OBJ - Lipids & Membranes

Question 1

Describe the common features of biological membranes according to the Fluid Mosaic Model of Singer and Nicoloson; both the generalizations & exceptions

Answer 1

• Valid generalizations:
  
  • lipid bilayer is the strucutral matrix of the membrane with many proteins embedded in the bilayer
  • bilayer is viscous & 2D fluid
• Exceptions to generalizations:
  
  • bilayer varies in thickness & composition
  • lipids & proteins can diffuse laterally across the membrane
    
    • Protein catalyst needed to flip flop

Question 2

Define and describe membrane fusion

Answer 2

Bilayers don’t fuse spontaneously - need proteins to activate & has to be in vivo

Question 3

Categorize the types of proteins associated with membranes and correlate the different types of interaction with protein structure

Answer 3

• Intrinsic/integral = runs through the bilayer/embedded
• Extrinsic/peripheral = attached to one surface of bilayer
• Lipid linked = covalently attached
• Bilayer thickness & asymmetry alters protein confirmation
  
  • Changes in bilayer can change protein’s confirmation to activate/deactivate

Question 4

Define and discuss lipid polymorphism

Answer 4

Def: he behaviour of lipids that influences their long-range order, i.e. how they aggregate (i.e. bilayer or micelle)

=> Liposomes

Want the most energetically favorable: bilayer sheets whose hydrophobic edges self-seal

Question 5

Discuss the factors that control membrane fluidity

Answer 5

• Cells adjust FA composition, head groups & cholesterol composition to alter gel phase (“homoviscous adaptation”)
  
  • why Fish & plants (cold enviornments have lots of Polyunsat Fats)
• Cholesterols primarilty modulate membrane fluidity -> viscocity of EVOO
• Cholesterol packs/snuggles in nicely with C chaings b/c bond angles are very similar to the chair conformation of the 4 carbon rings
  
  • Increase in cholesterol = increase in fluidity b/c decreases “gel point” (membrane analogous to freezing point, where it solidifies