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36 Cards in this Set
- Front
- Back
Order the following by how readily they cross the plasma membrane Na+, K+, Cl-, H2O, Urea/Glycerol |
CH20 > Urea/Glycerol > Cl- > K+ > Na+
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What distinguishes a channel from a carrier protein? |
Channels do not change conformation like carriers do |
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How do we measure free energy change for transport of an uncharged species across a membrane? |
Delta G = RT ln(C2/C1) |
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What R and T values do we use in measuring the free change of energy in transporting a species across a membrane? |
R = 8.315E-3 kJ/mol*K T = temp in kelvin |
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Where does the energy required for active transport come form? |
ATP or concentration gradients |
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How do we measure free energy change for transport of a charged species across a membrane? |
Delta G = RT ln(C2/C1) + ZF (delta V) Z = charge F = Faraday constant = 96.5 kJ/V*mol |
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How do we mathematically determine membrane potential? |
Nernst Equation Equilibrium Voltage = -(RT/zF) * ln(C_in/C_out) |
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What is the equilibrium voltage? |
The potential across a membrane when the driving force due to a concentration gradient = electrostatic forces that resist motion along the concentration gradient |
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How does a neurons membrane change in permeability during depolarization? |
Depolarization leads to an increase in sodium permeability followed by a spontaneous decrease in sodium permeability and increase in potassium permeability |
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How does a neuron return to resting potential? |
Once the membrane has spontaneously becomes less permeable to sodium and more permeable to potassium |
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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? |
The high pressure suction leads to a gigaohm seal |
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What happens to the hydration shell of an ion passing through a channel and where do we get the energy to do this? |
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 |
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How does a potassium channel exclude sodium? |
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 |
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How does potassium contribute to the selectivity filter? |
At low potassium concentrations, the filter collapses in on itself |
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What is the 1,3 or 2,4 configuration of the ion channel? Why does this occur |
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 |
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How does the selectivity filter of a chloride channel differ form that of a potassium channel? |
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 |
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Describe the conformational change that occurs in ion channel gating? |
The channel changes from V (closed) like to a cylinder |
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How do voltage gating ion channels change between their open and closed conformation? |
A change in membrane potential pulled transmembrane "paddles" into position depending on voltage |
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What feature of voltage-gated transmembrane "paddles" primary sequence contributes to their ability to change conformation? |
Multiple positively charged AA side chains that move in and out of the membrane |
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How would trypsin inactive a sodium/potassium channel? |
It would trim the channels' first 20 residues which are the ball and keep it persistently open |
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How do we inactivate a channel according to the ball and chain model? |
The "ball" domain is a large tether cation that gets pulled into the channels once it's open blocking further ion conduction |
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How would modifying the "chain" length in the ball-and-chain model effect inactivation? |
Shortening the chain would increase inactivation rate by making the ball easier to find its target |
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What about the amino acid sequence of the helices lining the acetylcholine receptor may contribute to the conformational changes seen in opening and closing? |
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 |
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How can we measure transport through membranes? |
separate 2 chambers by glass which is sealed with a membrane that you want to study |
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How do we form a protein translocating channel? |
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 |
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How does the Aromatic Arginine (ar/R) selectivity filter allow water to pass through aquaporins? |
The ar/R filter strips hydrogen bonds from water allowing single molecules to be detached from bulk water for transport |
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What is the importance of lining aquaporins with positively charged residues? |
It prevents the transport of protons and so they will not disrupt proton gradients |
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What type of transporter is lactose permease and why? |
Secondary active symptorter Because it couples a proton gradient and transports both protons and lactose in the same direction |
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What's the difference between a primary and secondary active transporter? |
Secondary transporters couple to the energy of other molecules rather then getting their own via ATP hydrolysis or something |
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What are the steps in the lactose permease stmport mechanism? |
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
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What is a P-type ATPase? Give examples from lecture |
A unidirectional pump that couples phosphorylation and conformation changes
SERCA Na+ K+ ATPase |
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What role does calcium play in the SERCA calcium pump conformation? |
With calcium, the N (ATP nucleotide) binding domain and P (phosphoryl-acceptor) domains are occluded and inaccessible |
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What is the mechanism of calcium transport via SERCA? |
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 |
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Describe how the Na+ K+ pump works |
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 |
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What contributes to the large free energy change of ATP hydrolysis? |
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 |
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How does hydration contribute to ATP hydrolysis? |
ADP and Phosphate can bind more water than ATP can |