Microfilaments

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.