lecture 2 membrane transport

Question 1

how does a g protein work

Answer 1

has a receptor that when something binds something happens in the cell

Question 2

macro transfer

Answer 2

large scale movement of molecules (endocytosis or exocytosis)

Question 3

micro transfer

Answer 3

smaller scale movement (cell membrane transport of small molecules and ions)

Question 4

clathrin are proteins that bind to membrane to help

Answer 4

endocytosis and exocytosis to open up the membrane

Question 5

can hydrophobic molecules pass the membrane

Answer 5

yes easily (O2, CO2 and N2 and steroid hormores)

Question 6

small uncharged polar molecules

Answer 6

can get through the membrane relatively easily (H20, Urea, glycerol)

Question 7

large polar molecules

Answer 7

struggle to get through (glucose and sucrose)

Question 8

ions

Answer 8

cants get through

Question 9

resting membrane potential is determined by

Answer 9

distribution of ions across the membrane (mostly due to sodium and potassium)

Question 10

non-excitable cells have a K+:Na+ permeability of

Answer 10

2:1

Question 11

how to measure ion channel protperties

Answer 11

voltage clamp or patch/current clamp

Question 12

voltage clamp

Answer 12

stab cell with fine electrode which applies a small amount of voltage
another electrode records the difference in currents
can record what happens to ion current

Question 13

current clamp

Answer 13

you apply current and record changes in voltage

Question 14

patch clamp

Answer 14

recording pipette isolates a patch of membrane on the cell surface
can also electrically clamp the potential across the patch to measure current flow through a single ion channel

Question 15

passive (simple) diffusion

Answer 15

directly through the lipid bilayer
obeys Fick’s law of diffusion e.g. O2 from alveoli to pulmonary capillaries

Question 16

uses protein membranes

Answer 16

facilitated diffusion: through pores, channels and carriers (uniports)
Active transport: energy required to transport across membrane
co-transporters (symporters): movement of a solute coupled to the movement of another down its concentration gradient
counter-transporters (antiporters): coupled movement of two or more solutes in opposite directions

Question 17

J=P*ΔC

Answer 17

flux= permeability x concentration difference

Question 18

P=Dk/x

Answer 18

P = permeability
D = diffusion coefficient
k = partition coefficient
x = distance

Question 19

3 types of transporters that facilitate diffusion

Answer 19

channels (non gated)
gated channels
unipoters

Question 20

non gated channels

Answer 20

porins in bacteria

Question 21

gated channels

Answer 21

ENaC
ion channels
modulated by voltage, ligand binding etc

Question 22

uniporters (carriers)

Answer 22

GLUT1,2 and 4