4.5 The Cytoskeleton - Biology 2e

Overview

• The cytoskeleton is a network of protein fibers within the cytoplasm.
• It helps maintain cell shape, secures organelles in place, aids in intracellular transport, and enables cellular movement.
• Consists of three types of fibers: microfilaments, intermediate filaments, and microtubules.

Microfilaments

• Narrowest of the cytoskeletal fibers (7 nm in diameter).
• Composed of two intertwined strands of actin protein.
• Functions:
  • Facilitate cellular movement.
  • Provide cell shape and rigidity.
  • Can quickly assemble/disassemble, allowing cell shape change and movement.
  • Work with myosin for muscle contraction and other cellular movements.

Intermediate Filaments

• Diameter: 8-10 nm.
• Composed of several intertwined strands of fibrous proteins.
• Function is primarily structural:
  • Support cell shape.
  • Anchor nucleus and organelles in place.
  • Include keratin, which is found in hair, nails, and skin.

Microtubules

• Largest cytoskeletal component (25 nm in diameter).
• Hollow tubes formed by polymerized dimers of alpha- and beta-tubulin.
• Functions:
  • Resist compressive forces.
  • Provide tracks for vesicle movement.
  • Involved in chromosome separation during cell division.
  • Integral to the structure of cilia, flagella, and centrioles.

Flagella and Cilia

• Both are extensions of the plasma membrane containing microtubules in a "9 + 2" array.
• Flagella:
  • Long, fewer in number.
  • Enable cell movement (e.g., sperm cells).
• Cilia:
  • Short, numerous.
  • Move substances along the cell surface (e.g., respiratory tract lining).

Comparative Structure

Key Takeaways

• The cytoskeleton is crucial for maintaining cell integrity and facilitating movement.
• Different fibers serve distinct functions but work together to support cellular activities.
• The structural arrangement of these fibers is essential for various cellular processes, including movement and division.