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Unformatted text preview: transport both molecules to the same side of a membrane, while antiporters move
the two molecules to opposite sides of the membrane.
3. (a) It is known that capsaicin, the active ingredient in hot and spicy foods, increases
the permeability of sensory neuron plasma membranes to cations. You speculate that
there is a specific ion channel within these neurons that binds capsaicin and is responsible
for this increased permeability. In your lab, you have the ability to visualize the calcium
uptake of cells using fluorescence microscopy and a calcium sensitive dye. How would
you identify the capsaicin receptor?
Make a cDNA library from the sensory neurons, transfect pools of clones
(individual cDNAs in plasmids) into cells that do not have a capsaicin dependent ion
channel, and look for a specific pool that increases calcium uptake in cells. Then
iteratively subdivide the pool until a single clone is identified and sequence the gene.
(b) You successfully clone the capsaicin receptor and decide to study its properties as an
ion-channel using patch clamping.
(i) The resting membrane potential of an oocyte not treated with capsaicin is –65
milliVolts. The sodium concentration of the patch electrode is 90 mM, and you have
measured the intracellular sodium concentration to be 8mM. What is the ∆G for the
inward movement of sodium ions at 37˚C? Is the process thermodynamically favored?
∆Gc = RT * ln (Nain/Naout) ∆Gm = zFE ∆G = ∆Gc + ∆Gm
cal/(K*mol) R = 1.987 F = 2.3 10^4 cal/(V*mol)
∆G = zFE + RT ln (Nain/Naout)
∆G = (1) * (2.3E4 cal/V*mol) * (-0.065 V) + (1.987 cal/(K*mol) * (310 K) * (ln 8/90)
∆G = -1.495 + -1.49
∆G = -2.98 Because ∆G is negative the process is thermodynamically favored. (ii) When performing a single channel patch clamp of an oocyte expressing the receptor,
you add 1µM capsaicin to the media and measure a current of 3pA. How many sodium
ions does the capsaicin receptor let into the cell per second?
Ampere = Coul...
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This note was uploaded on 01/23/2012 for the course LSM lsm1301 taught by Professor Seow during the Spring '11 term at National University of Singapore.
- Spring '11