Membrane Fluidity

Cell Membrane

Cell Membrane (proteins and lipids) is fluid

Fluidity Regulation

Function/Purpose

• Secondary functions are dependent on fluidity
  • Transport
  • Signal transduction

Fundamentals:

• Dictated by properties of membrane lipids
  • Ordered, rigid state
  • Disordered, fluid state
• Transition temperature depends on:
  • Lenght and saturation of fatty acid chains
    • Higher C chains favor rigid state vs Low C chains
    • Saturation favors rigid state vs Unsaturation
      • Cis bonds bend the chain
      • Trans mimics saturated state
• Rapid Lateral diffusion
  • 2 micrometers in 1s
• Slow Transverse/Flip-flopping diffusion
  • Once in several hours
• Proteins attached to cytoskeleton are immobilized
• Energy barriers for protein are greater and not yet observed

Concepts:

• Higher the Tm = more fluidity
• Lower the Tm = more solid

Terminology:

• Phase Transition/Transition Temperature: melting temperature of cell membrane