3. Biological Function Of Membranes - Proteins

Question 1

What are the functions of proteins in membranes?

Answer 1

Facilitated diffusion
Ion gradients
Specificity of cell responses

Question 2

What is the biochemical evidence for proteins in membranes?

Answer 2

Membrane fractionation and gel electrophoresis

Freeze fracture

Question 3

What is freeze fracture?

Answer 3

Separates the membrane

Shows organisation of proteins and phospholipids within the membrane

Question 4

How can proteins move within the bilayer?

Answer 4

Conformational change
Rotational
Lateral diffusion
No flip flop

Question 5

What are the restrictions of membrane protein mobility?

Answer 5

Lipid mediated effects (proteins spate out into fluid phase or cholesterol poor regions)
Membrane protein associations
Association with extra-membranous proteins e.g. cytoskeleton

Question 6

Describe peripheral membrane proteins

Answer 6

Bound to surface
Electrostatic and H bond interactions
Removed by changes in pH or ionic strength (salt wash)

Question 7

Describe integral membrane proteins

Answer 7

Interact with hydrophobic domains of lipid bilayer
Cannot be removed by manipulation of pH and ionic strength
Removed by agents that compete for non-polar interactions

Question 8

Describe transmembrane polypeptides

Answer 8

R groups of amino acid residues are largely hydrophobic

Often alpha helical

Question 9

Where are integral, transmembrane and peripheral proteins?

Answer 9

Integral: hydrophobic part is in membrane
Transmembrane: spans across entire membrane, hydrophobic part within membrane
Peripheral: not touching membrane, attaches to transmembrane proteins by interactions

Question 10

What is topology?

Answer 10

Orientation of membrane - location of -N and -C termini