Chapter_16_Cytoskeleton_Flashcards
What are the three main cytoskeletal elements in eukaryotic cells?
Actin filaments, microtubules, intermediate filaments.
What is the primary function of actin filaments?
Determine cell shape and facilitate movement.
Describe the process of actin filament treadmilling.
Actin monomers add at the plus end (ATP-bound) and dissociate at the minus end (ADP-bound).
What role does the ARP2/3 complex play in actin filament dynamics?
It nucleates branched actin filament structures.
How does profilin influence actin filament elongation?
It promotes actin monomer addition at the plus end.
What is dynamic instability in microtubules?
Alternation between growth and shrinkage due to GTP cap loss.
What is the structural difference between intermediate filaments and other cytoskeletal elements?
Intermediate filaments lack polarity and are made of fibrous subunits.
How does the centrosome function in microtubule organization?
It acts as the main microtubule organizing center (MTOC).
Compare the stability of intermediate filaments to actin filaments and microtubules.
Intermediate filaments are more stable and resist deformation better.
How does actin filament nucleation differ from microtubule nucleation?
Actin nucleation forms trimers, while microtubule nucleation requires γ-tubulin complexes.
What is the role of Rho family GTPases in cytoskeletal dynamics?
Regulate actin filament assembly and cell polarity.
How do small GTPases like Rac and Rho differently affect actin organization?
Rac promotes lamellipodia formation; Rho promotes stress fiber formation.
Explain the concept of ‘critical concentration’ in filament polymerization.
The concentration of subunits at which polymerization and depolymerization rates are equal.
True or False: Intermediate filaments exhibit polarity.
False.
Compare the roles of CapZ and ARP2/3 in actin filament dynamics.
CapZ caps the plus end, preventing elongation; ARP2/3 promotes branching.
True or False: Microtubules depolymerize faster at a GDP-bound end.
True.
Describe the mechanism of actin filament nucleation as shown in the diagram.
A trimer stabilizes weak interactions, allowing rapid polymerization.
How do γ-tubulin ring complexes (γ-TuRCs) contribute to microtubule nucleation?
They cap the minus end and provide a template for assembly.
What structural arrangement do intermediate filaments adopt according to the diagram?
Coiled-coils bundled laterally for mechanical strength.
What would happen to cell motility if ARP2/3 was non-functional?
Reduced lamellipodia formation, impairing migration.
How does a mutation in the tau protein affect microtubule stability in neurons?
Leads to aggregation and destabilization, associated with Alzheimer’s.
If cofilin activity is inhibited, how would it affect actin filament turnover?
Reduced disassembly at the minus end, leading to filament accumulation.
Why is dynamic instability important during mitosis?
It allows microtubules to rapidly reorganize to form the mitotic spindle.
How do motor proteins like dynein and kinesin coordinate intracellular transport?
Dynein moves cargo toward the minus end; kinesin moves cargo toward the plus end.
Predict the effect of a drug that stabilizes GDP-tubulin on microtubules.
Increases depolymerization, disrupting cytoskeletal functions.
How does filamin deficiency affect cellular movement?
Impairs actin network crosslinking, reducing cell motility.
What happens during actin-based Listeria movement?
ActA protein activates ARP2/3, propelling the bacterium forward.
How do actin filaments and microtubules cooperate during vesicle transport?
Actin facilitates local movement; microtubules manage long-distance transport.
Why are accessory proteins essential for cytoskeletal function?
They regulate filament dynamics, stability, and interactions.
True or False: Both treadmilling and dynamic instability depend on nucleotide hydrolysis.
True.
What are microtubules made of?
Tubulin heterodimers (α-tubulin and β-tubulin).
What is the primary function of intermediate filaments?
Provide mechanical strength to cells.
What motor proteins are associated with actin filaments?
Myosin.
What is the role of kinesin motor proteins?
Move cargo toward the microtubule plus end.
What is the role of dynein motor proteins?
Move cargo toward the microtubule minus end.
What cellular structure organizes microtubules?
Centrosome.
What are lamellipodia?
Sheet-like actin-rich protrusions for cell migration.
What are filopodia?
Thin, finger-like projections made of bundled actin filaments.
What is the role of GTP in microtubule dynamics?
GTP-tubulin promotes polymerization; GDP-tubulin promotes depolymerization.
What is catastrophe in microtubule dynamics?
Transition from growth to shrinkage.
What is rescue in microtubule dynamics?
Transition from shrinkage to growth.
How do thymosin and profilin regulate actin polymerization?
Thymosin prevents polymerization; profilin promotes polymerization.
How does cofilin affect actin filaments?
It severs older filaments, promoting disassembly.
What nucleates actin filaments?
ARP2/3 complex and formins.
What is the primary nucleator of microtubules?
γ-TuRC (gamma-tubulin ring complex).
Where are intermediate filaments found in epithelial cells?
Anchored to desmosomes and hemidesmosomes.
What cytoskeletal structure forms the mitotic spindle?
Microtubules.
What is the function of the nuclear lamina?
Provide structural support to the nucleus.
What accessory protein organizes actin into web-like networks?
Filamin.
What is the function of spectrin in red blood cells?
Supports the plasma membrane.
True or False: All cytoskeletal filaments are dynamic.
True.
True or False: Actin filaments can only polymerize at the plus end.
False.
True or False: Intermediate filaments require ATP or GTP for assembly.
False.
True or False: Kinesin and dynein can move along the same microtubule simultaneously.
True.
What happens if a cell lacks functional centrosomes?
Microtubule organization and mitotic spindle formation are impaired.
How would a mutation in keratin affect skin cells?
Increased fragility, leading to blistering under mechanical stress.
What effect would blocking myosin II activity have on a cell?
Impaired muscle contraction and cytokinesis.
How does a loss of filamin affect immune cells?
Reduced ability to form lamellipodia, impairing migration.
Compare microtubule and actin filament polarity.
Both have plus and minus ends; microtubules grow at the plus end faster.
How do stress fibers differ from lamellipodia?
Stress fibers are contractile bundles; lamellipodia are protrusions for movement.
Compare WASP and WAVE proteins in actin nucleation.
Both activate ARP2/3; WASP works in filopodia, WAVE in lamellipodia.
