome

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27
Q

Desomosome binds our

A

Cadherins and keratin filaments

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28
Q

hollow tubes with structurally distinct ends, organizing the interior of the cell

A

Microtubules

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29
Q

The __ is the major MT-organizing center

A

centrosome

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30
Q

networks are maintained by assembly & disassembly

A

Microtubules

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31
Q

Growing microtubules exhibit

A

dynamic instability

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32
Q

Motor proteins drive…

A

intracellular transport

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33
Q

Cilia & flagella contain MTs moved by

A

dynein

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34
Q

Largest, most rigid filaments

A

Microtubules

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35
Q

Primary intracellular railroad track, Primary determinant of cell polarity

A

Microtubules

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36
Q

The building block of MTs is the…

A

a/b tubulin heterodimer

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37
Q

MTs are hollow tubes made of __ protofilaments

A

13

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38
Q

linear chain of tubulin dimers

A

protofilament

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39
Q

MTs have what kind of ends?

A

plus (fast-growing) &
minus (slow-growing) ends

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40
Q

In most animal cells, the centrosome organizes an
array of MTs that…

A

radiates outward through the
cytosol

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41
Q

Centrosomes are duplicated to form the

A

mitotic spindle poles

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42
Q

Microtubule-organizing centers form __ at the base of cilia and flagella

A

basal bodies

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43
Q

Microtubule-organizing centers (MTOCs) bind to __ ends of the Microtubules, allowing __ end to extend outward

A

Minus ends, plus ends

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44
Q

is a MT-organizing center (MTOC)

A

Centrosome

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45
Q

The centrosome contains __ centrioles and many ____

A

2, gamma- tubulin ring complexes ( yTURC)

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46
Q

yTURC binds __ ends of tubulin subunits and promotes __ of MTs

A

minus, assembly

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47
Q

Growing microtubules show

A

dynamic instability, shrinks independently of its neighbor

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48
Q

enables the cell to continuously monitor its environment

A

Dynamic instability

49
Q

Dynamic instability results from

A

GTP hydrolysis

50
Q

Addition of GTP-tubulin at the __ end of the MT forms a ____

A

plus, stable GTP cap

51
Q

Microtubles with __ tubulin caps depolymerize rapidly

52
Q

GDP-tubulin dimers must exchange their __ for __ before they can be
added to a growing MT

A

GDP for GTP

53
Q

MT capping proteins stabilize what ends

54
Q

__ of MTs can drive changes in cell shape and allow microtubules to form long distance tracks for transport

A

Selective stabilization

55
Q

A polarized MT array (minus ends in the cell body; plus ends pointing
towards the axon terminals) provides…

A

Tracks for transport

56
Q

Cargoes interact with __, which move them along MTs

A

motor proteins

57
Q

__ walk to the MT plus end,
___ walk to the minus end

A

Kinesins, dyneins

58
Q

Globular head domains (also called “motor domains”) bind

59
Q

Both kinesin and dynein are members of large gene families with __
motor domains & __ tail domains

A

Conserved, variable

60
Q

Defects in MTs & motor proteins are linked to

A

Nerve degeneration

61
Q

drives extension of the ER network along MT network

62
Q

places Golgi close to the centrosome

63
Q

Cilia & flagella contain stable MTs moved by

A

ciliary dynein

64
Q

move fluid or mucus over the surface of epithelia

move individual cells through fluid

A

Cilia

Flagella

65
Q

Cilia and flagella share a conserved structure:

A

9+2” MT array

66
Q

Arrangement of ciliary dyneins creates inner and outer __ arms

67
Q

Without linkages between neighboring MT doublets, MTs ___

With linkages, MTs __

A

Slide apart, bend

68
Q

A disease that results from defects in ciliary dyneins

A

Kartagener’s syndrome

69
Q

Will the following scenarios promote microtubule growth?
(a ) Addition of a drug that inhibits hydrolysis of the GTP carried out
by tubulin dimers

(b) Addition of a drug that inhibits exchange of GDP for GTP by
tubulin dimers

(c) Addition of a drug that increases the affinity of GDP-tubulin
dimers for other tubulin dimers

A

A. Ye s – Inhibition of GTP hydrolysis promotes the formation of a GTP cap. Microtubules with GTP caps will continually elongate.

B. No – Tubulin dimers must exchange their GDP for GTP before being added to a microtubule plus end.

C. Yes – Increasing the affinity of GDP-tubulin for other tubulin dimers will prevent the dissociation of GDP-tubulin dimers from microtubule plus ends in the event of loss of the GTP cap.

