Cytoskeleton Flashcards
1
Q
What is the primary function of actin filaments?
A
- Shape of the cell’s surface
- whole-cell locomotion
- pinching of one cell into two
2
Q
Three families of protein filaments
A
- Actin filaments
- Microtubules
- Intermediate filaments
3
Q
What role do microtubules play in the cell?
A
- Determine the positions of membrane-enclosed organelles
- Direct intracellular transport
- Form the mitotic spindle
4
Q
What is the function of intermediate filaments?
A
Provide mechanical strength
5
Q
What characterizes cytoskeletal systems?
A
Dynamic and adaptable, can change or persist according to need
6
Q
Where are actin filaments located in animal cells?
A
Underlie the plasma membrane
7
Q
Cell surface projections formed by Actin filaments:
A
1.Lamellipodia
2. Filopodia
8
Q
Where are microtubules found?
A
In a cytoplasmic array that extends to the cell periphery.
9
Q
What cellular structures are formed by microtubules?
A
Cilia and the mitotic spindle
10
Q
What is the role of intermediate filaments in epithelial cells?
A
Forms a protective cage for DNA
11
Q
The cytoskeleton is responsible for large-scale cellular _______.
A
polarity
12
Q
Polarized epithelial cells maintain the critical differences between the _____ and ______ .
A
Apical surface and basolateral surface
13
Q
What are the subunits that make up actin filaments?
A
Actin subunits
14
Q
What are the subunits that make up microtubules?
A
tubulin subunits
15
Q
What is the difference between the plus end and minus end of an actin filament?
A
Plus end grows faster than minus end
16
Q
Microtubules are built of ________ .
A
13 protofilaments
17
Q
True or False: Intermediate filament subunits are symmetrical and do not catalyze hydrolysis of nucleotide.
A
True
18
Q
Proteins that bind to the polarized cytoskeletal filament and us the energy derived from ATP hydrolysis to move along with it.
A
Motor Proteins
19
Q
Bacterial homolog of tubulin
A
FtsZ (forms z-ring)
20
Q
Bacterial homolog of actin
A
MreB and Mbl
21
Q
What are the three phases of in vitro polymerization of G-actin?
A
- Nucleation
- Elongation
- Steady-state
22
Q
What is the function of motor proteins in relation to cytoskeletal filaments?
A
Move along the filament using energy from ATP hydrolysis
23
Q
What is ParM in bacteria?
A
Bacterial actin homolog that helps in plasmid segregation
24
Q
What is the difference in elongation rates at the ends of an actin filament caused by?
A
Difference in critical concentration values at the two ends
25
What is the structural form of actin filaments?
Right-handed helix, 8nm wide
26
What is the nucleotide-binding cleft of actin filaments directed towards?
The minus end
27
The stiffness of of a filament can be characterized by its ________ .
Persistence length
28
What is the difference in elongation rates at the opposite ends of an actin filament caused by?
A difference in Cc values at the two ends
29
Which end of an actin filament can elongate when the plus end is capped?
Minus end
30
At what concentration of G-actin is there no filament growth?
Below Cc+
31
When G-actin concentration is between Cc+ and Cc-, where does growth occur?
Only at the (+) end
32
What happens when G-actin concentration is above Cc-?
No growth at both ends
33
What is the steady-state phase in actin dynamics?
G-actin concentrations intermediate between the Cc values for the (+) and (-) ends
34
What analogy describes the movement of newly added subunits in an actin filament?
As if on a treadmill
35
What is filament half-life?
A measure of how long an individual actin monomer spends in a filament
36
Keep the excess actin monomers in a sequestered state, preventing spontaneous polymerization
Thymosin
37
competes with thymosin for binding to actin monomers; promotes filament assembly by delivering monomers to the plus end
Profilin
38
Bring several actin subunits together to form a seed
Actin-nucleating factors
39
Nucleates actin filament growth from the minus end
Arp 2/3 Complex
40
Nucleates the growth of straight, unbranched filaments that can be cross-linked by other proteins to form parallel bundles.
Formins
41
What do actin filament-binding proteins do?
Alter filament behavior
42
Side-binding protein that stabilizes and stiffens actin filaments and can prevent actin filaments from interacting with other proteins.
Tropomyosin
43
Binds at the plus end, stabilizing an actin filament
Capping protein (Cap Z)
44
Responsible for the capping of exceptionally long-lived actin filaments in the muscle.
Tropomodulin
45
Proteins that break an actin filament into many smaller filaments, generating new filament ends
Severing proteins
46
Two types of severing proteins:
1. Gelsolin
2. Cofilin
47
What is gelsolin activated by?
