Notes on Cell Membranes

Overview

• All cells are surrounded by a membrane, similar to how skin covers the body.
• This membrane is known as the plasma membrane.
• It acts as a barrier that regulates entry and exit of substances, making it semi-permeable (selectively permeable).

Structure of the Plasma Membrane

Phospholipid Bilayer

• Composed mainly of phospholipids.
• Phospholipid Structure:
  • Head: Made of phosphate, hydrophilic (water-loving).
  • Tails: Two fatty acid tails, hydrophobic (water-fearing).
• Forms two layers (bilayer):
  • Hydrophobic tails face each other.
  • Hydrophilic heads face the watery environment and cytoplasm.
• The bilayer is responsible for the membrane's semi-permeability:
  • Smaller, less charged particles pass easily.
  • Larger, more charged particles struggle to pass.

Other Membrane Components

1. Cholesterol
   • Stabilizes the membrane.
   • Important for controlling permeability despite its negative connotation.
2. Proteins
   • Involved in various functions, especially in transporting materials across the membrane.
3. Carbohydrates
   • Often involved in cell identification.
   • Blood types result from carbohydrates on proteins, helping distinguish between self and foreign cells.

Conclusion

• The plasma membrane is crucial for all life, providing a barrier that allows for necessary regulation.
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