Test 2 Ch. 13 Membrane Transport

Front 1

Order the following by how readily they cross the plasma membrane

Na+, K+, Cl-, H2O, Urea/Glycerol

Back 1

CH20 > Urea/Glycerol > Cl- > K+ > Na+

Front 2

What distinguishes a channel from a carrier protein?

Back 2

Channels do not change conformation like carriers do

Front 3

How do we measure free energy change for transport of an uncharged species across a membrane?

Back 3

Delta G = RT ln(C2/C1)

Front 4

What R and T values do we use in measuring the free change of energy in transporting a species across a membrane?

Back 4

R = 8.315E-3 kJ/mol*K

T = temp in kelvin

Front 5

Where does the energy required for active transport come form?

Back 5

ATP or concentration gradients

Front 6

How do we measure free energy change for transport of a charged species across a membrane?

Back 6

Delta G = RT ln(C2/C1) + ZF (delta V)

Z = charge

F = Faraday constant = 96.5 kJ/V*mol

Front 7

How do we mathematically determine membrane potential?

Back 7

Nernst Equation

Equilibrium Voltage = -(RT/zF) * ln(C_in/C_out)

Front 8

What is the equilibrium voltage?

Back 8

The potential across a membrane when the driving force due to a concentration gradient = electrostatic forces that resist motion along the concentration gradient

Front 9

How does a neurons membrane change in permeability during depolarization?

Back 9

Depolarization leads to an increase in sodium permeability followed by a spontaneous decrease in sodium permeability and increase in potassium permeability

Front 10

How does a neuron return to resting potential?

Back 10

Once the membrane has spontaneously becomes less permeable to sodium and more permeable to potassium

Front 11

How does patch-clamp ensure that the current flowing through the pipette is identical to the current flowing through the membrane covered by the pipette?

Back 11

The high pressure suction leads to a gigaohm seal

Front 12

What happens to the hydration shell of an ion passing through a channel and where do we get the energy to do this?

Back 12

The hydration shell gets stripped once it's about 2/3 of the way into the pore. The hydration shell interactions are replaced with peptide backbone interactions where the carbonyls are directed into the channel

Front 13

How does a potassium channel exclude sodium?

Back 13

The radius of sodium is too fall for it to fully interact with the carbonyls thus making it energetically unfavorable to shed it's hydration shell

Front 14

How does potassium contribute to the selectivity filter?

Back 14

At low potassium concentrations, the filter collapses in on itself

Front 15

What is the 1,3 or 2,4 configuration of the ion channel? Why does this occur

Back 15

In potassium transport events, electrostatic repulsion prevent potassium from coming too close. So at any given point in the selectivity filter, a potassium ion can only be in the 1,3 or 2,4 configuration interspersed with water at the other sites

Front 16

How does the selectivity filter of a chloride channel differ form that of a potassium channel?

Back 16

In K+ channels, the C-terminal of the helices are coordinated with carbonyls on the backbone while Cl- channels have their N-termini amino groups coordinated towards the anion

Front 17

Describe the conformational change that occurs in ion channel gating?

Back 17

The channel changes from V (closed) like to a cylinder

Front 18

How do voltage gating ion channels change between their open and closed conformation?

Back 18

A change in membrane potential pulled transmembrane "paddles" into position depending on voltage

Front 19

What feature of voltage-gated transmembrane "paddles" primary sequence contributes to their ability to change conformation?

Back 19

Multiple positively charged AA side chains that move in and out of the membrane

Front 20

How would trypsin inactive a sodium/potassium channel?

Back 20

It would trim the channels' first 20 residues which are the ball and keep it persistently open

Front 21

How do we inactivate a channel according to the ball and chain model?

Back 21

The "ball" domain is a large tether cation that gets pulled into the channels once it's open blocking further ion conduction

Front 22

How would modifying the "chain" length in the ball-and-chain model effect inactivation?

Back 22

Shortening the chain would increase inactivation rate by making the ball easier to find its target

Front 23

What about the amino acid sequence of the helices lining the acetylcholine receptor may contribute to the conformational changes seen in opening and closing?

Back 23

AA sequence suggests alternating small polar/neutral and large nonpolar region

In the closed state, the large nonpolar residues might form a closed hydrophobic ring occluding the pore

Front 24

How can we measure transport through membranes?

Back 24

separate 2 chambers by glass which is sealed with a membrane that you want to study

Front 25

How do we form a protein translocating channel?

Back 25

Form a bacterial protoplast that has specific protein receptors on its surface

The membrane of the protoplast fuses with the pure membrane covering the pore between chambers

Measure voltage changes upon addition of a single peptide

Front 26

How does the Aromatic Arginine (ar/R) selectivity filter allow water to pass through aquaporins?

Back 26

The ar/R filter strips hydrogen bonds from water allowing single molecules to be detached from bulk water for transport

Front 27

What is the importance of lining aquaporins with positively charged residues?

Back 27

It prevents the transport of protons and so they will not disrupt proton gradients

Front 28

What type of transporter is lactose permease and why?

Back 28

Secondary active symptorter

Because it couples a proton gradient and transports both protons and lactose in the same direction

Front 29

What's the difference between a primary and secondary active transporter?

Back 29

Secondary transporters couple to the energy of other molecules rather then getting their own via ATP hydrolysis or something

Front 30

What are the steps in the lactose permease stmport mechanism?

Back 30

1) Outside proton binds to COO- in permease

2) In it's COOH form, permease can bind lactose

3) Structure everts opening inside the cell

4) Permease unbinds inside the cell

5) Proton unbinds inside the cell

6) Final eversion opening to extracellular side

Front 31

What is a P-type ATPase? Give examples from lecture

Back 31

A unidirectional pump that couples phosphorylation and conformation changes

SERCA

Na+ K+ ATPase

Front 32

What role does calcium play in the SERCA calcium pump conformation?

Back 32

With calcium, the N (ATP nucleotide) binding domain and P (phosphoryl-acceptor) domains are occluded and inaccessible

Front 33

What is the mechanism of calcium transport via SERCA?

Back 33

1) 2 Ca2+ binds from the cytoplasmic side

2) Calcium bound SERCA (E1 state) accepts an ATP from the cytoplasmic side in it's N domain

3) The ATP phosphorylates Asp 351 in the P Domain

4) ADP and calcium is released to interior of SR (E2 state)

5) Phosphorylaspartate is hydrolyzed

6) Pi release causes collapse of E2 state and eversion to E1

Front 34

Describe how the Na+ K+ pump works

Back 34

3 Na+ bind to intracellular portion of unphosphorylated pump

Upon phosphorylation, eversion releases Na+ to outside of cell

Eversion allows for binding of 2 K+

ATP hydrolysis causes eversion and release of K+ into cell interio

Front 35

What contributes to the large free energy change of ATP hydrolysis?

Back 35

1) Reduction of electrostatic repulsion

2) Stabilization due to hydration

3) Resonance stabilization of ADP and phosphate

4) Le Chatlier's principle, there is more ATP than ADP at physiological conditions

Front 36

How does hydration contribute to ATP hydrolysis?

Back 36

ADP and Phosphate can bind more water than ATP can