9) Cell motility

• Microtubules (MTs) Summary:

  • Cytoskeletal structures
  • Composed of α and β tubulin protein subunits
  • Poymerisation of α and β tubulin provide the tracks or pathways within the cell that motor proteins can bind to non-covalently (electrostatic, hydrophobic etc)
• Microtubules (MTs) and Motor-proteins are cellular structures used for cellular movement

  
• Motor Proteins:

  • Structure: Proteins that have multiple domains for ATP Hydrolysis, Cargo-binding domain, and regulation
  • Examples: Dynein, kinesin (MT associated) actin, myosin
  • Function: Transporting vesicles, organelles, and other cargo along microtubules in a cell.
• Flagella and Cilia are motile organelles that:

  • Extend from the surface of cells
  • contain a core of microtubules
  • Are used for movement
• Cilia Summary:

  • Function: Waft fluid over a surface (eg Respiratory Tract)
  • Movement pattern: Power (fast, extended) and Recovery (Slow, Back) stroke cycle

  
• Flagella Summary:

  • Function: Propel single cells (eg: sperm, protozoa)
  • Movement Pattern: Repetitive wave motion

  
• Cilia and Flagella Structure:

  • Attached to cell by a ‘basal body’
  • Basal Body: template for motile structures and contain 9+0 array of MTs.
  • MT core (2 Central MTs surrounded by 9 Doublet MTs - 9+2 array)
  • ⤷ MTs connected by proteins that hold/bend, allowing them to slide against each other and generate movement (eg: CIlary Dynein)

  
• Ciliary Dyenin:

  • Function: Generates bending motion in cilia and flagella
  • Tail region attaches to MT in each outer doublet
  • Head region attaches to adjacent MTs
  • ⤷ Linking Proteins prevent sliding of MTs and cause structure to bend and regulate movement

  
• Actin-Dependant Cell Migration:

  Migration of cells in tissues along actin filaments.
• Migration of cells rely on:

  • Signals (eg: Chemoattractant) to stimulate chemotaxis
  • Location
  • Cell type
  • The extracellular environment
• Cell crawling is the movement of a cell along a surface using extending protrusions (eg: lamellipodia)
• Steps of Cell migration:

  1. Cell surface receptors bind to stimulus
  2. Actin polymerisation forms protrusions that are sent out by cell
  3. Protrusions adhere to surface
  4. Cell drags itself along surface
  5. Actin filaments interact with myosin II (motor proteins) and cause cell to contract
  6. Once migrated protrusions retract

  
• Actin filaments: Contraction

  • Myosin II forms filaments and use ATP to move along F-Actin
  • Myosin II heads walk towards plus end of actin
  • Actin-myosin II interactions cause actin bundles to shorten and contract
• slay yass core

  
• Methods that can be used to measure cell migration:

  1. Transwell Assay
  2. Wound healing assay
  3. TIme-lapse video microscopy