High levels of cytosolic Ca2+
48
Acts as an actin depolymerizing factor that binds to and twists actin filaments
Cofilin
49
Actin filaments in animal cells are organized into several types of arrays:
1. Dendritic networks
2. Bundles
3. Web-like (gel-like) networks
50
What type of actin filament array is formed by the Arp 2/3 complex?
Dendritic networks
51
The motor protein that enables stress fibers and other contractile arrays to contract.
Myosin II
52
Facilitates the close packing of actin filaments
Fimbrin
53
Cross-links oppositely polarized actin filaments into loose bundles.
α-actinin
54
Promotes the formation of a loose and highly vicuous gel by clamping together two actin filaments.
Filamin
55
Mutations in the filamin A gene cause defects in ______ .
Nerve-cell migration during early embryonic development
56
What is the structure of spectrin?
Long, flexible protein made out of four elongated polypeptide chains
57
What do myosin heads do with ATP?
Bind and hydrolyze ATP
58
An elongated protein formed from two heavy chains and two copies of each of two light chains.
Myosin II
59
What are the motor proteins that interact with actin filaments?
Myosin
## Footnote
Myosin and actin motor proteins use structural changes to produce cyclic interactions.
60
A cylindrical structure 1-2 μm in diameter which consists of sarcomeres.
Myofibrils
61
A long, repeated chain of tiny contractile units about 2.2 μm long.
Sarcomeres
## Footnote
Sarcomeres give the vertebrate myofibril its striated appearance.
62
Is caused by the myosin filaments sliding past the actin thin filaments, with no change of either type of filament.
Sarcomere shortening
63
Components of a sarcomere:
1. Thin filaments
2. Thick filaments
64
What initiates muscle contraction?
Rise in cytosolic Ca2+ concentration
## Footnote
This signal passes to skeletal muscle from the nerve.
65
tube-like extensions of the muscle cell membrane that conduct electrical signals into the cell, triggering coordinated calcium release for muscle contraction.
Transverse tubules (T tubules)
66
Is an elongated protein that binds along the groove of the actin filament helix. It stabilizes and stiffens the filament.
Tropomyosin
## Footnote
It interferes with the binding of myosin head when in its normal state.
67
Troponin is a complex of three polypeptides:
troponin T, troponin I, and troponin C
68
What complex pulls tropomyosin out of its binding groove?
Troponin I-T complex
## Footnote
This action allows myosin heads to bind to actin.
69
Is a regulatory protein that activates MLCK in smooth muscle cells upon binding with calcium, leading to muscle contraction.
Calmodulin
70
Induces the phosphorylation of smooth muscle myosin on one of its two light chains upon activation of calmodulin.
Myosin light-chain kinase (MLCK)
## Footnote
It is activated by Ca2+-bound calmodulin.
71
A genetic condition commonly associated with heart enlargement, abnormally small coronary vessels, cardiac arrhythmias, and sudden death in young athletes.
Familial hypertrophic cardiomyopathy
## Footnote
It is a genetically dominant inherited condition.
72
Caused by a minor missense mutation in the cardiac actin gene, which results in early heart failure.
Dilated cardio myopathy
73
Two-headed myosin associated with organelle transport along actin filaments
Myosin V
## Footnote
It moves processively along actin filaments without letting go.
74
A heterodimer formed from α-tubulin and β-tubulin
Tubulin subunit
75
What is γ-tubulin?
A protein involved in the nucleation of microtubule growth
76
Specific intracellular location where microtubules are nucleated
Microtubule-organizing center (MTOC)
77
A complex that includes γ-tubulin and accessory proteins, forming a template for microtubule growth.
γ-tubulin ring complex (γ-TuRC)
78
A microtubule-organizing center near the nucleus that nucleates microtubules at their minus ends, while plus ends point outward, continuously growing and shrinking.
Centrosome
79
Cylindrical structures embedded in the centrosome, arranged at right angles.
Centrioles
80
Where microtubule nucleation takes place.
Pericentriolar material
81
The centrosome exhibits a _______ configuration with dynamic plus ends pointing outward
Aster-like
82
Proteins that bind to microtubules to stabilize them and mediate interactions with other cell components.
