Lecture Notes: Plasma Membrane

Overview

• The plasma membrane of cells is primarily composed of phospholipids.
• A typical phospholipid structure comprises:
  • Phosphate group (polar, hydrophilic)
  • Glycerol molecule
  • Two fatty acid tails (nonpolar, hydrophobic)

Phospholipid Structure

• Head: Phosphate group and a trimethylammonium group.
  • Polar and hydrophilic.
  • Composed of:
    • Phosphate group
    • Two carbons
    • Trimethylammonium group (positively charged nitrogen with four methyl groups).
• Tails: Two fatty acid chains.
  • Saturated fatty acid: No double bonds.
  • Unsaturated fatty acid: Contains a double bond.
  • Nonpolar and hydrophobic.

Phospholipid Bilayer

• The cellular (plasma) membrane is made up of a phospholipid bilayer.
• Orientation:
  • Heads face aqueous environments (inside and outside the cell) due to their attraction to water.
  • Tails are oriented away from water, creating a hydrophobic interior.

Fluid Mosaic Model

• Describes the plasma membrane's structure.
• Fluidity:
  • Phospholipids and proteins can move freely (sideways, forwards, and backwards).
• Proteins in the Membrane:
  • Integral proteins: Embedded within the membrane.
  • Peripheral proteins: Extend on the exterior of the membrane.
  • Surface proteins: Lie on the surface of the membrane.

Membrane Components

• Glycoproteins: Carbohydrates attached to proteins.
• Glycolipids: Carbohydrates attached to lipids.
• Cholesterol:
  • Present in the membrane, comprising a hydroxyl group and 4 fused rings.
  • Maintains membrane fluidity:
    • Low temperatures: Acts as a spacer to increase fluidity.
    • High temperatures: Decreases fluidity by keeping phospholipids together.

Conclusion

• The plasma membrane is a complex structure essential for maintaining cellular integrity and function.
• Cholesterol plays a crucial role in regulating membrane fluidity to prevent rigidity at low temperatures and excessive fluidity at high temperatures.