Membrane Dynamics

Question 1

Motion of phospholipid

Answer 1

Flexion (tails bump into each other)
Rotation 
Lateral diffusion (move along/swap places)
Flip flop (RARE, hydrophilic head moves through tail to other side)

Question 2

What influence does the Cis double bond have

Answer 2

Induces a kink in the tail

Reduce phospholipid packing - more fluid

Question 3

Cholesterol structure

Answer 3

Polar head (hydrophilic)
Rigid planar hydrophobic steroid ring
Flexible non polar hydrocarbon tail

Question 4

What does cholesterol do to endothermic phase of bilayer

Answer 4

Abolishes it
As temperature increases, energy inflow to bilayer is reduced/more evenly distributed
Reduces melting of bilayer

Question 5

Paradoxical effects of cholesterol on bilayer

Answer 5

Reduces phospholipid chain motion - reduces fluidity

Reduces phospholipid packing - increases fluidity

Question 6

How is cholesterol attached to phospholipid

Answer 6

Hydrogen bonding of OH in cholesterol to COOH of phospholipid

Question 7

What are lipid rafts

Answer 7

Cholesterol rich structures

• Sphingolipids with saturated FA chains
• Tightly intercalated cholesterol

Question 8

Lipid raft function

Answer 8

Scaffold for signalling molecules

Cross linking of signal receptors = higher affinity for rafts

Raft clustering can amplify signalling by bringing signalling components together

Partitioning

Question 9

Proteins within rafts

Answer 9

GPI anchored
Double acylated (intrinsic kinase activity)
alpha units of G proteins (tranducing proteins)

Question 10

Cis bond effects on bilayer

Answer 10

Reduces packing so increases fluidity

Question 11

Lipid raft - what happens here

Answer 11

Proteins can move in and out

REDUCED FLUIDITY - some proteins prefer some dont

Question 12

What is partitioning in lipid rafts?

Answer 12

changes microenvironment

makes new interactions possible - may affect their signalling