Biological Membranes

Question 1

Give 5 general functions of biological membranes

Answer 1

1. Continuous, highly selective permeability barrier
2. Control of the enclosed chemical environment
3. Communication
4. Recognition:
   - signalling molecules
   - adhesion proteins
   - immune surveillance
5. Signal generation in response to stimuli (electrical, chemical)

Question 2

Give functions of different regions of plasma membrane

Answer 2

Interaction with basement membrane 
Interaction with adjacent cells 
Absorption of body fluids 
Secretion 
Transport 
Synapses – nerve junctions 
Electrical signal conduction 
Changing shape may change the properties of a particular region

Question 3

Generally what is the dry weight of a membrane?

Answer 3

40% lipid
60% protein
1-10% carbohydrate

Question 4

Re membrane lipids hydrophilic or hydrophobic?

Answer 4

Both - they are amphipathic, i.e. Contain both a hydrophobic and hydrophilic region

Question 5

What is the general composition of a phospholipid?

Answer 5

Phosphate head group, glycerol, fatty acid tails

Question 6

Name 1 example of a phospholipid

Answer 6

Phosphatidylcholine

Question 7

Name examples of polar head groups

Answer 7

Choline, amine (e.g. Ethanolamine), AA (e.g. Serine), sugars

Inositol

Question 8

What is the length of a fatty acid chain?

Answer 8

C14-C24

16 and 18 most common

Question 9

What introduces a kink in the chain?

Answer 9

CIA double bond

Question 10

What is a glycolipid?

Answer 10

Sugar containing lipid

Question 11

What is a cerebroside?

Answer 11

Head group sugar monomer

Question 12

What is a ganglioside?

Answer 12

Head group ogliosaccharide (sugar multimers)

Question 13

What is a Micelle?

Answer 13

Sphere o lipid with hydrophilic heads pointing outwards tails pointing inwards

Question 14

Describe 4 methods of phospholipid motion

Answer 14

Flexion
Rotation
Lateral diffusion
Flip flop (rare)

Question 15

What is the influence of cis double bonds in bilayer structure?

Answer 15

Kinks in the chains which reduces phospholipid packing

Question 16

Describe the structure of cholesterol

Answer 16

Polar head group, rigid planar steroid ring structure, non-polar hydrocarbon chain

Question 17

What part of cholesterol binds to a phospholipid and where on the phospholipid does it bind?

Answer 17

Beta OH group on cholesterol binds to O (which is on C=O) on glycerol part of phospholipid

Question 18

Describe the paradoxical effects of cholesterol on a membrane

Answer 18

At low temperature it prevents crystalisation as it interferes with the packing of the phospholipids - prevents phospholipids from packing too closely together so they don’t crystallise

At high temperature it reduces movement of the membrane - attracts fatty acid tails bc hydrophobic - packs them tightly together to decrease fluidity

Paradoxical because it can work to increase or decrease fluidity