L15: Cell Movement

Question 1

What cytoskeletal component is critical for cell migration and movement?

Answer 1

The actin cytoskeleton.

Question 2

What is a chemoattractant?

Answer 2

A molecule that attracts cells, guiding their movement towards its higher concentration.

Question 3

Describe the process of actin polymerisation.

Answer 3

Actin monomers add to the filament’s end, generating force and pushing the cell membrane forward.

Question 4

What is the Arp2/3 complex?

Answer 4

A protein complex that assists in the nucleation of new actin filaments, helping the cell to organize actin for movement.

Question 5

What role do capping proteins play in cell movement?

Answer 5

They stop actin polymerisation by binding to the filament end, regulating actin filament growth.

Question 6

Why is actin filament recycling important in migrating cells?

Answer 6

Recycling maintains a supply of actin monomers for new polymerisation, crucial for continuous cell movement.

Question 7

What are filopodia, and what is their function?

Answer 7

Thin, finger-like projections from a cell that help sense the environment and guide cell direction.

Question 8

Define lamellipodia.

Answer 8

Broad, flat, actin-rich extensions at the front of the cell that drive the cell’s movement forward.

Question 9

What are stress fibres, and what is their role in cell movement?

Answer 9

Actin-myosin bundles that generate tension within the cell, aiding in cellular contractility and movement.

Question 10

How does the cell detach its rear to facilitate forward movement?

Answer 10

By breaking down adhesions at the back, allowing the cell body to follow the front as it migrates.

Question 11

What are nucleation proteins, and why are they essential?

Answer 11

Nucleation proteins, such as the Arp2/3 complex, facilitate the rapid formation of new actin filaments at desired locations in the cell.

Question 12

Explain the concept of ‘comet tails’ in cell movement studies.

Answer 12

In experiments with listeria bacteria, actin filaments form comet-like tails behind bacteria, demonstrating how actin polymerisation propels bacteria forward within cells.

Question 13

What role does the protein ‘cofilin’ play in actin filament dynamics?

Answer 13

Cofilin binds to ADP-actin subunits, destabilizing and disassembling actin filaments, aiding in actin recycling.

Question 14

Describe the function of profilin in actin filament turnover.

Answer 14

Profilin promotes the exchange of ADP for ATP on actin monomers, preparing them for reincorporation into new filaments.

Question 15

What is the significance of the ATP-actin and ADP-actin forms in filament dynamics?

Answer 15

ATP-actin adds to the growing end of the filament, while ADP-actin, prone to disassembly, assists in recycling actin at the filament’s older regions.

Question 16

How do filopodia and lamellipodia work together in cell migration?

Answer 16

Filopodia sense the environment and determine direction, while lamellipodia push the cell membrane forward, committing to movement in that direction.

Question 17

What are focal adhesions, and why are they important for migrating cells?

Answer 17

Focal adhesions are contact points where cells attach to the substrate, anchoring the cell during migration and providing traction for forward movement.

Question 18

How does myosin contribute to stress fibre function?

Answer 18

Myosin interacts with actin in stress fibres, generating contractile force that pulls on the cell’s cytoskeleton, aiding movement and structural integrity.

Question 19

What is the main structural difference between filopodia and lamellipodia?

Answer 19

Filopodia consist of tight, parallel actin bundles, while lamellipodia are made of a branched, dendritic network of actin filaments.

Question 20

Why is dynamic cytoskeletal regulation crucial for immune cell function?

Answer 20

Immune cells, such as neutrophils, rapidly change direction to pursue pathogens, requiring a flexible and responsive actin cytoskeleton.

Question 21

What is the role of adhesion turnover in cell migration?

Answer 21

Adhesion turnover allows the cell to release rear adhesions and form new ones at the front, coordinating detachment and reattachment for forward movement.

Question 22

How does actin polymerisation generate force at the cell membrane?

Answer 22

Actin monomers add to the filament, pushing the membrane outward and driving cell protrusions like filopodia and lamellipodia.

Question 23

In what way does listeria bacteria use actin for movement within host cells?

Answer 23

Listeria expresses a protein that mimics an actin-binding protein, hijacking host cell actin to form a ‘comet tail’ that propels the bacteria forward.

Question 24

What is a dendritic network in the context of actin structures?

Answer 24

A dendritic network is a branched structure formed by actin filaments, commonly found in lamellipodia, pushing the cell forward during migration.

Question 25

What are the three essential requirements for actin-based motility?

Answer 25

1) Actin filament nucleation, 2) filament capping to regulate length, and 3) recycling of actin monomers for sustained movement.

Question 26

Why is it necessary for a cell to recycle actin monomers?

Answer 26

Recycling conserves the finite amount of actin in the cell, enabling continuous filament turnover during active migration.

