03_Fluidity and Membrane Proteins Flashcards
What are the three fluidity phases of biological membranes? List from least to most fluid.
solid gel< liquid-ordered “raft” < liquid-disordered
What is a liposome? Why does it form?
A liposome is a spherical bilayer with a water-filled inner compartment, two leaflets, and a hydrophilic outer surface. It is formed spontaneously by pure phospholipid bilayers to avoid free ends (where the the hydrophobic core would be otherwise exposed to an aqueous environment).
Cholesterol packs well with ________ and __________.
types of lipids; where applicable indicate saturation
sphingolipids
saturated phospholipids
What group in cholesterol faces the membrane surface?
small hydrophilic hydroxyl head group
What is the implication of the flat & rigid rings of cholesterol in the lipid bilayer?
They interfere with movement of phospholipid fatty acid tails
What are lipid rafts?
The membrane is composed of a fluid ocean of lipids with more rigid regions (microdomains – enriched with sterols and sphingolipids).
Some proteins associate with these microdomains; therefore, lipid rafts are thought to be locations for proteins to exit/enter.
Define fluidity and viscosity.
Fluidity: measure of the ease of flow
Viscosity: measure of the resistance of flow
How does temperature affect membrane fluidity?
Explain the basis.
Bilayers are more fluid at higher temperatures due to “melting” of lipid-lipid interactions.
What is the transition temperature? What does it depend on?
Tm is the temperature at which phase transition occurs.
It depends on the lipids that are present in a particular bilayer.
A membrane is (less/more) ordered at a temperature below the Tm.
more
How does the length of fatty acid acyl side chains affect the fluidity of a bilayer?
Longer chains –> less fluid bilayer
Shorter chains –> more fluid bilayer
How is the viscosity-temperature graph affected by longer acyl chains?
graph shifts to the right
at the same temperature, viscosity is greater
How does saturation affect membrane fluidity? Explain the basis.
Saturated bonds decrease fluidity
Unsaturated bonds increase fluidity.
Saturated fatty acid chains are organized more regularly. Unsaturated bonds introduce kinks into acyl chains (cis double bonds), and more room is needed to accommodate the kink. Therefore, side chains are less packed, the bilayer is more fluid.
How is Tm affected by acyl chain saturation?
Tm increases with higher degrees of acyl chain saturation.
How is the graph of viscosity-temperature affected by more unsaturation in acyl chains?
graph shifts to the left
at same temperature, viscosity is smaller
