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.