Lecture Notes: Cell Membranes and the Fluid Mosaic Model

Introduction

• Background Noise: Fireworks are happening due to Independence Day.
• Focus of Lecture: Understanding cell membranes using electron micrographs and the fluid mosaic model.

Electron Microscopy

• Transmission Electron Micrograph:
  • Despite 0.2 nm resolution, details of cell surface membrane are limited.
  • Appears as a single line with insufficient information.
• Scanning Electron Micrograph:
  • Shows cell surface membrane in 3D.
  • Cannot see inside of the cell.
• Issue: Limited detail visible; need to describe the cell surface membrane composition.

The Fluid Mosaic Model

• Proposed by: Seymour Jonathan Singer and Garth L. Nicolson in 1972.
• Purpose: To describe the structure of the cell membrane.

Mosaic Component

• Definition of Mosaic:
  • Art form using small, closely packed pieces to form an image or pattern.
  • Membrane is made up of many phospholipids and proteins.
  • Proteins appear as purple structures in diagrams.
• Membrane Composition:
  • Phospholipids and proteins are randomly scattered.
  • View from the top shows phosphate heads and protein molecules, not the tails.

Fluid Component

• Fluidity Concept:
  • Proteins and phospholipids are free to move around.
  • Membrane is dynamic, not rigidly packed.
• Illustration:
  • Phospholipids with pink and green heads can switch positions.
  • Proteins move as well, demonstrating a dynamic structure.
• Analogy: Plastic balls in a pool representing phospholipids and proteins moving freely.

Importance of the Fluid Mosaic Model

• Visualization: Helps conceptualize the cell membrane structure despite limitations of microscopy.
• Function: Explains the flexibility and dynamic nature of cell membranes, allowing for movement and reorganization of molecules.

Conclusion

• Revisiting Micrographs:
  • Cross-section diagrams show phospholipid bilayer as two lines.
  • Though fatty acid tails and proteins are not visible, model helps infer their presence.
• Model Utility: Essential for imagining the cell surface membrane's structure and function beyond what can be visually captured.