The Cytoskeleton Flashcards
(216 cards)
1
Q
What is the primary function of the actin cytoskeleton?
A
Performs a wide range of functions in diverse cell types
2
Q
What are actin subunits also known as?
A
Globular or G-actin
3
Q
What are the three isoforms of actin found in vertebrates?
A
- α-actin
- β-actin
- γ-actin
4
Q
Which isoform of actin is expressed only in muscle cells?
A
α-actin
5
Q
What are the two ends of an actin filament called?
A
- Plus end (barbed end)
- Minus end (pointed end)
6
Q
What structural form do actin subunits take when assembled?
A
Filamentous or F-actin
7
Q
What is the rate-limiting step in the formation of actin filaments?
A
Nucleation
8
Q
What is the critical concentration (Cc) in actin polymerization?
A
The concentration of free subunits at steady state
9
Q
What happens during the lag phase of actin polymerization?
A
Small, unstable oligomers gradually form a stable nucleus
10
Q
What occurs during the elongation phase of actin polymerization?
A
Subunits are added quickly to the ends of the nucleated filaments
11
Q
What is dynamic instability in the context of microtubules?
A
The alternating periods of growth and rapid disassembly
12
Q
What is an ATP cap on an actin filament?
A
A cap of subunits containing ATP at the growing end
13
Q
What happens to ATP once it is incorporated into the actin filament?
A
It is hydrolyzed to ADP
14
Q
What is the role of nucleotide hydrolysis in filament dynamics?
A
Reduces binding affinity and increases likelihood of dissociation
15
Q
How does the rate of addition of subunits differ between the plus and minus ends of an actin filament?
A
The plus end grows faster than the minus end
16
Q
What type of proteins frequently cross-link and bundle actin filaments together?
A
Accessory proteins
17
Q
What happens to the concentration of free subunits as polymerization proceeds?
A
It declines until it reaches the critical concentration
18
Q
What is the relationship between the rates of addition and loss at the two ends of a polymer?
A
The ratio koff/kon must be the same at both ends
19
Q
What structural feature allows actin filaments to have different growth rates at each end?
A
Conformational changes of subunits upon polymerization
20
Q
What happens to the binding affinity of a subunit when nucleotide hydrolysis occurs?
A
It reduces the binding affinity for neighboring subunits, making it more likely to dissociate
21
Q
What is the critical concentration (Cc) for polymer growth?
A
C = Cc when kT_onC = kD_off
22
Q
What is treadmilling in the context of actin filaments?
A
A process where subunits undergo net assembly at the plus end and net disassembly at the minus end
23
Q
What is the relationship between critical concentrations at the two ends of a polymer?
A
Cc (minus end) > Cc (plus end)
24
Q
What condition allows polymerization to proceed at both ends of a polymer?
A
The concentration of free monomer must be above Cc for the plus end but below Cc for the minus end
25
What effect do preexisting seeds have on filament growth?
They eliminate the lag phase in filament growth
26
What is the significance of the free-energy change (∆G) in filament elongation?
Elongation occurs when ∆G is less than zero
27
What happens to ATP hydrolysis in actin filaments?
It is accelerated when subunits are incorporated into filaments
28
What forms can actin filaments take based on nucleotide binding?
ATP-bound T form and ADP-bound D form
29
What is the role of actin-binding proteins?
They influence filament dynamics and organization
30
What is the function of the Arp2/3 complex?
Nucleates actin filament growth and remains bound to the filament
31
What is the mechanism by which formins nucleate actin filaments?
They bring several actin subunits together to form a seed
32
Fill in the blank: The free actin subunits are primarily in the _______ form.
T form
33
What is the effect of chemical inhibitors on actin and microtubules?
They can stabilize or destabilize filaments, affecting dynamic behavior
34
What are the two main factors that catalyze actin nucleation?
* Arp2/3 complex
* Formins
35
What protein nucleates assembly to form a branched network in actin filaments?
Arp2/3 complex
## Footnote
The Arp2/3 complex is essential for actin filament nucleation and creates a branched structure.
36
What role does profilin play in actin filament assembly?
Binds monomers and concentrates them at sites of filament assembly
## Footnote
Profilin enhances the availability of actin monomers for polymerization.
