Lecture on Cell Junctions and Cytoskeleton

Introduction

• The lecture covers cell junctions and their types: tight junctions, anchoring junctions, and gap junctions.
• Within anchoring junctions: desmosomes, hemidesmosomes, and adherence junctions.
• Importance of understanding cytoskeleton components as they relate to cell junctions.

Cytoskeleton Components

• Cytoskeleton: Network of protein-based filaments that provides support and structure to the cell.
  • Microtubules: Thickest filaments made of tubulin.
    • Provide support, structure, cell division, and transport of intracellular materials.
    • Form structures like cilia and flagella.
  • Microfilaments: Thinner filaments made of actin.
    • Important for muscle contraction (actin works with myosin).
    • Involved in cell division, creating cleavage during cell division.
  • Intermediate Filaments: Thickness between microtubules and microfilaments.
    • Made of keratin, resist tension, and maintain cell shape.
    • Crucial for cell junctions.

Plasma Membrane Extensions

• Cilia and Flagella:
  • Made of microtubules.
  • Cilia: Found in respiratory system and female fallopian tubes, beat rhythmically to move materials.
  • Flagella: Larger, aids in cell locomotion (e.g., sperm cells).
• Microvilli:
  • Made of microfilaments.
  • Increase surface area for absorption and secretion.

Cell Junctions

• Tight Junctions:

  • Separate cells into apical and basal portions.
  • Formed by transmembrane proteins, prevent movement of substances between cells.
  • Act as selective barriers.

• Anchoring Junctions:

  • Provide stability and flexibility.
  • Desmosomes: Patch-like structures with intermediate filaments and transmembrane glycoproteins.
  • Hemidesmosomes: Attach basal membrane to basal lamina using integrin.
  • Adherens Junctions: Use cadherin or integrin, involve actin filaments, influence cell shape and folding.

• Gap Junctions:

  • Form intracellular passageways for movement of small molecules and ions.
  • Allow electrical and metabolic coupling.
  • Formed by connexons made of connexin proteins.
  • Enable communication between adjacent cells.