26 Jun NPB 104L You are studying the regulation of a proton transport molecule
Question
Name______________________________
TA _____________________________
NPB 104L Quiz 5
Multiple Choice
Identify the letter of the choice that best completes the statement or answers the question.(1 pt each)
____
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1. You are studying the regulation of a proton transport molecule in the outer mitochondrial membrane. Further,
you predict that a mystery compound, Y, leads to an increase in the number of proton transport molecules
embedded in this membrane. In order to set up an experiment to test this hypothesis what should you vary
and what should you measure?
a. vary sodium in the presence and absence of Y, measure transport activity
b. vary H+ in the presence and absence of Y, measure transport activity
c. vary Y in the presence and absence of H+, measure the number of transporters
d. vary the number of transporters, measure proton flux across the membrane
e. vary transport activity in the presence and absence of Y, measure H+ concentration in the
inter-membrane space
2. Which of the following is an invalid prediction based upon our model of oxidative phosphorylation?
a. A complete block of the electron transport chain at complex III will stop oxygen
consumption.
b. Insertion of a gradient driven proton carrier in the outer mitochondrial membrane would
lead to increased oxygen consumption.
c. Excess inorganic phosphate in the matrix will cause a leak of inorganic phosphate into the
inter membrane space where it will inhibit binding of protons to the ATP synthase
molecule.
d. Artificially increasing the H+ concentration in the inter membrane space should drive more
ATP production.
Short Answer
3. You are asked to investigate the affect of ADH on frog skin and are given the following information (see
table). You then proceed to put a piece of frog skin in an Ussing chamber and fill both sides with 100%
Ringers solution. Suspecting that ADH works by increasing the permeability of the apical membrane to Na+
you want to see if adding ADH will drive the activity of the pump by increasing availability of substrate. You
prepare to add a physiological concentration of ADH to the chamber facing the basolateral side of the
epithelium and set out to measure pump activity. You intend to compare the activity of the pump in the
presence and absence of ADH. What is wrong with the experiment as you’ve set it up? What would you do
differently? (2 pts)
%Na+ (apical)
2
5
10
20
50
100
Na+/K+ pump Velocity
20 2.1
35 1.3
48 0.8
52 3.0
58 2.5
59 1.5
1
Name______________________________
TA _____________________________
4. We know that the production of ATP must be varied in order to match demand and we saw that the P/O ratios
recorded in lab were consistently lower than the classic value calculated for succinate (2.5). List three
different sites in the mitochondrion where cellular regulation could affect the P/O ratio and state how each
effect would be mediated (these are regulatory mechanisms used by the cell – not artificial interventions like
adding a manufactured uncoupler!). Describe one biologically beneficial reason why P/O ratio’s might be
lower than 2.5. (2 pts)
1.
2.
3.
Why?
Long Answer
5. You run the following two experiments:
1) You vary the concentration of substance X in the solution bathing your test cells and measure the activity
of the Na+/K+ ATPase. You get the following data:
[X]
(mM)
1 x 10-3
3 x 10-3
10 x 10-3
30 x 10-3
100 x 10-3
Na+/K+ ATPase
Activity
11.2 +/- 0.03
17.7 +/- 0.07
21.2 +/- 0.05
25.3 +/- 0.03
29.1 +/- 0.06
2) You repeat exactly the same experiment with one difference: this experiment is run in the presence of
FCCP and get the following data:
With FCCP
[X]
(mM)
1 x 10-3
3 x 10-3
10 x 10-3
30 x 10-3
100 x 10-3
Na+/K+ ATPase
Activity
10.2 +/- 0.03
11.7 +/- 0.07
12.2 +/- 0.05
13.3 +/- 0.03
13.6 +/- 0.06
2
Name______________________________
TA _____________________________
A) What is the important consequence of exposing cells to FCCP as it pertains to Na+/K+ ATPase
activity? (1 pt)
B) State a hypothesis for which the first experiment would be run as a test of that hypothesis. (1 pt)
C) What do the results of the second experiment suggest to us about the mechanism of X’s action?
(1 pt)
6. In class we discussed current-voltage relations for sodium and potassium and I plotted the following data:
A) In order to describe ionic current we rearranged Ohm’s Law to get: INa = gNa(Vm-ENa). We
referred to the term inside the parentheses as the “driving force”. What two forces are accounted for
by this term and how is each accounted for? (1 pt)
B) Why is the slope of the sodium current line less steep than that of the potassium current line? (1
pt)
3
Name______________________________
TA _____________________________
C) Identify Point “A” on the graph. How is sodium current different to the left versus the right of
this point? Why? (1 pt)
D) Which is greater at the normal resting membrane potential, sodium current or potassium current
(put dots on the graph to indicate where you’re getting your answer)? Why is this so? How do the
magnitudes of these two currents relate to the stoichiometry of the sodium/potassium pump? (3 pts)
4
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