37
What is the function of the capping protein in actin filaments?
Prevents assembly and disassembly at the plus end
## Footnote
Capping proteins stabilize actin filaments by inhibiting growth and shrinkage.
38
What does tropomodulin do in actin filaments?
Prevents assembly and disassembly at the minus end
## Footnote
Tropomodulin stabilizes filaments and modulates the binding of other accessory proteins.
39
What is the function of gelsolin in actin dynamics?
Severs filaments and binds to the plus end
## Footnote
Gelsolin facilitates the remodeling of actin filaments.
40
What are formins and their role in actin filament assembly?
Dimeric proteins that nucleate growth of unbranched filaments
## Footnote
Formins maintain association with the growing plus end of actin filaments.
41
How does the Arp2/3 complex facilitate actin filament nucleation?
Requires a nucleation-promoting factor (NPF)
## Footnote
NPFs activate the Arp2/3 complex, enhancing its ability to nucleate new filaments.
42
What is the significance of actin filament nucleation at the plasma membrane?
Highest density of actin filaments is at the cell periphery
## Footnote
This localization influences cell shape and movement.
43
What happens to an uncapped actin filament after ATP hydrolysis?
Depolymerizes rapidly, particularly at its plus end
## Footnote
The absence of capping proteins allows for rapid disassembly of the filament.
44
What is the role of tropomyosin in actin filaments?
Stabilizes and stiffens the filament, prevents interaction with other proteins
## Footnote
Tropomyosin is crucial for muscle contraction control.
45
What are the effects of plus-end capping proteins on filament dynamics?
Stabilizes filament at the plus end, reduces growth and depolymerization rates
## Footnote
Capping proteins alter the dynamics of filament assembly and disassembly.
46
What do actin cross-linking proteins do?
Influence the organization and dynamics of actin networks
## Footnote
Cross-linking proteins can bundle or mesh actin filaments depending on their structure.
47
How does fimbrin affect actin filament organization?
Contributes to tight packing of parallel bundles of actin filaments
## Footnote
Fimbrin is important in structures like microvilli.
48
What is the role of α-actinin in actin filament organization?
Cross-links oppositely polarized actin filaments into loose bundles
## Footnote
α-actinin allows for the binding of myosin and formation of contractile structures.
49
What is the function of end-binding proteins in actin dynamics?
Affect filament dynamics even at low levels
## Footnote
End-binding proteins can significantly alter actin architecture.
50
What is the role of fimbrin in actin filament organization?
Fimbrin cross-links actin filaments into parallel bundles, excluding myosin and preventing contractility.
## Footnote
This results in non-contractile structures compared to those organized by α-actinin.
51
How does α-actinin affect actin filaments?
α-Actinin cross-links oppositely polarized actin filaments into loose bundles, allowing myosin binding and forming contractile actin bundles.
## Footnote
The bundling by α-actinin is mutually exclusive with that of fimbrin.
52
Where does actin polymerization primarily initiate in animal cells?
At the plasma membrane where nucleation proteins are activated.
53
What is the effect of severing proteins on actin filaments?
Severing proteins break actin filaments into smaller pieces, generating new filament ends that can either nucleate elongation or promote depolymerization.
54
How does gelsolin function in actin filament dynamics?
Gelsolin is activated by high levels of Ca2+, severs actin filaments, and caps the new plus end.
## Footnote
It interacts with both exposed and hidden sites on the filament.
55
What is the function of cofilin in actin filament regulation?
Cofilin binds to ADP-containing actin filaments, forcing them to twist and destabilizing them for easier severing.
56
What characteristic of actin filaments does cofilin preferentially target?
Cofilin preferentially binds to ADP-containing actin filaments rather than ATP-containing filaments.
57
What nucleating protein is responsible for branched actin networks?
The Arp2/3 complex.
58
What nucleating protein is responsible for straight actin bundles?
Formins.
59
What are filopodia and lamellipodia?
Filopodia are spike-like projections with long, bundled actin filaments; lamellipodia are sheet-like structures with a cross-linked mesh of actin filaments.
60
What characterizes amoeboid cell migration?
Formation of a three-dimensional pseudopod through explosive actin polymerization at the leading edge.