Question 27

Describe the concept of ‘treadmilling’ in actin dynamics.

Answer 27

Treadmilling involves simultaneous addition of actin monomers at one end of the filament and removal at the other, allowing continuous filament turnover.

Question 28

What triggers the switch from filopodia to lamellipodia formation in migrating cells?

Answer 28

Once the cell commits to a direction sensed by filopodia, it expands lamellipodia to push the cell forward in that direction.

Question 29

How does the Arp2/3 complex contribute to the formation of a dendritic network?

Answer 29

The Arp2/3 complex binds to the side of existing actin filaments, creating branch points for new filament growth, forming a dense, branched network in structures like lamellipodia.

Question 30

What is the role of nucleation in actin filament formation?

Answer 30

Nucleation is the initial step of actin filament formation, involving the assembly of actin monomers into a stable trimer to begin filament growth.

Question 31

Why is the regulation of actin filament length important in cell migration?

Answer 31

Regulating filament length through capping proteins prevents excessive filament growth, allowing cells to control the location and timing of actin polymerisation for precise movement.

Question 32

Explain the significance of actin turnover in quickly changing cellular environments.

Answer 32

Actin turnover allows cells to disassemble and reassemble actin filaments rapidly, enabling quick changes in movement direction and response to environmental cues.

Question 33

What is the role of myosin in stress fibres?

Answer 33

Myosin interacts with actin within stress fibres to generate contractile forces that pull different parts of the cell together, aiding in movement and shape maintenance.

Question 34

What structural characteristic of filopodia aids in environmental sensing?

Answer 34

Filopodia are thin, rigid, parallel bundles of actin filaments that extend from the cell, allowing it to probe and detect directional signals.

Question 35

How do cells maintain the balance of actin polymerisation and depolymerisation?

Answer 35

Cells use regulatory proteins like cofilin for depolymerisation and profilin for ATP exchange, ensuring a balanced supply of actin monomers for continuous filament turnover.

Question 36

Describe how the ‘comet tail’ phenomenon helps in studying actin dynamics.

Answer 36

The ‘comet tail’ observed in bacteria like listeria highlights how actin polymerisation at one end pushes bacteria forward, serving as a model for understanding cell motility mechanisms.

Question 37

What effect does actin filament capping have on filament dynamics?

Answer 37

Capping halts polymerisation at the filament end, stabilizing the filament’s length and allowing precise control of cell structure and movement.

Question 38

How does actin polymerisation drive membrane protrusion in migrating cells?

Answer 38

Actin monomers add to the filament’s barbed end, generating force that pushes the cell membrane outward, forming structures like filopodia and lamellipodia.

Question 39

What are focal adhesions, and how do they assist in cell migration?

Answer 39

Focal adhesions are points where cells adhere to the substrate, providing anchor points and traction as the cell moves forward.

Question 40

How does the structure of stress fibres contribute to cellular contraction?

Answer 40

Stress fibres contain actin and myosin, which interact to produce contraction, pulling parts of the cell together and generating internal tension.

Question 41

Why do cells need both filopodia and lamellipodia during migration?

Answer 41

Filopodia provide environmental sensing, while lamellipodia are broad extensions that drive forward movement, combining to guide and push the cell.

Question 42

What role does ADP-actin play in the recycling of actin filaments?

Answer 42

ADP-actin at the filament’s older end is targeted by cofilin, leading to disassembly and recycling of actin monomers for new polymerisation.

Question 43

How does actin monomer recycling support continuous cell migration?

Answer 43

Recycling supplies a steady flow of actin monomers, allowing cells to maintain filament turnover and sustain movement without exhausting resources.

Question 44

What is the function of VCA domain proteins in actin filament nucleation?

Answer 44

VCA domain proteins assist the Arp2/3 complex in recruiting actin monomers, accelerating filament nucleation and supporting rapid cell movement.

Question 45

How does the cell know where to form new actin filaments?

Answer 45

Actin-binding proteins like the Arp2/3 complex and VCA domain proteins localize to specific areas, initiating nucleation where new filaments are needed.

Question 46

What is the role of actin-binding proteins in organising different actin structures?

Answer 46

Actin-binding proteins regulate filament bundling, branching, capping, and disassembly, creating distinct structures like filopodia, lamellipodia, and stress fibres for various functions.

Question 47

How does the leading edge of a migrating cell differ from the rear?

Answer 47

The leading edge contains actin polymerisation driving forward movement, while the rear has stress fibres and focal adhesions that pull the cell body and release attachments.

Question 48

What is the relationship between actin polymerisation and cell adhesion in movement?

Answer 48

Actin polymerisation pushes the cell forward, while focal adhesions secure the cell to the substrate, working together to maintain traction and direction.