The Membrane Bilayer: Dynamics

Question 1

how can lipids move in the bilayer

Answer 1

flexion: wobbling of tails
rotation
lateral diffusion
flip flop-very rare. gains enough energy to get the hydrophilic head grp through the hydrophobic part of the membrane & out on the there side

Question 2

what happens if there is a cis double bond in the phospholipid molecule

Answer 2

introduces a kink
effectively kicks out the leg of the fatty acid on the phospholipid
increases fluidity of membrane by decreasing packing

Question 3

why is a source of polyunsaturated fat very important

Answer 3

cis double bonds further down the chain can’t be made in the body so have to be provided by diet.
they introduce a kink so reduce phospholipid packing. this provides more opportunity for movement allowing proteins in membrane to undergo conformational changes

Question 4

how does cholesterol insert into phospholipid bilayer

Answer 4

cholesterol sits next to phospholipids.
hydroxyl group of cholesterol forms h.bond with carbonyl of carboxylic acid grp of fatty acid on phospholipid.
this locks cholesterol onto adjacent phospholipid

Question 5

paradoxical effect of cholesterol in phospholipid bilayers

Answer 5

reduced phospholipid packing, increased fluidity

reduced phospholipid chain motion, reduced fluidity

Question 6

what are lipid rafts and what is their function

Answer 6

congregation of particular lipid types (cholesterol and sphingolipids) result in the formation of lipid rafts that have a reduced mobility compared to the rest of the membrane and also host specific proteins.
act as a region within the membrane where signalling molecules can scaffold together to make transfer of info efficient.
reduced mobility of the rafts optimises signalling stability, keeping components of the signalling pathway close together limiting ‘random drift’