2.4 - Plasma Membrane

Structure and Function of the Plasma Membrane

• Role of the Plasma Membrane: This membrane defines the boundary of the cell, separating it from its external environment and enabling the maintenance of a stable internal environment.

• Selective Permeability: The membrane is selectively permeable, meaning it allows certain substances to pass through more easily than others, critical for regulating entry and exit of materials.

• Fluid Mosaic Model

  • Composition: The current model of the animal cell membrane includes proteins, glycoproteins, and sterols embedded within a phospholipid bilayer, allowing for a dynamic and flexible structure.

  • Phospholipids: These are the primary components of the membrane, known for their amphipathic nature, meaning they have both hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails.

  • Bilayer Formation: Phospholipids arrange themselves in a bilayer with hydrophilic heads facing outward towards the water environments, and hydrophobic tails tucked inward, away from water.

• Membrane Fluidity

  • Role of Fatty Acids: The nature of the fatty acid tails (unsaturated or saturated) affects membrane fluidity. Unsaturated fatty acid tails, which contain double bonds, tend to increase fluidity by preventing the phospholipids from packing tightly.

  • Cholesterol's Role: Cholesterol within the bilayer also enhances membrane fluidity, contributing to the membrane's ability to function across various temperatures.