Lecture on Passive Transport

Introduction

• Focus on passive transport in cells.
• Example used: movement of chloride ions in the gut.

Cell Membrane Structure

• Made up of a lipid bilayer:
  • Hydrophilic heads (outer layer)
  • Hydrophobic tails (inner core)
• Structure creates a barrier for ions like chloride (Cl-).

Facilitated Diffusion

• A type of passive transport that does not require energy.
• Involves movement across a membrane without ATP.

Chloride Ion Movement

• Uses proteins embedded in the cell membrane.
• Chloride Channel:
  • Specific protein allows chloride ions to pass through.
  • Contains a pocket designed specifically for chloride ions.

Mechanism of Action

1. Chloride Binding:
   • Chloride ion binds to a specific site in the protein pocket.
   • This binding makes the protein 'uncomfortable' and initiates a change in shape.
2. Conformational Change:
   • Protein changes shape to a new conformation, facilitating ion movement.
   • The bound chloride ion moves to the intracellular space.
3. Release and Reset:
   • Chloride ion is released inside the cell.
   • Protein returns to original shape, ready to bind another chloride ion.
   • This cycle repeats without energy input, driven by the protein's desire for structural comfort.

Conclusion

• Facilitated diffusion allows chloride ions to enter the cell without energy.
• The process involves a step-wise conformational change of the channel protein to efficiently transport ions.