Cell Transport Lecture Notes

Introduction

• Lecture number 8: Cell Transport
• Importance of understanding cell membrane structure and transport mechanisms.

Cell Membrane Structure

• Components of Cell Membrane:
  • Phospholipid Bilayer:
    • Composed of phospholipids, each with hydrophilic (water-loving) heads and hydrophobic (water-fearing) tails.
    • Forms a bilayer structure where heads face outward towards fluid and tails face inward.
  • Membrane Proteins:
    • Proteins embedded in the membrane (represented in purple).
    • Types include:
      • Glycoproteins: Proteins with carbohydrate chains that serve as identification markers for cells.
      • Protein Channels: Allow substances to pass in and out of the cell.
  • Cholesterol: Stabilizes the cell membrane, maintaining fluidity; mainly found in animal cells.

Overview of Cell Transport

• Types of Transport:
  • Passive Transport: No energy required. Examples:
    • Simple diffusion
    • Facilitated diffusion
    • Osmosis
  • Active Transport: Requires energy. Example:
    • Active transport mechanisms
    • Endocytosis and Exocytosis

Diffusion

• Key Concepts:
  • Solution: Mixture of substances evenly distributed.
    • Solute: Substance being dissolved (e.g., sugar).
    • Solvent: Substance doing the dissolving (e.g., water).
  • Gradient: Difference in concentration necessary for diffusion.
  • Dynamic Equilibrium: Continuous movement without net change in concentration.

Simple Diffusion

• Movement from high concentration to low concentration across the lipid bilayer.
• Some substances can pass through while others cannot.
• Factors affecting diffusion rate:
  • Concentration gradient
  • Temperature
  • Surface area
  • Distance of travel

Facilitated Diffusion

• Movement from high concentration to low concentration with help from protein channels.
• Types of Protein Channels:
  • Always open channels
  • Gated channels (open and close)
• Specific to types of molecules (e.g., glucose, ions).
• Controllable Process: Regulated by the cell.

Osmosis

• Passive movement of water through a selectively permeable membrane.
• Occurs via two processes:
  • Diffusion
  • Bulk flow through Aquaporins (specialized water channels).
• Types of Solutions:
  • Hypertonic: Higher concentration outside the cell, causing it to shrink.
  • Hypotonic: Higher concentration inside the cell, causing it to swell.
  • Isotonic: Equal concentrations inside and outside the cell, maintaining balance.
• Osmotic Pressure: Force of water pushing on cell walls; important for plant cells due to rigid cell walls.

Active Transport

• Movement from low concentration to high concentration requiring energy.
• Protein Pumps: Help transport ions against the concentration gradient.
• Maintaining ion concentrations is crucial for homeostasis.

Endocytosis and Exocytosis

• Endocytosis: Process of substances entering the cell; membrane engulfs material forming a vesicle.
• Exocytosis: Process of substances exiting the cell; vesicle merges with membrane to release content.

Conclusion

• Importance of understanding cell transport for maintaining homeostasis in living organisms.