L15: Cell Movement Flashcards
What cytoskeletal component is critical for cell migration and movement?
The actin cytoskeleton.
What is a chemoattractant?
A molecule that attracts cells, guiding their movement towards its higher concentration.
Describe the process of actin polymerisation.
Actin monomers add to the filament’s end, generating force and pushing the cell membrane forward.
What is the Arp2/3 complex?
A protein complex that assists in the nucleation of new actin filaments, helping the cell to organize actin for movement.
What role do capping proteins play in cell movement?
They stop actin polymerisation by binding to the filament end, regulating actin filament growth.
Why is actin filament recycling important in migrating cells?
Recycling maintains a supply of actin monomers for new polymerisation, crucial for continuous cell movement.
What are filopodia, and what is their function?
Thin, finger-like projections from a cell that help sense the environment and guide cell direction.
Define lamellipodia.
Broad, flat, actin-rich extensions at the front of the cell that drive the cell’s movement forward.
What are stress fibres, and what is their role in cell movement?
Actin-myosin bundles that generate tension within the cell, aiding in cellular contractility and movement.
How does the cell detach its rear to facilitate forward movement?
By breaking down adhesions at the back, allowing the cell body to follow the front as it migrates.
What are nucleation proteins, and why are they essential?
Nucleation proteins, such as the Arp2/3 complex, facilitate the rapid formation of new actin filaments at desired locations in the cell.
Explain the concept of ‘comet tails’ in cell movement studies.
In experiments with listeria bacteria, actin filaments form comet-like tails behind bacteria, demonstrating how actin polymerisation propels bacteria forward within cells.
What role does the protein ‘cofilin’ play in actin filament dynamics?
Cofilin binds to ADP-actin subunits, destabilizing and disassembling actin filaments, aiding in actin recycling.
Describe the function of profilin in actin filament turnover.
Profilin promotes the exchange of ADP for ATP on actin monomers, preparing them for reincorporation into new filaments.
What is the significance of the ATP-actin and ADP-actin forms in filament dynamics?
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.
How do filopodia and lamellipodia work together in cell migration?
Filopodia sense the environment and determine direction, while lamellipodia push the cell membrane forward, committing to movement in that direction.
What are focal adhesions, and why are they important for migrating cells?
Focal adhesions are contact points where cells attach to the substrate, anchoring the cell during migration and providing traction for forward movement.
How does myosin contribute to stress fibre function?
Myosin interacts with actin in stress fibres, generating contractile force that pulls on the cell’s cytoskeleton, aiding movement and structural integrity.
What is the main structural difference between filopodia and lamellipodia?
Filopodia consist of tight, parallel actin bundles, while lamellipodia are made of a branched, dendritic network of actin filaments.
Why is dynamic cytoskeletal regulation crucial for immune cell function?
Immune cells, such as neutrophils, rapidly change direction to pursue pathogens, requiring a flexible and responsive actin cytoskeleton.
What is the role of adhesion turnover in cell migration?
Adhesion turnover allows the cell to release rear adhesions and form new ones at the front, coordinating detachment and reattachment for forward movement.
How does actin polymerisation generate force at the cell membrane?
Actin monomers add to the filament, pushing the membrane outward and driving cell protrusions like filopodia and lamellipodia.
In what way does listeria bacteria use actin for movement within host cells?
Listeria expresses a protein that mimics an actin-binding protein, hijacking host cell actin to form a ‘comet tail’ that propels the bacteria forward.
What is a dendritic network in the context of actin structures?
A dendritic network is a branched structure formed by actin filaments, commonly found in lamellipodia, pushing the cell forward during migration.
What are the three essential requirements for actin-based motility?
1) Actin filament nucleation, 2) filament capping to regulate length, and 3) recycling of actin monomers for sustained movement.
Why is it necessary for a cell to recycle actin monomers?
Recycling conserves the finite amount of actin in the cell, enabling continuous filament turnover during active migration.
Describe the concept of ‘treadmilling’ in actin dynamics.
Treadmilling involves simultaneous addition of actin monomers at one end of the filament and removal at the other, allowing continuous filament turnover.
What triggers the switch from filopodia to lamellipodia formation in migrating cells?
Once the cell commits to a direction sensed by filopodia, it expands lamellipodia to push the cell forward in that direction.
How does the Arp2/3 complex contribute to the formation of a dendritic network?
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.
What is the role of nucleation in actin filament formation?
Nucleation is the initial step of actin filament formation, involving the assembly of actin monomers into a stable trimer to begin filament growth.
Why is the regulation of actin filament length important in cell migration?
Regulating filament length through capping proteins prevents excessive filament growth, allowing cells to control the location and timing of actin polymerisation for precise movement.
Explain the significance of actin turnover in quickly changing cellular environments.
Actin turnover allows cells to disassemble and reassemble actin filaments rapidly, enabling quick changes in movement direction and response to environmental cues.
What is the role of myosin in stress fibres?
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.
What structural characteristic of filopodia aids in environmental sensing?
Filopodia are thin, rigid, parallel bundles of actin filaments that extend from the cell, allowing it to probe and detect directional signals.
How do cells maintain the balance of actin polymerisation and depolymerisation?
Cells use regulatory proteins like cofilin for depolymerisation and profilin for ATP exchange, ensuring a balanced supply of actin monomers for continuous filament turnover.
Describe how the ‘comet tail’ phenomenon helps in studying actin dynamics.
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.
What effect does actin filament capping have on filament dynamics?
Capping halts polymerisation at the filament end, stabilizing the filament’s length and allowing precise control of cell structure and movement.
How does actin polymerisation drive membrane protrusion in migrating cells?
Actin monomers add to the filament’s barbed end, generating force that pushes the cell membrane outward, forming structures like filopodia and lamellipodia.
What are focal adhesions, and how do they assist in cell migration?
Focal adhesions are points where cells adhere to the substrate, providing anchor points and traction as the cell moves forward.
How does the structure of stress fibres contribute to cellular contraction?
Stress fibres contain actin and myosin, which interact to produce contraction, pulling parts of the cell together and generating internal tension.
Why do cells need both filopodia and lamellipodia during migration?
Filopodia provide environmental sensing, while lamellipodia are broad extensions that drive forward movement, combining to guide and push the cell.
What role does ADP-actin play in the recycling of actin filaments?
ADP-actin at the filament’s older end is targeted by cofilin, leading to disassembly and recycling of actin monomers for new polymerisation.
How does actin monomer recycling support continuous cell migration?
Recycling supplies a steady flow of actin monomers, allowing cells to maintain filament turnover and sustain movement without exhausting resources.
What is the function of VCA domain proteins in actin filament nucleation?
VCA domain proteins assist the Arp2/3 complex in recruiting actin monomers, accelerating filament nucleation and supporting rapid cell movement.
How does the cell know where to form new actin filaments?
Actin-binding proteins like the Arp2/3 complex and VCA domain proteins localize to specific areas, initiating nucleation where new filaments are needed.
What is the role of actin-binding proteins in organising different actin structures?
Actin-binding proteins regulate filament bundling, branching, capping, and disassembly, creating distinct structures like filopodia, lamellipodia, and stress fibres for various functions.
How does the leading edge of a migrating cell differ from the rear?
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.
What is the relationship between actin polymerisation and cell adhesion in movement?
Actin polymerisation pushes the cell forward, while focal adhesions secure the cell to the substrate, working together to maintain traction and direction.
