3.1 cont

Question 1

Transport proteins

Answer 1

-lower activation energy for solutes to go across membrane
-act as doors for proteins to go through membranes

Question 2

Passive Transport/facilitated diffusion

Answer 2

-solutes move WITH the gradient
-NO ENERGY REQUIRED
-ALL CHANNELS are passive transport

Question 3

Active Transport

Answer 3

-solutes move AGAINST the gradient
-REQUIRES ENERGY

Question 4

Aquaporins

Answer 4

-CHANNELS that diffuse water across membrane
-water can move IN OR OUT of cell

Question 5

Aquaporin structure

Answer 5

-6 membrane-spanning ALPHA helices
-NPA(Asn-Pro-Ala) motif: Asn bonds with water and reorients water molecules as they go through the channel
-aromatic/arginine filter-excludes other molecules
-Arg195- repels cations
-His 180 is a bottleneck

Question 6

Ion channels

Answer 6

-ions rapidly move across membrane
-can go in or out
-can move more than 1 ion can pass at the same time
-ion selectivity is based on charge and size
-passive transport

Question 7

3 hallmark characteristics of ion channels

Answer 7

1. Ions move very fast
2. NOT saturable
3. Regulated/gated by membrane potential/binding to ligands

Question 8

Saturable vs not saturable

Answer 8

Ions: as the # of solute molecules increase so does the rate of transport–>straight slope line on graph
Transporter: Once max transport has been reached it will not go faster–>curve line on graph

Question 9

What structural features do Potassium channels have to transport K+ ions?

Answer 9

-Carbonyl cage: oxygen atoms form a cage that perfectly fits K+
-Size of carbonyl cage fits 4 K+ ions only
-helical dipole: along the length of channel helps stabilizes the positive charges

Question 10

How do voltage-gating of potassium channels work?

Answer 10

-Normally membrane is negatively charged
-Action potential causes Na+ ion channels to open, Na+ ions rush in and turn the membrane positive
-this causes voltage-gated K+ ion channels to open, K+ floods out and turns membrane negative again

Question 11

S4 helix

Answer 11

-voltage sensing helix (+)
-S4 close to inner face (membrane is - ) = potassium channel is CLOSED
-S4 pulled toward outside of cell (membrane is +)= potassium channel is OPEN

Question 12

4 differences between Ion channels and Ion Transporters

Answer 12

1. Transporters have a higher degree of substrate specificity
2. Transporters can transport substrates with and against their gradient
3. Transporters are kinetically saturable
   4.Transporters are double gated only 1 solute molecule can pass in a specific direction at a time, while ion has 1 gate and many ions can pass though and go either direction

Question 13

What does a depolarized membrane mean?

Answer 13

Membrane goes from negative to positive