2. Membrane Bilayer

Question 1

What are the 5 general functions of the membrane bilayer?

Answer 1

Continuous, highly selective permeability barrier
Control of enclosed chemical environment
Communication
Recognition - signalling molecules
Signal generation in response to stimuli

Question 2

Describe the membrane composition

Answer 2

Dry weight: 40% lipid, 60% protein, 1-10% carbohydrate

20% of total weight is water

Question 3

What are amphipathic molecules?

Answer 3

Contain both hydrophilic and hydrophobic moiety

Question 4

Describe the structure of a phospholipid

Answer 4

Head groups - range of polar head groups e.g. choline, amines, amino acids, sugar
Fatty acid chains - between 14-16C length, cis double bond introduces kink

Question 5

What are glycolipids?

Answer 5

Sugar containing lipids
Cerebrosides - head group sugar monomer
Ganglioside - head group oligosaccharide

Question 6

How can phospholipids move within the membrane?

Answer 6

Flex (spread out)
Rotate
Move laterally
Flip flop (rare)

Question 7

What do cis outlets bonds do?

Answer 7

Reduce phospholipid packing

Question 8

Describe the structure of cholesterol

Answer 8

Polar head group due to -OH
Rigid planar steroid ring structure
Non-polar hydrocarbon chain

Question 9

What is the role of cholesterol in the membrane?

Answer 9

Prevent membrane freezing or becoming too fluid at high temps

Question 10

How does cholesterol work?

Answer 10

Forms H bond with carboxyl group on fatty acid chain
Reduces phospholipid packing which increases fluidity
Can also cause reduced phospholipid chain motion, reducing fluidity