70
Q

filaments are thin and flexible

71
Q

are cross-linked to form stable bundles that support
membranes (microvilli in the gut, stereocilia in the inner ear)

72
Q

Actin filaments are structurally
asymmetric and…

73
Q

Actin filaments have what end

A

plus end
(fast assembly) and a minus end
(slow assembly)

74
Q

ATP-actin adds preferentially to the

75
Q

Actin hydrolyzes its bound ATP soon after being

A

incorporated into the filament

76
Q

Actin monomers add to the __ end faster than ATP is hydrolyzed, so the…

A

plus, plus end grows

77
Q

At the __ end, ATP is hydrolyzed faster than new monomers can be added,
so the __ end depolymerizes (In actin)

78
Q

How does actin and microtubules differ with plus and minus ends

A

Microtubules can grow and shrink at the plus end, but in actin the plus end only grows

79
Q

Cells initiate and control actin filament assembly with

A

nucleating factors (e.g. formin, ARP complex)

80
Q

In cells, the actin concentration is very

81
Q

What uses “monomer-sequestering” proteins (e.g. profilin, thymosin) that bind to __ monomers and prevent them from adding to the ends of actin filaments.

82
Q

Often thicker & more complex than the cortex of red blood cells

A

actin-rich cortex

83
Q

Cell locomotion depends on _ different actin
networks

84
Q

actin polymerization in the lamellipodium (i.e. the “leading edge”)

A

Dynamic actin network

85
Q

actin arrays making focal contacts with the extracellular matrix through integrins

A

Stabilized actin network

86
Q

actin networks pulling up the rear of the cell

A

Contractile

87
Q

Forward movement of the lamellipodium depends on

A

branched actin polymerization

88
Q

As filaments “age”, actin undergoes

A

ATP hydrolysis

89
Q

ADP-actin is disassembled at the

90
Q

Actin monomers add to filament _ ends

A

plus, pushing membrane forward

91
Q

binds to the side of an existing actin filament and nucleates a
new filament, which grows out at an angle, making a “branch”

A

ARP complex

92
Q

assemble actin filaments found in filopodia

93
Q

Formin promotes the assembly of ___ filaments

A

straight, unbranched

94
Q

Formins bind to the actin filament __ end

95
Q

are transmembrane proteins that bind to the extracellular
matrix and connect it to the actin cytoskeleton at focal contacts

96
Q

Actin attachment to substrate by

A

focal contacts

97
Q

Contractile filaments bring up the…

A

rear of the cell

98
Q

Stable actin filaments interact with

99
Q

a motor protein that slides actin filaments to generate contraction

100
Q

Extracellular signals control the arrangement of actin
filaments using

A

monomeric GTPases

101
Q

promotes assembly of contractile networks

102
Q

promotes assembly of branched actin networks (using ARP complex)

103
Q

promotes assembly of straight actin filaments (by activating formin)

104
Q

Myosin I found in

A

Membrane binding

105
Q

Myosin II found in

A

muscle & contractile fibers

106
Q

Myosin II is a

107
Q

Myosin heads walk towards the _ end of actin filaments

108
Q

Muscle contraction depends on _
bundles of actin & myosin II filaments

109
Q

Muscle contraction is triggered by a sudden rise in the intracellular

A

Ca2+ concentration

110
Q

a string of sarcomeres

111
Q

The cytoplasm of muscle cells is filled with organized
arrays of contractile proteins called

A

myofibrils

112
Q

the basic unit of contraction

113
Q

Motor nerve releases

A

acetylcholine

114
Q

T-tubules extend inward from plasma membrane and contact the

A

sarcoplasmic reticulum

115
Q

VG channels of calcium are in the __ and release channel in __

A

T tubule, SR

116
Q

In the absence of Ca2+, __ binds along the actin filaments & blocks
myosin from binding

A

tropomyosin

117
Q

In contraction sarcomere shortens by

A

1 micrometer

118
Q

Which of the items below doesn’t describe something similar about the polymerization mechanisms of actin and microtubules?

A. The rate of subunit addition is faster at the plus end than at the minus end

B. Depolymerization initiates at the plus ends of filaments

C. Nucleotide hydrolysis promotes the depolymerization of filaments

D. Free subunits (actin and tubulin) bind nucleoside triphosphates

A

B (actin doesn’t depolymerize)

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