Lecture Notes: Cell Membrane Transport

Introduction

• Comparison of cell membranes to nightclubs: selectively permeable.
• Importance of membranes in regulating what enters and exits cells.
• Substances must pass through the cell membrane, some easily, some with difficulty.

Modes of Transport

• Passive Transport

  • Does not require energy.
  • Important for moving oxygen and water across the membrane.
  • Diffusion: Movement from high to low concentration.
    • Example: People spreading out in a nightclub.
  • Osmosis: A type of diffusion specific to water through the membrane.
    • Water moves to balance concentrations (isotonic state).
    • Hypertonic: Higher concentration inside the cell.
    • Hypotonic: Lower concentration inside the cell.
    • Isotonic: Equal concentration inside and outside the cell.

• Active Transport

  • Requires energy (ATP).
  • Transports substances against their concentration gradient.
  • Example: Moving through a crowded room requires energy.
  • ATP (Adenosine Triphosphate): Energy currency of cells.

Mechanisms of Active Transport

• Sodium-Potassium Pump

  • Pumps sodium out and potassium into cells against concentration gradients.
  • Discovered by Jens Kristians Skou in the 1950s.
    • Studied nerve cells of crabs; awarded Nobel Prize.
  • Works against electrochemical gradient as well.
  • Uses ATP to change shape and transport ions.

• Vesicular Transport (Cytosis)

  • Uses vesicles to transport substances.
  • Exocytosis: Moves materials out of the cell.
    • Example: Neurotransmitter release in neurons.
  • Endocytosis: Moves materials into the cell.
    • Phagocytosis: Engulfs whole particles (e.g., white blood cells attacking bacteria).
    • Pinocytosis: Engulfs dissolved substances.
    • Receptor-mediated Endocytosis: Specific receptors for molecules (e.g., cholesterol).

Conclusion

• Review mechanisms or concepts if needed.
• Invitations to ask questions and engage on social media platforms for further clarifications.