61
What occurs during blebbing cell migration?
The plasma membrane detaches from the underlying cortex and is pushed out by hydrostatic pressure.
62
How does cell migration relate to the actin cytoskeleton?
Cell migration relies on the actin-rich cortex beneath the plasma membrane to drive protrusion and movement.
63
What is the primary mechanism driving amoeboid cell migration?
Explosive actin polymerization at the leading edge
## Footnote
This results in the formation of pseudopodia.
64
What is the role of cofilin in actin dynamics?
Disassembles older ADP-bound actin filaments
## Footnote
This occurs behind the leading edge of the cell.
65
What are the characteristics of mesenchymal cell migration?
Requires firm attachment to substratum, slow movement rates
## Footnote
Movement rates are less than 1 μm per minute.
66
What distinguishes amoeboid cell migration from mesenchymal cell migration?
Amoeboid migration is faster and does not rely heavily on integrin-based attachments
## Footnote
Typical of white blood cells like neutrophils.
67
What is blebbing in the context of cell migration?
Formation of a membrane protrusion when the plasma membrane detaches from the actin cortex
## Footnote
This process is driven by hydrostatic pressure.
68
What is the significance of actin filament polarity?
Actin filaments can undergo treadmilling, assembling at the plus end while depolymerizing at the minus end
## Footnote
This dynamic behavior is crucial for cell movement.
69
What do nucleation factors like the Arp2/3 complex and formins do?
Promote formation of branched and parallel actin filaments, respectively
## Footnote
They are key in regulating actin dynamics.
70
What is the role of myosin motors in cell migration?
Generate contractile forces to move the cell body forward
## Footnote
This is essential for the cell's locomotion.
71
What provides mechanical strength to animal cells?
Connections between actin arrays and the plasma membrane
## Footnote
This allows for the formation of various cellular structures.
72
What is a crucial feature of the actin cytoskeleton?
It can form contractile structures that cross-link and slide actin filaments relative to one another through the action of myosin motor proteins.
73
What important functions do actin–myosin assemblies perform?
* Cell migration
* Muscle contraction
74
What is myosin II composed of?
* Two heavy chains
* Two copies of each of two light chains
75
What does the N-terminus of each heavy chain of myosin II contain?
A globular head domain that contains the force-generating machinery.
76
What structural feature mediates heavy-chain dimerization in myosin II?
A long α-helical amino acid sequence that forms an extended coiled-coil.
77
What is the arrangement of myosin heads in skeletal muscle thick filaments?
Oriented in opposite directions at the two ends of the thick filament.
78
What process does each myosin head perform?
Binds and hydrolyzes ATP.
79
How do myosin heads move along actin filaments?
Using the energy of ATP hydrolysis to walk toward the plus end of an actin filament.
80
What is the role of myosin II in skeletal muscle contraction?
Drives efficient sliding of actin filaments, resulting in powerful contraction.
81
What do motor proteins use to produce cyclic interactions with a cytoskeletal filament?
Structural changes in their ATP-binding sites.
82
What is the result of ATP binding to the myosin head?
Reduces the affinity of the head for actin.
83
What triggers the power stroke in myosin II?
Release of inorganic phosphate produced by ATP hydrolysis.
84
What are myofibrils?
The basic contractile elements of the muscle cell.
85
What is a sarcomere?
A miniature, precisely ordered array of parallel and partly overlapping thin and thick filaments.
86
What composes the thin filaments in a sarcomere?
Actin and associated proteins.
87
What is the role of ATP in muscle contraction?
Drives the sliding of actin filaments against myosin II filaments.
88
What is the arrangement of myosin filaments observed in cross-section by electron microscopy?
Regular hexagonal lattice.
89
What happens to the length of the sarcomere during contraction?
It shortens.
90
What structural feature connects movements at the ATP-binding cleft in myosin II's head?
A pistonlike helix.
91
What causes sarcomere shortening?
Myosin filaments sliding past actin thin filaments
92
How do myosin heads interact with actin filaments?
Independent myosin heads walk toward the plus ends of thin filaments
93
What proteins anchor actin filament plus ends in the Z disc?
