Chapter 17A

Actin and Tubulin in the Cytoskeleton

  • Structured components of the cytoskeleton include:
    • Actin
    • Tubulin
  • Size references:
    • Typical diameter: 10 μm
  • Source: Essential Cell Biology © Garland Science 2010

Kinesin Superfamily

  • Overview: The kinesin superfamily comprises 45 genes categorized into 14 gene families.
    • Notable members include:
    • kinesin-1
    • kinesin-5
    • kinesin-13
    • kinesin-14
  • Motor Domain: All kinesins share an identical motor head domain comprised of approximately 500 amino acids.
  • Source: Molecular Biology of the Cell 6e © Garland Science 2015

Structure of Kinesin

  • Electron Microscopy: Provides visualization of kinesin motors and their characteristics.
  • Size reference: Each kinesin motor is approximately 10 nm in diameter.
  • Source: Molecular Biology of the Cell © Garland Science 2008

Kinesin Functionality

  • Direction of Movement:
    • Kinesin motors primarily "walk" toward the (+) end of microtubules (MTs).
    • The process of movement involves:
    • Hydrolyzing 1 ATP for each 8 nm step.
    • Mechanism: One ATP allows travel of 8 nm across microtubule.
    • Cargo attachment:
    • Cargo is bound to the "tail" domains of kinesin.
    • Movement resembles a ball-and-chain mechanism.

Bidirectional Movement of Cargo

  • Motor Protein Requirement: Bidirectional cargo transport along microtubules necessitates both kinesin and dynein as motor proteins.
    • Kinesin moves cargo toward the (+) end of microtubule.
    • Dynein moves cargo toward the (-) end of microtubule.
  • Source: Essential Cell Biology © Garland Science 2010

Dynein

  • Types of Dynein: Different types include:
    • Cytoplasmic dynein
    • Ciliary dynein
  • Structural Composition:
    • Dynein dimers consist of 2 catalytic cores, over which motor heads operate.
  • Movement involves:
    • Cargo tethered to dynein is moved toward centrosomes.
  • Size reference: Dynein motors exhibit 25 nm movement.
  • Source: Molecular Biology of the Cell 6e © Garland Science 2015

Ciliary and Flagellar Movement

  • Mechanisms: Cilia beat in coordinated sweeps, essential for functions like clearing airways.
  • The movement is described as:
    • Power stroke executed by cilia requiring synchronized activity.
    • Rhythmic flexion of axoneme is driven by ciliary dynein motors.
  • Source: Essential Cell Biology © Garland Science 2010

Centriole Structure and Function

  • Centriole Composition:
    • Comprised of microtubule triplets, usually grouped in pairs.
    • Each centriole encases several protofilament structures: 13 in a circular formation.
  • Role: Crucial for centrosome formation and subsequent cellular functions such as flagella and cilia biosynthesis.
  • Source: Various notes from Molecular Biology of the Cell.

Primary Cilium

  • Description: A specialized single cilium found in most differentiated cells, acting as a sensory organelle.
  • Composition includes:
    • Basal body forming the foundation connected to the plasma membrane.
  • Size reference: Primarily cilium dimensions approximate 200 nm.

Motor Proteins in Cellular Motion

  • Discussed in terms of:
    • Mechanisms such as dynein dimers and trimers for different cellular functions.
    • Nomenclature in dynein movements indicates the utilization of energy derived from ATP hydrolysis.
  • Key Features include:
    • Mechanistic details of dynein causing MT sliding vs. bending explained via mechanical and chemical interactions.
  • Detailed movement protocols for the axoneme and flagellar structures.

Microtubule Organization

  • Architecture: "9 + 2" arrangement of microtubules in ciliary axoneme.
  • Components include:
    • Radial spokes
    • Inner/outer dynein arms
    • Structure related to coordinated movement and functionality.

Spindle Complex Dynamics

  • Spindle complexes are vital for the capture and segregation of sister chromatids during cell division.
  • Key dynamics include:
    • Interactions among astral and kinetochore microtubules.
    • Role of motor proteins in ensuring even distribution to the cell poles described in detail (e.g., pulling forces, ATP hydrolysis).
  • Source: Molecular Biology of the Cell © Garland Science 2008