Microtubule-associated proteins (MAPs)
83
A MAP with a long projecting domain that forms bundles of widely spaced, stable microtubules
MAP2
84
A MAP with a shorter projecting domain that forms closely packed microtubule bundles.
tau
85
Binds to microtubule ends and pry protofilaments apart
Catastrophe factors (kinesin-13)
86
Protects microtubule minus ends from catastrophe factors
Nezha/Patronin
87
A protein that promotes microtubule polymerization and counters catastrophe factors
XMAP215
88
Proteins that accumulate at microtubule plus ends and assist in their growth
Plus-end tracking proteins (+TIPs)
89
Binds to tubulin subunits, preventing their addition to microtubules and promoting microtubule shrinkage.
Stathmin (Op18)
90
A protein composed of two subunits: one severs microtubules (via ATP hydrolysis), and the other directs katanin to the centrosome.
Katanin
91
Two major classes of microtubule-based motor proteins:
1. Kinesins
2. Dyneins
92
Carries membrane-enclosed organelles away from the cell body toward the axon terminal by walking toward the plus end of microtubules.
Kinesin-1
93
Composed of 1–3 heavy chains (with motor domains) and various intermediate, light-intermediate, and light chains.
Dyneins
94
Two major branches of the dynein family
1. Cytoplasmic dyneins
2. Axonemal dyneins
95
Dyneins that are homodimers of two heavy chains
Cytoplasmic dyneins
96
Dynein that handles organelle/mRNA trafficking, centrosome and nucleus positioning, and spindle construction in mitosis/meiosis
Cytoplasmic dynein I
97
Dynein found in ciliated eukaryotes, it transports materials from the cilia's tip to its base (intraflagellar transport).
Cytoplasmic dynein II
98
They enable the rapid microtubule sliding that powers cilia and flagella movement.
Axonemal dyneins (ciliary dyneins)
99
A protein complex associated with dynein to translocate organelles
Dynactin
100
What are cilia and flagella?
Hairlike structures built from microtubules that enable motility
101
The central, microtubule-based core of cilia and flagella, responsible for their movement.
Axoneme
102
What are axonemal dyneins?
Proteins that form bridges between neighboring doublet microtubules around the circumference of the axoneme
103
A nonmotile counterpart of cilia and flagella; specialized cellular compartments or organelles
Primary cilium
104
The most diverse intermediate filament family, composed of type I (acidic) and type II (neutral/basic) keratin proteins
Keratins
105
Intermediate filaments abundant in the axons of vertebrate neurons
Neurofilaments
106
Intermediate filaments found in muscle cells, where it forms a scaffold around the Z-disc of the sarcomere
Desmin
107
They facilitate cell-cell contact
Desmosomes
108
What do neurofilaments consist of?
NF-L, NF-M, and NF-H
109
Intermediate filaments are interconnected with other cytoskeletal components through linker proteins called _______ .
Plakins
110
Serve as scaffolds for proteins controlling various cellular processes including transcription and signal transduction
A-type lamins
111
A family of proteins that link the intermediate filament network to the rest of the cytoskeleton
Plakins
112
One-dimensional protrusions formed by migrating growth cones of neurons and some fibroblasts
Filopodia
113
Two-dimensional sheet like structures formed by epithelial cells and fibroblasts
Lamellipodia
114
What is retrograde flow in the context of cell migration?
Retrograde flow
115
The front end of the cell remains structurally and functionally distinct from the back end.
Cell Migration
116
Steps in the cycle of cell migration
1. Protrusion
2. Attachment
3. Traction
117
A step in the cell migration which involves pushing the plasma membrane out in front of the cell
Protrusion
118
In this step, the actin cytoskeleton connects
across the plasma membrane to the substratum
Attachment
119
In this step the bulk of the trailing cytoplasm is drawn forward
Traction
120
Types of protrusive structures:
1. Filopodia
2. Lamellipodia
3. Invadopodia
4. Blebbing
121
Formed by migrating growth
cones of neurons and some type of fibroblast; one-dimensional; contain a core
of long, bundled actin filaments
Filopodia
122
Formed by epithelial cells and fibroblast; two-dimensional sheetlike structures; contain a cross0linked mesh of actin filaments
Lamellipodia
123
Actin-rich protrusion; three-dimensional; important for cells to cross tissue barriers
Invadopodia and podosomes
124
Protrusion formation that depends on hydrostatic pressure within the cell; generated by the contraction of actin and myosin
Blebbing
125
Members of the Rho protein family
1. Cdc42
2. Rac
3. Rho
126
Promotes actin polymerization and bundling to form filopodia.
Cdc42
127
Activates actin polymerization at the cell periphery and forms sheet-like lamellipodial extensions.
Rac
128
Bundles actin filaments with myosin II filaments into stress fibers and clusters integrins to form focal adhesions.
Rho
