Chapter 17- Cytoskeleton Flashcards
1
Q
Three types of protein filaments in the cytoskeleton
A
Intermediate filaments, Microtubules, actin filaments
2
Q
are the most stable filaments
A
In termediate filaments (IFs)
3
Q
organize and interconnect tissues, protect against mechanical stress, serve as scaffolds for signaling molecules
A
Intermediate filaments
4
Q
IF subunits form what kind of tetramers
A
Anti parallel and staggered
5
Q
In the IF subunit, there’d a conserved rod domain that’s involved in
A
Assembly
6
Q
__ tetramers assemble into __ 10 nm filament
A
8, non-polarized
7
Q
IFs are relatively __
A
Stable
8
Q
most resistant to extraction
of the cytoskeletal filaments
A
IF
9
Q
Four major classes of IF
A
Cytoplasmic: keratin, vimentin, neurofilaments
Nuclear: nuclear lamins
10
Q
Origin of tumor cells can be identified by
A
IF type
11
Q
What class of IF protect epithelial cells from mechanical damage
A
Keratins and junctions
12
Q
What IF class are found in other tissues (connective tissue, muscle cells, and glial cells)
A
Vimentins
13
Q
What IF class support axons in nerve cells
A
Neurofilaments
14
Q
What IF class forms the nuclear lamina that supports nuclear envelope
A
Lamins
15
Q
Intermediate filaments protect cells against mechanical stress, most obvious in the
A
Skin by keratins
16
Q
form basket-like arrays that bind to desmosomes and
connect neighboring cells
A
Keratins
17
Q
Defects in keratins or junction proteins lead to
A
Cell rupture
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)
19
Q
intercellular junctions that link the keratin filaments of one cell to those in a neighboring cell
A
De smosomes
20
Q
type of skin blistering disease, caused by a defect in keratin expressed in bottom layer of skin
A
EBS
21
Q
Nuclear lamins form an IF network __ the nucleus
A
Inside
22
Q
Nuclear lamins form a
A
2D mesh work on nuclear envelope
23
Q
disassembles the network on nuclear envelope, driving nuclear envelope breakdown during mitosis
A
Phosphorylation of lamins by kinases
24
Q
Dephosphorylation of nuclear lamins leads to
A
Reassembly
25
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. 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
26
Cadherins inside of the
Desomosome
27
Desomosome binds our
Cadherins and keratin filaments
28
hollow tubes with structurally distinct ends, organizing the interior of the cell
Microtubules
29
The __ is the major MT-organizing center
centrosome
30
networks are maintained by assembly & disassembly
Microtubules
31
Growing microtubules exhibit
dynamic instability
32
Motor proteins drive…
intracellular transport
33
Cilia & flagella contain MTs moved by
dynein
34
Largest, most rigid filaments
Microtubules
35
Primary intracellular railroad track, Primary determinant of cell polarity
Microtubules
36
The building block of MTs is the…
a/b tubulin heterodimer
37
MTs are hollow tubes made of __ protofilaments
13
38
linear chain of tubulin dimers
protofilament
39
MTs have what kind of ends?
plus (fast-growing) &
minus (slow-growing) ends
40
In most animal cells, the centrosome organizes an
array of MTs that…
radiates outward through the
cytosol
41
Centrosomes are duplicated to form the
mitotic spindle poles
42
Microtubule-organizing centers form __ at the base of cilia and flagella
basal bodies
43
Microtubule-organizing centers (MTOCs) bind to __ ends of the Microtubules, allowing __ end to extend outward
Minus ends, plus ends
44
is a MT-organizing center (MTOC)
Centrosome
45
The centrosome contains __ centrioles and many ____
2, gamma- tubulin ring complexes ( yTURC)
46
yTURC binds __ ends of tubulin subunits and promotes __ of MTs
minus, assembly
47
Growing microtubules show
dynamic instability, shrinks independently of its neighbor
48
enables the cell to continuously monitor its environment
Dynamic instability
49
Dynamic instability results from
GTP hydrolysis
50
Addition of GTP-tubulin at the __ end of the MT forms a ____
plus, stable GTP cap
51
Microtubles with __ tubulin caps depolymerize rapidly
GDP
52
GDP-tubulin dimers must exchange their __ for __ before they can be
added to a growing MT
GDP for GTP
53
MT capping proteins stabilize what ends
Plus
54
__ of MTs can drive changes in cell shape and allow microtubules to form long distance tracks for transport
Selective stabilization
55
A polarized MT array (minus ends in the cell body; plus ends pointing
towards the axon terminals) provides…
Tracks for transport
56
Cargoes interact with __, which move them along MTs
motor proteins
57
__ walk to the MT plus end,
___ walk to the minus end
Kinesins, dyneins
58
Globular head domains (also called “motor domains”) bind
ATP & MT
59
Both kinesin and dynein are members of large gene families with __
motor domains & __ tail domains
Conserved, variable
60
Defects in MTs & motor proteins are linked to
Nerve degeneration
61
drives extension of the ER network along MT network
Kinesin
62
places Golgi close to the centrosome
Dynein
63
Cilia & flagella contain stable MTs moved by
ciliary dynein
64
move fluid or mucus over the surface of epithelia
move individual cells through fluid
Cilia
Flagella
65
Cilia and flagella share a conserved structure:
9+2” MT array
66
Arrangement of ciliary dyneins creates inner and outer __ arms
dynein
67
Without linkages between neighboring MT doublets, MTs ___
With linkages, MTs __
Slide apart, bend
68
A disease that results from defects in ciliary dyneins
Kartagener’s syndrome
69
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. 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
filaments are thin and flexible
Actin
71
are cross-linked to form stable bundles that support
membranes (microvilli in the gut, stereocilia in the inner ear)
Actin
72
Actin filaments are structurally
asymmetric and...
