Lecture Notes: Cell Membrane and the Fluid Mosaic Model

Key Functions of the Cell Membrane

• Protects the cell from its surroundings.
• Maintains a distinct internal environment.
• Regulates entry and exit of particles.

Components of the Cell Membrane

• Phospholipids:
  • Form a bilayer with polar, hydrophilic heads and nonpolar, hydrophobic tails.
  • Tails can be saturated or unsaturated.
• Cholesterol:
  • Maintains membrane fluidity by spacing phospholipids appropriately.
  • Prevents membrane disintegration at high temperatures and rigidity at low temperatures.
• Proteins:
  • Channel Proteins: Allow passage of large or charged molecules.
  • Carrier Proteins: Mediate active transport, e.g., sodium-potassium pump.
  • Glycoproteins: Play roles in immunity and reproduction, e.g., sperm and egg cell interaction.
  • Peripheral Proteins: Attach temporarily to the membrane, involved in processes like cellular respiration.

Permeability of the Cell Membrane

• Small Uncharged Molecules:
  • Oxygen and carbon dioxide diffuse easily due to their size and charge.
• Large or Charged Molecules:
  • Require channel or carrier proteins to pass through the membrane.

The Fluid Mosaic Model

• Describes the cell membrane as fluid and mosaic-like.
• Fluidity: Maintained by cholesterol allowing movement within the membrane.
• Mosaic Appearance:
  • Composed of various proteins and lipids arranged like a mosaic when viewed from above.

Important Processes and Examples

• Sodium-Potassium Pump: Uses ATP to move sodium out and potassium into cells.
• Cytochrome C in Mitochondria: Involved in the electron transport chain, targeted by cyanide poison.
• Glycoproteins in Reproduction: Involved in sperm-egg fusion.

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