bio 2.5

  • Introduction

    • Topic of discussion: Membrane Permeability
    • Key areas:
    • Structure of the cell membrane
    • Selective permeability
    • Fluid mosaic model
    • Molecule transport across the membrane
    • Role of cell walls

  • Cell Membrane Structure

    • Composed of phospholipids:
    • Amphipathic nature: hydrophobic (water-repelling) and hydrophilic (water-attracting) properties.
    • Formation: Spontaneously form a bilayer in aqueous solutions.
    • Fluid Mosaic Model: Dynamic structure, includes:
    • Proteins
    • Steroids
    • Carbohydrates

  • Selective Permeability

    • Direct result of membrane structure.
    • Freely passing molecules:
    • Small non-polar molecules:
      • Examples: ext{N}2 (Nitrogen), ext{O}2 (Oxygen), ext{CO}_2 (Carbon Dioxide)
    • Molecules needing assistance:
    • Large polar molecules and ions (hydrophilic substances) cannot freely cross.
    • Require transport proteins:
      • Channel proteins:
      • Hydrophilic tunnels that span the membrane for target molecules.
      • Carrier proteins:
      • Change shape to move target molecules from one side of the membrane to the other.
    • Small polar molecules (like water):
    • Can pass but only in minimal amounts.

  • Cell Walls

    • Function: Provide a structural boundary and permeable barrier.
    • Structural boundary:
    • Protects and maintains cell shape.
    • Prevents rupture under high internal water pressure.
    • Supports against gravity.
    • Permeable barrier:
    • Allows transfer of nutrients, waste, and ions through structures called Plasmodesmata in plant cells.
    • Composition:
    • Found in:
      • Plants: Composed of cellulose (a polysaccharide).
      • Fungi: Made of chitin (another polysaccharide).
      • Prokaryotes: Composed of peptidoglycan (a polymer of sugars and amino acids).

  • Key Takeaways

    • The structure of the cell membrane results in selective permeability.
    • Small non-polar molecules can pass freely; hydrophilic substances need transport proteins.
    • The cell wall offers structural integrity and a permeability barrier.
    • Cell walls in plants, fungi, and prokaryotes are comprised of complex carbohydrates.

  • Practice and Application

    • Skills focus on using data to evaluate hypotheses.
    • Discussion of treatment groups and evaluating the reliability of estimates based on provided data.

  • Conclusion

    • Understanding membrane permeability is crucial for cell functionality and structure.
    • Insight into different types of molecules' movement across membranes enhances comprehension of cellular processes.