Membrane Proteins

Question 1

Evidence for proteins in membranes

Answer 1

Functional

• facilitated diffusion
• ion gradients
• specificity of cell responses

Biochemical

• Membrane fractionation and gel electrophoresis
• Freeze Fracture

Question 2

Mobility of proteins in bilayers

Answer 2

conformational change
rotational
lateral
NO FLIP FLOP

Question 3

What are the restrictions on protein mobility?

Answer 3

membrane protein associations
association with extra-membranous proteins
lipid mediated effects
proteins tend to separate out into the fluid phase or cholesterol poor regions

Question 4

PERIPHERAL PROTEINS

Answer 4

bound to surface
electrostatic and hydrogen bond interactions
removed by changed in pH or in ionic strength

Question 5

Integral proteins

Answer 5

• Interact extensively with hydrophobic domains of the lipid bilayer
• cannot be removed by manipulation of pH and ionic strength
• are removed by agents that compete for non-polar interactions

Question 6

Properties of transmembranous polypeptide

Answer 6

R groups are largely hydrophobic

often alpha helical

Question 7

Hydropathy plot

Answer 7

take the amino acid sequence and go down it and figure out if it is hydrophobic or hydrophilic

regions that are hydrophobic are the parts that are in the transmembranous domain

Question 8

Protein topology

Answer 8

orientation of the protein in the bilayer

all proteins have a distinct and defined topology

Question 9

Association of proteins with bilayers

Answer 9

fatty acid modification an insert themselves into the membrane which makes the structure less random by restricting them

can be present on the extracellualr side or cytoplasmic side