Lecture Notes: Cell Membrane Transport

Introduction

• Cells are selectively permeable like nightclubs.
• Importance of allowing necessary substances in and pushing out unnecessary ones.

Types of Membrane Transport

Passive Transport

• Diffusion: Movement of molecules from high to low concentration, requiring no energy.
  • Example: Oxygen and water move easily across cell membranes.
• Osmosis: Special kind of diffusion for water across a membrane.
  • Isotonic: Equal concentration on both sides of the membrane.
  • Hypertonic: Higher concentration outside the cell; cell loses water.
  • Hypotonic: Higher concentration inside the cell; cell absorbs water and may burst.

Active Transport

• Requires energy to move substances against concentration gradients.
• ATP (Adenosine Tri-Phosphate): Energy currency for active transport.
  • Used by transport proteins to move molecules.
• Sodium-Potassium Pump: Example of active transport, vital for brain and muscle cells.
  • Pumps sodium ions out and potassium ions in against their gradients.
  • Discovered by Jens Christian Skou in the 1950s.

Types of Active Transport

Vesicular Transport

• Uses vesicles for transport involving energy.
• Exocytosis: Transporting materials outside the cell (e.g., neurotransmitter release).
• Endocytosis: Bringing materials inside the cell.
  • Phagocytosis: Engulfing whole particles (e.g., white blood cells attacking bacteria).
  • Pinocytosis: Engulfing dissolved substances.
  • Receptor-Mediated Endocytosis: Receptors bind specific molecules, e.g., cholesterol absorption.

Conclusion

• Cell membrane transport is complex but crucial for life processes.
• Cells use a variety of mechanisms to acquire nutrients and rid of waste effectively.