CapZ and α-actinin
94
What is the function of tropomyosin in muscle contraction?
Stabilizes actin filaments along their length
95
What role does nebulin play in muscle filaments?
Stabilizes actin filaments and stretches from the Z disc
96
What is the function of titin in muscle cells?
Positions thick filaments and acts as a molecular spring
97
What initiates muscle contraction?
A sudden rise in cytosolic Ca2+ concentration
98
How does the muscle cell receive the signal to contract?
Through an action potential from the nerve
99
What is the function of T tubules in muscle cells?
Relay the action potential to all myofibrils
100
What triggers the opening of Ca2+-release channels in the sarcoplasmic reticulum?
Activation of Ca2+ channels in the T-tubule membrane
101
What is the role of the Ca2+-ATPase in muscle contraction?
Pumps Ca2+ back into the sarcoplasmic reticulum
102
What proteins regulate contraction in vertebrate skeletal muscle?
Tropomyosin and troponin
103
What are the components of the troponin complex?
Troponins T, I, and C
104
What happens to tropomyosin when Ca2+ levels rise?
Tropomyosin shifts to allow myosin heads to bind to actin
105
What mechanism regulates contraction in smooth muscle?
Calmodulin-dependent phosphorylation of myosin light chain
106
What is the shape and structure of smooth muscle cells?
Spindle-shaped and elongated with a single nucleus
107
How does contraction of smooth muscle affect the intestine?
Shortens and narrows the intestine
108
What is the orientation of the outer layer of smooth muscle cells?
The long axis of its cells extends parallel along the length of the intestine.
109
What happens when the inner layer of smooth muscle contracts?
It causes the intestine to become narrower.
110
What is the effect of contraction of both layers of smooth muscle?
It squeezes material through the intestine.
111
What proteins are involved in the contractile apparatus of smooth muscle cells?
Actin and myosin.
112
How does the contraction speed of smooth muscle compare to skeletal muscle?
Smooth muscle contraction occurs relatively slowly, requiring nearly a second.
113
What role do actin–myosin II assemblies play in non-muscle cells?
They enable dynamic changes in cell morphology.
114
How are non-muscle contractile bundles regulated?
By myosin phosphorylation rather than by troponin.
115
What is a function of actin–myosin II bundles in non-muscle cells?
They provide mechanical support by assembling into stress fibers.
116
What do contractile bundles contribute to during cell division?
They generate the force for cytokinesis.
117
What is the unique movement direction of myosin VI?
It moves toward the minus end of an actin filament.
118
What is the primary function of myosin I proteins?
Involved in intracellular organization and protrusion of actin-rich structures.
119
What is the role of myosin V?
Involved in organelle transport along actin filaments.
120
What is the significance of ATP hydrolysis in myosins?
Myosins convert ATP hydrolysis into mechanical work to move along actin filaments.
121
What are microtubules made of?
Microtubules are polymers of the protein tubulin.
122
What is the structure of a tubulin heterodimer?
A tubulin heterodimer consists of α-tubulin and β-tubulin, each comprising 445–450 amino acids.
123
What is unique about the GTP molecule in α-tubulin?
The GTP molecule in α-tubulin is physically trapped and is never hydrolyzed or exchanged.
124
Where are α-tubulins and β-tubulins located in a microtubule?
α-tubulins are exposed at the minus end and β-tubulins are exposed at the plus end.
125
What is dynamic instability in microtubules?
Dynamic instability refers to the rapid interconversion between a growing and shrinking state of microtubules.
126
What is a catastrophe in the context of microtubules?
A catastrophe is the change from growth to shrinkage of a microtubule.
127
What happens during a rescue in microtubule dynamics?
A rescue is the change from shrinkage to growth of a microtubule.
128
What structural change occurs in protofilaments due to GTP hydrolysis?
GTP hydrolysis causes protofilaments to curve.
129
How do the rates of tubulin addition and GTP hydrolysis affect the state of microtubule ends?
If addition is faster than hydrolysis, the end remains in the T form; if slower, it transitions to the D form.
130
What is the consequence of losing the GTP cap in microtubules?
Losing the GTP cap leads to depolymerization of the microtubule.
131
What is the role of lateral contacts between protofilaments in microtubules?
