Actin filaments

Definition

Actin filaments, also known as microfilaments, are thin protein fibers made of actin monomers that play a crucial role in various cellular processes, including motility, shape maintenance, and division. They are part of the cytoskeleton, providing structural support and enabling cellular movements by interacting with myosin and other motor proteins. Their dynamic nature allows them to rapidly grow and shrink, facilitating changes in cell shape and movement.

5 Must Know Facts For Your Next Test

1. Actin filaments are approximately 7 nm in diameter and are among the smallest components of the cytoskeleton.
2. They can rapidly polymerize and depolymerize, allowing cells to respond quickly to changes in their environment.
3. Actin filaments are involved in various types of cell movement, including amoeboid movement, muscle contraction, and cytokinesis during cell division.
4. They form structures like stress fibers, lamellipodia, and filopodia that are essential for maintaining cell shape and enabling motility.
5. Regulatory proteins like profilin and cofilin control the dynamics of actin filament assembly and disassembly.

Review Questions

• How do actin filaments contribute to cell motility and the function of molecular motors?
  • Actin filaments serve as tracks for molecular motors like myosin, enabling various forms of cell movement. Myosin walks along actin filaments, pulling on them to generate tension and contractile forces that lead to muscle contraction or other movements such as cytokinesis. The dynamic nature of actin allows for rapid reorganization during processes like cell migration, where structures such as lamellipodia extend and retract based on cellular signaling.
• Discuss the role of actin dynamics in the context of cell shape maintenance and changes during motility.
  • Actin dynamics are critical for maintaining cell shape and enabling motility by allowing cells to rapidly reorganize their cytoskeletal structure. When a cell receives signals to migrate, actin filaments rapidly polymerize at the leading edge to form protrusions like lamellipodia. Concurrently, actin depolymerizes at the rear, allowing the cell to pull itself forward. This coordinated assembly and disassembly of actin filaments are essential for effective movement while ensuring the overall integrity of the cell's structure.
• Evaluate how regulatory proteins influence actin filament dynamics and the implications for cellular functions.
  • Regulatory proteins significantly influence actin filament dynamics by controlling both polymerization and depolymerization rates. For instance, profilin promotes actin monomer addition to growing filaments, while cofilin enhances disassembly by severing existing filaments. The balance between these activities is crucial for cellular functions like division and migration. Disruptions in these regulatory pathways can lead to diseases such as cancer, where altered motility contributes to metastasis.

Related terms

Myosin: A type of motor protein that interacts with actin filaments to produce muscle contraction and other forms of cellular movement.

Cytoskeleton:

A network of protein filaments and tubules in the cytoplasm that gives cells their shape, offers mechanical support, and facilitates movement.

Lamellipodia: Flat, sheet-like extensions of the cell membrane filled with actin filaments, important for cell migration.