Overview of the Cell Membrane

Function

• Regulates what comes into and out of the cell.
• Often described simply as a regulatory barrier.

Analogy

• Muskox Analogy:
  • Phospholipid Similarity:
    • Phosphate group in the head (polar, hydrophilic).
    • Lipid tail (non-polar, hydrophobic).
    • Described as amphipathic, like a muskox.
  • Heads face water (or predator); tails face away (protect the inside).

Structure

• Phospholipids:
  • Form a bilayer in the cell membrane.
  • Heads face outward towards water; tails face inward away from water.
• Fluid Mosaic Model:
  • "Fluid": Membrane components are in constant motion.
  • "Mosaic": Composed of various components.

Components

• Proteins:
  • Integral to membrane function.
  • Allow specific material to move across the membrane.
  • Types include glycoproteins (protein + sugar) and channels for ions and molecules.
• Cholesterol:
  • Maintains membrane fluidity.
  • Prevents phospholipids from packing too tightly or drifting apart excessively.

Functionality

• Phospholipids:
  • Allow small, uncharged particles (e.g. O2, CO2) to diffuse through.
  • Hydrophilic heads and hydrophobic tails create a selective barrier.
• Proteins:
  • Facilitate transport of larger or charged molecules (e.g. glucose, water through aquaporins).
  • Methods include diffusion, facilitated diffusion, and active transport.

Key Points

• Membrane fluidity is crucial for function.
• Movement through the membrane depends on molecule size and charge.
• Proteins play a vital role in determining the cell's interaction with its environment.
• The structure and function of cell membranes are consistent across all cell types.