Lecture Notes: Inside a Cell and Cell Membranes

Introduction to Cells

• Cells have various structures and organelles.
• Eukaryotic cells have membrane-bound organelles.
• Cells interact with their environment and maintain homeostasis.

Cell Membrane

• Vital for regulating what goes in and out of the cell.
• Composed of a phospholipid bilayer:
  • Polar heads and nonpolar tails.
  • Certain molecules (small, nonpolar) diffuse through easily.

Types of Transport Across Cell Membranes

Passive Transport

• Simple Diffusion:

  • Movement from high to low concentration (with the gradient).
  • No energy required.
  • Example molecules: oxygen and carbon dioxide.

• Facilitated Diffusion:

  • Involves transport proteins (channels, carriers).
  • Moves with concentration gradient, no energy required.
  • Examples: glucose transport, ions via protein channels, water via aquaporins.

Active Transport

• Movement Against Concentration Gradient:

  • From low to high concentration.
  • Requires energy (ATP).

• Sodium-Potassium Pump:

  • Example of active transport.
  • ATP energizes transport proteins.

Endocytosis and Exocytosis

• Endocytosis:

  • Bringing large molecules into the cell.
  • Types:
    • General endocytosis forms vesicles.
    • Phagocytosis: e.g., amoebas using pseudopods.
    • Receptor-mediated endocytosis: selective intake.
    • Pinocytosis: intake of fluids.

• Exocytosis:

  • Process to export materials out of the cell.
  • Used to remove waste or secrete substances.
  • Example: Exporting carbohydrates for plant cell walls.

Conclusion

• Cells have various transport mechanisms to maintain homeostasis and interact with their environment.
• Endocytosis and exocytosis play key roles in material exchange.
• Importance of ATP in active transport.