Mnr

Question 0

What is the composition of a membrane?

Answer 0

40% lipid
60% protein
1-10% carbohydrate

Hydrated structures: 20% of total weight is water

Question 1

Functions of biological membranes

Answer 1

1) Continuous highly selective permeability barrier
2) Control of the enclosed chemical environment
3) Communication
4) Recognition -signalling mol/adhesion pro/immune surveillance
5) Signal generation in response to stimuli elec/chem

Question 2

What’s an amphipathic molecule?

Answer 2

Contains both hydrophilic and hydrophobic moieties

E.g. Phospholipid

Question 3

What’s the composition of a phospholipid?

Answer 3

• 2 Fatty acid chains ( C14-24, mostly C16-18)
• Phosphate
• Polar head group (attached to phosphate)

Head groups: choline, amines, sugars, amino acids

Question 4

Possible head group of a phospholipid?

Answer 4

Choline
Amines e.g. Ethanolamine
Sugars e.g. Inositol
Amino acids e.g. Serine

Question 5

How does sphingomyelin differ from a phospholipid?

Answer 5

Not based on glycerol

Replaces phophocholine with glycolipid

Question 6

What is a glycolipid?

Answer 6

Sugar containing lipid

Question 7

What are the types of glycolipid?

Answer 7

Cerebroside - head group is a sugar monomer, simple

Ganglioside - head group is an oligosaccharide ( sugar multimer), complex

Question 8

What are the possible structures lipids form in water?

Answer 8

Lipid micelle

Lipid bilayer

Question 9

What do phospholipids/glycolipds form in water and how?

Answer 9

Lipid bilayer
Spontaneous formation
- VdW attractive forces between hydrophobic tails
- Stabilised by non-covalent forces
e.g electrostatic/H bonding between hydrophilic moieties & interaction between hydrophilic groups and water

Question 10

What are the 4 types of phospholipid movements?

Answer 10

Flexion - intra-chain motion e.g. Kink formation
Rotation
Lateral diffusion - in plane of bilayer
Flip-flop - movement of lipid molecules from one half of bilayer to other

Question 11

Benefit of unsaturated double bonds (cis formation) in fatty acid chains?

Answer 11

Disrupt (hexagonal) packing of phospholipid

Increases membrane fluidity

Question 12

What is the structure of cholesterol?

Answer 12

Polar hydrophilic head group
Rigid planar steroid ring structure
Non-polar hydrocarbon tail (flexible)

Question 13

Why do cells have 45% cholesterol?

Answer 13

Prevent islands of crystal forming
Abolish endothermic phase transition of phospholipid bilayer
Cholesterol stabilises the plasma membrane by hydrogen bonding to fatty acid chains

Question 14

Paradoxial effects of cholesterol in phospholipid bilayer?

Answer 14

Abolishes endothermic phase transition of phospholipid bilayers
Stabilises plasma membrane by H bonding to fatty acids
Reduces phospholipid packing - increases membrane fluidity (inc space between phos)
Reduces phospholipid chain motion - decreases membrane fluidity (reduced vibrational motion)