Lateral contacts stabilize microtubules and contribute to their stiffness.
132
What are the two forms of microtubules based on tubulin binding?
The T form (bound to GTP) and the D form (bound to GDP).
133
What influences the dynamics of microtubules?
The binding and hydrolysis of GTP.
134
What does the term 'treadmilling' refer to in actin filaments?
Treadmilling describes the process where actin filaments maintain a constant length while adding subunits at one end and losing them at the other.
135
What leads to treadmilling of actin filaments?
Nucleoside triphosphate hydrolysis
## Footnote
Treadmilling occurs due to differences in critical concentrations and affinity for nucleotide-bound states.
136
Why do microtubules undergo dynamic instability?
Tubulin subunits with GDP bound have low affinity for one another
## Footnote
This leads to rapid depolymerization after GTP hydrolysis.
137
What is required for microtubule nucleation?
Interaction of many tubulin heterodimers and assistance from other factors
## Footnote
γ-tubulin is crucial in this process.
138
What is a microtubule-organizing center (MTOC)?
A specific intracellular location where microtubules are nucleated
## Footnote
The centrosome is a prominent example of an MTOC.
139
What is the role of γ-tubulin in microtubule nucleation?
It is involved in the nucleation of microtubule growth
## Footnote
γ-tubulin forms part of the γ-tubulin ring complex (γ-TuRC).
140
What does the centrosome consist of?
A pair of centrioles and pericentriolar material
## Footnote
The centrosome serves as a major MTOC in animal cells.
141
What happens to centrosomes during mitosis?
They duplicate and move apart to form the poles of the mitotic spindle.
142
How do microtubule arrangements vary among cell types?
Different cells have unique configurations based on their cytoskeletal requirements
## Footnote
For example, yeast have spindle pole bodies, while higher-plant cells nucleate microtubules around the nuclear envelope.
143
What is the γ-tubulin ring complex (γ-TuRC)?
A structure that aids in microtubule nucleation by providing a template for assembly.
144
What stabilizes the minus ends of microtubules in many cells?
Association with γ-TuRC or other capping proteins
## Footnote
Capping proteins like CAMSAPs protect minus ends from depolymerization and anchor them to cellular structures.
145
What are the two types of specialized processes that neurons send out?
Dendrites and axons
## Footnote
Dendrites receive electrical signals, while axons transmit them.
146
How are microtubules oriented in axons?
Minus ends pointing toward the cell body and plus ends toward the axon terminals
147
What do microtubules act as in axons?
A highway to transport proteins, vesicles, and mRNAs to axon terminals
148
What is the difference in microtubule orientation in dendrites compared to axons?
Dendrites have mixed polarities with some microtubules pointing plus ends toward the tip and others in the opposite direction
149
Name the two major classes of microtubule-based motors.
* Kinesins
* Dyneins
150
What is the primary function of kinesins?
To transport cargo such as organelles and macromolecules within the cell
## Footnote
Kinesins are crucial for long-distance transport along microtubules.
151
Which direction do most kinesins move along microtubules?
Toward the plus end of the microtubule
## Footnote
Kinesin-1 is an example of a kinesin that moves in this direction.
152
What distinguishes kinesin-13 from other kinesins?
Kinesin-13 has a central motor domain and promotes microtubule depolymerization instead of movement
## Footnote
It uses ATP energy for depolymerization.
153
What are the two branches of the dynein family?
* Cytoplasmic dyneins
* Axonemal dyneins
154
What is the function of cytoplasmic dynein 1?
To facilitate organelle and mRNA trafficking and positioning during cell migration
## Footnote
It is vital for constructing the microtubule spindle in mitosis and meiosis.
155
What is the primary role of axonemal dyneins?
To drive the beating of cilia and flagella
## Footnote
They are specialized for rapid microtubule sliding movements.
156
How do kinesins and dyneins differ structurally?
Kinesins generally have two heavy chains, while dyneins can have one to three heavy chains with various light chains
## Footnote
This structural difference correlates with their functions in cellular transport.
157
What role do kinesins play in the movement of ER membranes?
Kinesins tether ER-derived membranes to microtubule tracks and walk toward the microtubule plus ends, dragging the ER membranes into tubular protrusions.
