membrane proteins

Question 1

evidence for proteins in the membrane

Answer 1

facilitated diffusion, ion gradients, cell response specificity swell as gel electrophoresis and freeze fracture

Question 2

how does SDS PAGE show proteins exist

Answer 2

SDS-PAGE with erythrocytes membrane proteins shows bands each representing different proteins

Question 3

how does freeze fracture show the existence of proteins

Answer 3

freeze the cell and then cut with a sharp knife then use the shadows to view the proteins through an electron microscope

Question 4

types of movement of proteins in the bilayer

Answer 4

rotational, lateral, conformational NO FLIP FLOP - too much energy required for this

Question 5

how can the movement of proteins in the bilayer be restricted

Answer 5

may be aggregated to one another preventing movement or tethered to substrate outside cells or interacting with other cells.

Question 6

the 2 types of membrane proteins

Answer 6

peripheral - on surface and bound by H bonds and removed by pH changes or ionic strength changes
integral interact with hydrophobic domains and cannot by the above methods and only by detergents which destroy the membrane

Question 7

what do hydropathy plots show

Answer 7

for each peak into the positive zone (orange) this shows the presence of proteins. if there are 7 proteins then there will be a GPCR which has 7 domains. negative area is blue

Question 8

what is membrane topology

Answer 8

may have other groups either side of the transmembrane helix (part between the bilayer) e.g sulphide groups or oligosacherides attached

Question 9

what is spectrin

Answer 9

erythrocytes must be very strong to prevent sheering moving through small gaps and spectrin has very strong coiled structure arranged in a lattice bound to transmembrane proteins in the membrane on the intracellular side. keeps membrane integrity

Question 10

what is spherocytosis

Answer 10

spectrin is depleted by 40-50% and therefore RBC are round and lyse easily releasing haemoglobin so can’t carry enough o2. need blood transfusion every 120 days

Question 11

what is elliptocytosis

Answer 11

defect in spectrin molecule where it can’t form heterotetramers and turn into rugby ball shapes. results in anaemia and lysis of some cells

Question 12

how do we synthesise a protein into membrane or organelle

Answer 12

use SRP to prevent translation and attach I to receptors on organelle and then its translated there. either cut and falls through into lumen or hydrophobic interactions hold it in membrane. DRAW out full version