21 Questions
Which type of actin is present in non-muscle cells?
B- and γ-actin
What is the monomer of microfilaments called?
G-actin
What do actin monomers assemble to form?
Filamentous actin (F-actin)
How do two protofilaments form a microfilament?
They twist around each other
How are microfilaments polarized?
With fast plus end and slow minus end
What regulates the assembly, growing, or shortening of microfilaments?
ATP binding and hydrolysis
What happens to ATP bound to G-actin after microfilament assembly?
It is hydrolyzed
What results in a difference in the critical concentration of monomers needed for polymerization at the two ends of microfilaments?
Hydrolysis of ATP
In in vitro conditions, what do microfilaments assembly share the same features with?
Assembly of microtubules
Where does the nucleation of microfilaments (MFs) most frequently occur?
At or near the plasma membrane
What is the function of actin-bundling proteins?
Mediate the tight packing of MFs into parallel arrays
What are the finger-like extensions formed by bundles of actin filaments called?
Microvilli
What is the main function of pseudopodia?
Actin-filled three-dimensional projections important for phagocytosis
What is the function of myosin molecular motors in cell movement?
Important for protrusion and traction of the cell
Where are lamellipodia and filopodia located?
On the cell surface
What is the function of actin networks?
Loosely crosslink MFs in orthogonal arrays to form a three-dimensional meshwork
What is the main function of microvilli in the small intestine?
Increase the cell's surface area for greater absorptive capacity
What is the role of adhesion plaque in cell movement?
Mediate the connection of MFs across the plasma membrane to the substratum
What are the structures formed by tightly packed MFs into parallel arrays called?
Actin bundles
What is the main function of filopodia?
Important for crawling movement of the cell
What is the function of actin-binding proteins?
Regulate MF assembly and disassembly, serve as nucleation sites, and stimulate addition of actin monomers into filaments
Study Notes
Actin in Non-Muscle Cells
- Non-muscle cells contain β-actin, the most common form of actin.
Microfilaments
- Actin monomers are called G-actin.
- G-actin monomers assemble to form F-actin, a polymer.
- Two protofilaments twist together to form a microfilament.
- Microfilaments are polarized, with a plus end and a minus end.
- The assembly, growth, and shortening of microfilaments are regulated by various factors, including ATP, ions, and actin-binding proteins.
Microfilament Assembly
- ATP bound to G-actin is hydrolyzed to ADP after microfilament assembly.
- A difference in critical concentration of monomers at the two ends of microfilaments results from the difference in ATP-ADP exchange rates.
In Vitro Conditions
- In vitro microfilament assembly shares the same features with in vivo conditions.
Microfilament Nucleation
- Microfilament nucleation most frequently occurs at the cell membrane.
Actin-Bundling Proteins
- Actin-bundling proteins bind to actin filaments and bundle them together.
Pseudopodia
- Finger-like extensions formed by bundles of actin filaments are called pseudopodia.
- The main function of pseudopodia is to sense the environment and facilitate cell movement.
Myosin Molecular Motors
- Myosin molecular motors use ATP hydrolysis to move along actin filaments, contributing to cell movement.
Lamellipodia and Filopodia
- Lamellipodia and filopodia are located at the leading edge of migrating cells.
- They are involved in cell migration and sensing the environment.
Actin Networks
- Actin networks provide mechanical support and shape to cells.
Microvilli
- The main function of microvilli in the small intestine is to increase the surface area for absorption.
Adhesion Plaque
- Adhesion plaques are specialized structures that connect the actin cytoskeleton to the extracellular matrix, facilitating cell movement.
Actin-Binding Proteins
- Actin-binding proteins regulate the dynamics and organization of actin filaments.
Stress Fibers
- Tightly packed microfilaments into parallel arrays are called stress fibers.
- They provide mechanical support and resist external forces.
Filopodia
- The main function of filopodia is to sense the environment and guide cell movement.
Test your knowledge of microfilaments with this quiz! Learn about the thinnest fibers of the cytoskeleton, the types of actin, and the structure of the actin molecule. Perfect for biology enthusiasts and students studying cell biology.
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