Actin Flashcards
(22 cards)
How does a cytoskeletal defect affect the heart?
Mutations in the actin cytoskeleton can lead to cardiomyopathies, affecting heart contraction.
How does actin impact red blood cells?
Cytoskeletal defects weaken plasma membrane support, leading to blood disorders
What role does actin play in cancer?
Metastatic cancer cells lose cytoskeletal regulation, enabling uncontrolled motility and tissue invasion.
Is actin a static or dynamic structure?
Highly dynamic, undergoing continuous polymerization and depolymerization.
How does actin contribute to cell movement?
Actin filament remodelling drives changes in shape, motility, and intracellular transport
What drug disrupts actin and stops movement?
Latrunculin A, which destroys actin filaments, halts crawling cell motility.
What is the basic building block of microfilaments?
Actin
How does actin filament polarity work?
The (+) barbed end favours monomer addition, while the (-) pointed end favours disassembly.
How do actin filaments form?
G-actin (monomers) polymerize into F-actin (filaments), forming long helical structures.
What does myosin decoration reveal about filament polarity?
Myosin S1 binding creates arrowhead-like formations, distinguishing barbed (+) vs. pointed (-) ends.
What are the three phases of actin polymerization?
1 -Nucleation Phase – Slow formation of stable actin nuclei.
2 - Elongation Phase – Rapid filament growth at both ends.
3- Steady-State Phase – Constant assembly & disassembly, maintaining filament length.
What removes the lag phase in actin polymerization?
Seeding G-actin with short filaments (nuclei) speeds up polymerization.
What is the Critical Concentration (Cc)?
The minimum G-actin concentration required for filament formation.
How do actin filaments treadmill?
ATP-actin monomers add at the (+) end, while ADP-actin dissociates at the (-) end, causing continuous filament movement.
What powers actin treadmilling?
ATP hydrolysis, triggering structural changes in actin that drive dissociation at the (-) end.
What does Cofilin do?
Binds ADP-actin at the (-) end, destabilizing filaments.
Severs actin filaments, increasing disassembly.
What is the role of Profilin?
Converts ADP-actin into ATP-actin, preparing it for assembly.
Blocks (-) end polymerization, directing monomers to the (+) end.
How does Thymosin-β4 regulate actin pools?
Sequesters ATP-G-actin, preventing premature polymerization.
Releases actin in platelets during clotting to trigger rapid filament formation
What do Capping Proteins do?
They block filament assembly & disassembly at the ends.
What does CapZ do?
Binds to the (+) barbed end, preventing monomer addition/removal.
Can be regulated by PI(4,5)P2, a plasma membrane lipid.
What is the function of Tropomodulin?
Caps the (-) pointed end, preventing actin filament breakdown.
Found in muscle cells & red blood cells for stable filament maintenance.
What does Gelsolin do?
Binds Ca²⁺, changing its structure to sever actin filaments.
Generates new (-) ends, promoting filament turnover.
