Cell Structure and Plasma Membrane

Overview of Plasma Membrane

• Function:
  • Protects the interior of the cell.
  • Responsible for selective permeability (monitors materials entering and exiting the cell).

Lipid Bilayer

• Composition:
  • Made up of phospholipids, which are the primary molecules in the plasma membrane.
  • Arrangement: Two layers of phospholipids form the bilayer.

Phospholipids Characteristics

• Structure:
  • Hydrophilic (water-loving) head.
  • Hydrophobic (water-fearing) tail.
• Properties:
  • Amphipathic nature: Contains both hydrophilic and hydrophobic regions.

Function of Lipid Bilayer

• Arrangement:
  • Hydrophilic heads face watery environments both inside and outside the cell.
  • Hydrophobic tails face inward, away from water, creating a stable interior.

Selective Permeability

• Polar Molecules:

  • Cannot pass through the hydrophobic interior of the bilayer.
  • Require alternative transport means like protein channels.
    • E.g., sugars and ions use protein channels for entry.

• Nonpolar Molecules:

  • Can freely diffuse through the hydrophobic core.
  • Move from high to low concentration without resistance from the polar heads.
    • E.g., gases like oxygen and carbon dioxide.

Importance

• The bilayer's structure allows it to selectively permit molecules, maintaining the proper internal environment for cellular function.