Lecture Notes: Fluid Mosaic Structure and Membrane Fluidity

Importance of Membrane Fluidity

• Membrane Fluidity: Refers to the ease with which phospholipids and proteins move within the membrane.
• Balance is Key: Essential to maintain balance to avoid too much or too little fluidity.

Problems with Membrane Fluidity

• Less Fluid Membrane:
  • Decreased permeability, making it difficult for substances to pass through.
  • Increased rigidity, leading to potential snapping under pressure.
• Too Fluid Membrane:
  • Too permeable, allowing unwanted substances to pass through easily.
  • Weak hydrophobic interactions, risking membrane disintegration.

Optimum Fluidity

• Ideal State: Phospholipids are moderately packed.
• Characteristics:
  • Partially permeable: Selectively allows substances to pass.
  • Flexible: Can bend without breaking under pressure.

Factors Affecting Membrane Fluidity

1. Temperature

• Increase in Temperature:
  • Increases kinetic energy and fluidity as phospholipids move apart.
  • Excessive temperatures can lead to membrane breakdown.
• Decrease in Temperature:
  • Reduces kinetic energy, causing tighter phospholipid packing.

2. Length of Fatty Acid Tails

• Short Tails:
  • Less tangling, allowing easier movement and increased fluidity.
• Long Tails:
  • Tangling restricts movement, decreasing fluidity.

3. Type of Fatty Acid Tails

• Saturated Fatty Acids:
  • Linear shape, leading to tightly packed phospholipids.
• Unsaturated Fatty Acids:
  • Bent shape from double bonds, increasing space and fluidity.

4. Cholesterol

• Role: Maintains membrane fluidity.
• Mechanism:
  • Prevents phospholipids from packing too closely in cold temperatures.
  • Stops phospholipids from moving too far apart in high temperatures.

Summary

• Fluidity Affected by: Temperature, fatty acid tail length, type, and cholesterol.
• Importance:
  • A membrane too fluid can break and become overly permeable.
  • A rigid membrane risks being non-permeable and snapping under pressure.
  • Fluidity must be strictly regulated for cell function.