polar
73
Actin filaments have what end
plus end
(fast assembly) and a minus end
(slow assembly)
74
ATP-actin adds preferentially to the
plus end
75
Actin hydrolyzes its bound ATP soon after being
incorporated into the filament
76
Actin monomers add to the __ end faster than ATP is hydrolyzed, so the...
plus, plus end grows
77
At the __ end, ATP is hydrolyzed faster than new monomers can be added,
so the __ end depolymerizes (In actin)
minus
78
How does actin and microtubules differ with plus and minus ends
Microtubules can grow and shrink at the plus end, but in actin the plus end only grows
79
Cells initiate and control actin filament assembly with
nucleating factors (e.g. formin, ARP complex)
80
In cells, the actin concentration is very
high
81
What uses “monomer-sequestering” proteins (e.g. profilin, thymosin) that bind to __ monomers and prevent them from adding to the ends of actin filaments.
actin
82
Often thicker & more complex than the cortex of red blood cells
actin-rich cortex
83
Cell locomotion depends on _ different actin
networks
three
84
actin polymerization in the lamellipodium (i.e. the “leading edge”)
Dynamic actin network
85
actin arrays making focal contacts with the extracellular matrix through integrins
Stabilized actin network
86
actin networks pulling up the rear of the cell
Contractile
87
Forward movement of the lamellipodium depends on
branched actin polymerization
88
As filaments “age”, actin undergoes
ATP hydrolysis
89
ADP-actin is disassembled at the
minus end
90
Actin monomers add to filament _ ends
plus, pushing membrane forward
91
binds to the side of an existing actin filament and nucleates a
new filament, which grows out at an angle, making a “branch”
ARP complex
92
assemble actin filaments found in filopodia
Formins
93
Formin promotes the assembly of ___ filaments
straight, unbranched
94
Formins bind to the actin filament __ end
plus
95
are transmembrane proteins that bind to the extracellular
matrix and connect it to the actin cytoskeleton at focal contacts
Integrins
96
Actin attachment to substrate by
focal contacts
97
Contractile filaments bring up the...
rear of the cell
98
Stable actin filaments interact with
myosin II
99
a motor protein that slides actin filaments to generate contraction
myosin II
100
Extracellular signals control the arrangement of actin
filaments using
monomeric GTPases
101
promotes assembly of contractile networks
Rho
102
promotes assembly of branched actin networks (using ARP complex)
Rac
103
promotes assembly of straight actin filaments (by activating formin)
Cdc42
104
Myosin I found in
Membrane binding
105
Myosin II found in
muscle & contractile fibers
106
Myosin II is a
dimer
107
Myosin heads walk towards the _ end of actin filaments
plus
108
Muscle contraction depends on _
bundles of actin & myosin II filaments
organized
109
Muscle contraction is triggered by a sudden rise in the intracellular
Ca2+ concentration
110
a string of sarcomeres
myofibril
111
The cytoplasm of muscle cells is filled with organized
arrays of contractile proteins called
myofibrils
112
the basic unit of contraction
sarcomere
113
Motor nerve releases
acetylcholine
114
T-tubules extend inward from plasma membrane and contact the
sarcoplasmic reticulum
115
VG channels of calcium are in the __ and release channel in __
T tubule, SR
116
In the absence of Ca2+, __ binds along the actin filaments & blocks
myosin from binding
tropomyosin
117
In contraction sarcomere shortens by
1 micrometer
118
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
B (actin doesn’t depolymerize)
