L6 - cell membranes

Question 1

what molecules is the lipid bilayer impermeable to

Answer 1

almost all water soluable
charged / polar molecules
large molecules

Question 2

what molecules is the lipid bilayer generally permeable to

Answer 2

small uncharged/Hphobic (lipid soluable) molecules

Question 3

what charge do transmembrane proteins often have

Answer 3

-ve

Question 4

define primary active transport and give an example

Answer 4

movement of molecules from a low to high concentration using energy from hydrolysis of ATP
NA/K ATPase pump

Question 5

define secondary active transport and give example

Answer 5

movement of molecules from a low to high concentration using electrochemical gradient of another molecule
NA / glucose co transporter

Question 6

what is facilitated diffusion and give an example

Answer 6

movement of a molecule down its conc gradient via a channel (GLUT)

Question 7

what does simple diffusion across the cell membrane depend on

Answer 7

conc gradient

Kow

Question 8

what is Kow

Answer 8

equilibrium constant for the partitioning of a molecule between oil + water

Question 9

what does a higher Kow indicate

Answer 9

more lipid soluable (Hphobic)

faster diffusion through bilayer

Question 10

list the types of gated channels

Answer 10

1. voltage gated
2. ligand gated (EC)
3. ligand gated (IC)
4. mechanically gated

Question 11

explain ATPase pump mechanism

Answer 11

1. Na binds to intracellular site which triggers autophosphorylation ATP - ADP+Pi+ energy
2. energy leads to conformational change releasing Na+ and exposing the K+ binding site
3. K+ binds triggering dephosphorylation
4. pump returns to original position and K discharged into cell

Question 12

what is J max

Answer 12

max rate of molecule uptake

Question 13

name the sodium glucose transporters and where are they found

Answer 13

SGLT 1 - intestinal epithelial cells (dietary glucose)

SGLT 2 - Epithelial cells in PT of kidney for reabsorption of glucose

Question 14

explain mechanism of Na / Glucose transporters

Answer 14

uses energy from Na gradient movement to drive the movement of glucose
[Na] kept low within the cell (maintaining gradient) by Na/K ATPase pump

Question 15

what are the names of the transporters that allow glucose facilitated diffusion

Answer 15

GLUT 1-12

Question 16

in the Na/K ATPase pump how much Na / K goes in / out

Answer 16

3Na in / 2K out

Question 17

• explain mechanism of cholera toxin *

Answer 17

1. CT binds to GMI ganglioside receptor on apical membrane of intestinal cells
2. endocytosis into cell, then CT transported through golgi to ER
3. in ER, CT subunits split α1 enters cytosol
4. a1 binds to and overactivates ‘heterotrimeric GTPase GSα’ which activates adenylyl cyclase to constantly produce cAMP
5. cAMP activates CFTR channel (Cl- channel) leading to large Cl- secretion
6. Na+ leaves following -ve gradient
7. water follows Na (osmotic gradient)

Question 18

what is a ligand gated ion channel

Answer 18

carrier protein that requires binding of ligand to trigger conformational change and open channel

Question 19

what is mechanical gate

Answer 19

carrier protein that relies on pressure to open

Question 20

by what mechanism do the SGLT transporters work

Answer 20

secondary active transport

Question 21

what effect does insulin have on GLUT4

Answer 21

results in translocation of GLUT4 to the plasma membrane