Membranes And Receptors

Question 0

Describe the membrane composition?

Answer 0

40% lipid
60% protein
1 to 10% carbohydrate
20% water

Question 1

What are the functions of the membrane bilayer?

Answer 1

Highly selective permeability barrier
control of chemical environment
Signal generation in response to stimuli
recognition: immune surveillance, adhesion proteins, signalling molecules
communication between cell and environment

Question 2

Define amphipathic.

Answer 2

Contains both hydrophilic and hydrophobic moieties

Question 3

What lipids are involved in the plasma membrane?

Answer 3

Phospholipids
plasmalogens
glycolipids
cholesterol

Question 4

What is sphingomyelin?

Answer 4

A plasmalogens which is a nonclassical phospholipid

Sphingomyelin is not based on glycerol however its confirmation resembles other phospholipids

Question 5

What is a cerebroside and a ganglioside?

Answer 5

Both glycolipids where the phosphocholine is replaced with sugar.
Cerebrosides have a sugar monomer head
Gangliosides have an oligosaccharide head

Question 6

What drives the formation of a bilayer in water?

Answer 6

In water and amphipathic structures for micelles and bilayers
This is spontaneous and driven by the van der waals forces between hydrophobic tails

Question 7

What forces stabilise the cooperative structure?

Answer 7

Electrostatic and hydrogen bonds between hydrophobic moieties

Hydrophilic interactions between hydrophobic groups and water

Question 8

What are the four movements of lipids in the bilayer?

Answer 8

Intrachain motion
fast axial rotation
Lateral diffusion
flip-flop

Question 9

What are the functions of membrane proteins?

Answer 9

Enzymes 
transporters 
pumps 
Ion channels 
receptors 
energy transducers

Question 10

What movements can membrane proteins do in the plasma membrane?

Answer 10

Confirmation change
Lateral diffusion
rotation

Question 11

Why can’t membrane proteins flip-flop?

Answer 11

Membrane proteins are large hydrophilic moieties and this would require large amounts of energy to pass through the hydrophobic bilayer

Question 12

What restraints are there on the mobility proteins in the bilayer?

Answer 12

Lipid mediated effects
Membrane protein Associations
Association with extra membranous proteins

Question 13

How are peripheral membrane proteins attached to the membrane surface?
How can they be removed?

Answer 13

Electrostatic and hydrogen bonds

Changes in pH or ionic strength

Question 14

How are integral membrane proteins attached to the membrane?

How can they be removed?

Answer 14

They interact extensively with the hydrophobic regions of the lipid bilayer
Agents that compete for non polar interactions with the bilayer e.g. detergent and organic solvents

Question 15

What is the functional evidence for membrane proteins?

What is the biochemical evidence?

Answer 15

Facilitated diffusion, Ion gradients, specificity of cell responses

Membrane fractionation and gel electrophoresis, freeze fracture

Question 16

Why are proteins asymmetrically orientated in the biological membrane?

Answer 16

It’s important for their function for example receptors for hydrophilic extracellular messengers must be directed towards the extracellular space.

Question 17

What causes membrane proteins to span the vesicle membrane rather than being contained within it during membrane Protein synthesis?

Answer 17

The recognition of a stop transfer signal during translation into the ER lumin holds the protein in position across the membrane whilst the rest of the protein is translated in the cytoplasm.

Question 18

Describe the stop transfer signal.

Answer 18

Highly hydrophobic region of polypeptide

Comprises of hydrophobic, small or polar uncharged amino acids

Question 19

Describe the erythrocyte cytoskeleton.

Answer 19

Spectrin and actin molecules attached to adapter proteins (ankyrin and Glycophorin) binding to band 3 and 4.1 proteins respectively

Question 20

How is the cytoskeleton related to haemolytic anaemia?

Answer 20

Without cytoskeleton red blood cells become rounded and are therefore lysed in the capillary beds

Question 21

Give two hereditary conditions leading to haemolytic Anaemia.

Answer 21

Hereditary spherocytosis (Spectrin depleted by 40 to 50%, Rounded cells, lysis)
Hereditary elliptocytosis (Spectrin can't form  heterotetramers, fragile elliptoid cells, lysis)