158
What is the function of dyneins in animal cells?
Dyneins position the Golgi apparatus near the cell center by moving Golgi vesicles along microtubule tracks toward the minus ends at the centrosome.
159
How do motor proteins attach to their cargo?
Different tails and their associated light chains on specific motor proteins allow attachment to appropriate organelle cargo.
160
What is the role of dynactin in dynein transport?
Dynactin is a large protein complex that mediates dynein's attachment to cargoes and includes components that bind to microtubules and dynein.
161
How does intracellular cyclic AMP affect kinesin and dynein activity?
Increased cAMP activates kinesin, while decreased cAMP inactivates kinesin, allowing dynein to move pigment granules toward the cell center.
162
What are cilia and flagella composed of?
Cilia and flagella are built from microtubules and dynein.
163
How do bacterial flagella differ from eukaryotic flagella?
Bacterial flagella do not contain microtubules or dynein and rotate like propellers, made of the protein flagellin.
164
What are primary cilia?
Short, nonmotile counterparts of cilia and flagella that perform various cellular functions.
165
What is the main function of the axoneme in cilia and flagella?
To produce bending motion for movement.
166
What allows dynein heads to slide one microtubule doublet against the adjacent doublet?
The addition of ATP.
167
What structures generate both motile and nonmotile cilia during interphase?
Basal bodies.
168
What are the functions of centrioles?
* Assembly of the mitotic spindle in dividing cells
* Template the nucleation of the axoneme in interphase cells.
169
What transport system is required for axoneme construction?
Intraflagellar transport (IFT).
170
What functions do primary cilia serve?
They sense and respond to the exterior environment.
171
What are microtubules composed of?
Stiff polymers of tubulin molecules.
172
How do microtubules assemble?
By addition of GTP-containing tubulin subunits to the free end.
173
What characterizes the growth rates of microtubules?
The plus end grows faster than the minus end.
174
What weakens the bonds holding the microtubule together after assembly?
Hydrolysis of the bound GTP.
175
What stabilizes microtubules in cells?
Association with other structures, including microtubule-organizing centers.
176
What are microtubule-associated proteins (MAPs) responsible for?
Stabilizing microtubules.
177
What are catastrophe factors?
Proteins like kinesin-13 that act to peel apart microtubule ends.
178
What direction does dynein move along microtubules?
Toward the minus end.
179
What type of organelles are primary cilia?
Nonmotile sensory organelles.
180
What is cell polarity?
Cell polarity controls many aspects of cell function, such as the direction of protein secretion, signaling, orientation of cell division, and migration paths.
## Footnote
Cell polarity is crucial for the organization and behavior of cells.
181
How do cells polarize?
Cells polarize in response to extracellular cues or intracellular landmarks to establish specific domains on their surface.
## Footnote
This process is essential for proper cell function and development.
182
What role does the cytoskeleton play in cell polarity?
The cytoskeleton transduces polarity signals to generate whole-cell organization and behavior by building different structures at distinct cellular locations.
## Footnote
This coordination is vital for oriented cell divisions and multicellular organism development.
183
Which organisms have provided insights into the molecular basis of cell polarity?
Genetic studies in yeast, flies, and worms have provided most of our current understanding of the molecular basis of cell polarity.
## Footnote
These studies have revealed conserved mechanisms across species.
184
What are small GTPases, and how do they relate to cell polarity?
Small GTPases, such as Cdc42, Rac, and Rho, regulate the actin cytoskeleton and are critical for establishing cell polarity.
## Footnote
They act as molecular switches cycling between active and inactive states.
185
What is the function of GEFs in relation to GTPases?
Guanine nucleotide exchange factors (GEFs) activate GTPases by replacing GDP with GTP.
## Footnote
This activation is essential for the regulation of cell polarity.
186
What happens when Cdc42-GTP clusters at a site?
Cdc42-GTP clusters transmit signals that polarize the cytoskeleton and initiate the assembly of actin and septins at a single site on the mother cell.
## Footnote
This process leads to bud growth and polarized cell division.
187
What are PAR proteins, and what is their role in embryonic polarity?
