The Membrane Bilayer: structure and dynamic

Question 1

Membrane Composition

Answer 1

Varies with source of membranse

• 40% lipid
• 60% protein
• 1-10% carbs

hydrated structures 20% water

Question 2

Whar are amphipathic molecules?

Answer 2

they contain both a hydrophillic and hydrophobic group

Question 3

Glycolipids

Answer 3

sugar containing lipids

• cerebrosides- head group sugar monomer
• gangliosides- head group oligosaccharide (sugar multimers)

Question 4

What are liposomes?

Answer 4

if we take phospholipids and sonicate it in an aqueous environment, it will form enclosed environments of liposomes

Question 5

In what ways can a phospholipid move?

Answer 5

flexion- tails vibrate which causes them to bump into each other- allows lateral diffusion

Rotation- they can change places which allows lateral diffusion

Flip flop- can get the hydrophilic head through hydrophobic part of bilayer - rare

lateral diffusion

Question 6

Cholesterol structure

Answer 6

Polar head group
rigid planar steroid ring structure
non-polar hydrocarbon tail
solid

Question 7

Paradoxial effect of cholesterol

Answer 7

reduced fluidity and mobility of phospholipid chain

increased fluidity as reduced phosphlipid packing as cholesterol is there

Question 8

What are lipid rafts?

Answer 8

dynamic cholesterol rich structures

comprised of

• sphingolipids with saturated fatty acid chains
• tightly intercalated cholesterol

can include or exclude membrane proteins

affinity of raft to protein regulated by stimuli
proteins can move in and out

Question 9

Lipid rafts function

Answer 9

scaffold proteins involved in signal transduction

if a number of proteins are needed to be together to transmit a signal to the outside of the cell, the raft acts as a region within the membrane where the proteins can scaffold together rather than searching for each other

Question 10

What does crosslinking of signalling receptors do?

Answer 10

increase their affinity for rafts

Question 11

What does raft clustering do?

Answer 11

amplify signalling by bringing signalling components together

Question 12

What ways can proteins move in the bilayer

Answer 12

Conformational change
Rotational
Lateral
No flip flop