PAR proteins, including Par-3, Par-6, Cdc42, and aPKC, establish anterior–posterior polarity in embryos by creating complementary cortical domains.
## Footnote
Their localization is crucial for asymmetric cell division and overall body plan determination.
188
What are the two distinct domains of epithelial cells?
Epithelial cells have an apical domain facing the outside environment and a basolateral domain facing the underlying matrix and adjacent cells.
## Footnote
These domains are crucial for the function and integrity of epithelial tissues.
189
What initiates cell polarization in epithelial cells?
Cell polarization is initiated by cues from adjacent cells or the extracellular matrix, including the formation of cell–cell junctions.
## Footnote
These junctions separate the apical and basolateral domains.
190
What are the two main domains of epithelial cells?
Apical domain and basolateral domain
## Footnote
The apical domain faces the lumen, while the basolateral domain faces the matrix and adjacent cells.
191
What initiates cell polarization in epithelial cells?
Cues from adjacent cells or the extracellular matrix
192
What is the role of microtubules in epithelial cell polarization?
They align with their minus ends anchored at the apical surface and plus ends pointing basally
193
Which proteins are identified as regulators of epithelial polarity in Drosophila?
* Cdc42
* Anterior PAR proteins
* Crumbs
* Scribble
194
What happens in the absence of PAR or Crumbs proteins?
Cells cannot form an apical domain
195
What occurs in the absence of Scribble proteins?
The apical domain is greatly expanded
196
What is the consequence of Scribble mutation in epithelial cells?
Loss of polarized cell organization and promotion of overgrowth
197
How do migrating cells differ from epithelial cells in terms of polarity?
Migrating cells display a dynamic polarity
198
What is the role of Cdc42 in cell migration?
It sets up the overall polarity of a migrating cell
199
What complex is responsible for driving protrusion at the leading edge of migrating cells?
Arp2/3 complex
200
What is the effect of Rac-GTP on actin filaments?
It stimulates the nucleation of branched actin filaments
201
What does Rho-GTP induce during cell migration?
It induces formin proteins to construct parallel actin bundles
202
What is chemotaxis?
Movement of a cell toward or away from a source of diffusible chemical
203
What do neutrophils use to detect bacterial infection?
Receptor proteins that detect N-formylated peptides
204
What is the role of phosphoinositide 3-kinases (PI3Ks) in cell migration?
They generate signaling molecules that activate Rac GTPase
205
What do nondiffusible chemical cues influence in cell migration?
Cell adhesion and directed actin polymerization
206
What is the relationship between Rac and Rho pathways during cell migration?
They are mutually antagonistic
207
What happens when the chemotactic ligand binds to its receptor?
It activates Rho and enhances myosin-based contractility
208
What family of proteins primarily regulates actin cytoskeleton and myosin contractility?
Rho family GTPases
## Footnote
Rho family GTPases are crucial for various cellular functions, particularly in cytoskeletal dynamics.
209
What can lead to defects in cell polarization and migration?
Disruption of linker proteins
## Footnote
Linker proteins connect different cytoskeletal elements, ensuring proper cell function.
210
How do microtubules contribute to cell polarity?
Support cell polarity and organize persistent movement
## Footnote
Microtubules are essential for directed movement in cells.
211
What type of proteins connect microtubule ends to actin in epithelial cells?
Cross-linking proteins
## Footnote
These proteins facilitate interaction between microtubules and actin at different cell regions.
212
Name an example of a cross-linker that binds to microtubules.
Formin proteins
## Footnote
Formin proteins also regulate actin filament assembly.
213
What role do microtubules play in directed cell migration?
Serve as a compass
## Footnote
Microtubules guide persistent movement in a specific direction.
214
How do microtubules influence actin and focal adhesions?
By serving as tracks for motor-dependent transport
## Footnote
This transport includes regulatory proteins that affect cell behavior.
215
What is required for complex, whole-cell behaviors such as migration?
Interactions among cytoplasmic filament systems and mechanical linkage to the nucleus
## Footnote
These interactions are crucial for effective cell movement.
216
What are some behaviors that directed cell migration is important for?
* Embryonic development
* Wound healing
* Tissue maintenance
* Immune system function
## Footnote
Directed cell migration is a critical process in various biological contexts.
