1. NASA scientists are investigating a newly discovered life form: a single-cell
ID: 3475849 • Letter: 1
Question
1. NASA scientists are investigating a newly discovered life form: a single-celled organism found in the swampy canals. You have been contracted to perform an electrophysiology study. Using intracellular electrodes to measure the electrical charge inside the cell, you find it has a resting membrane potential of -45 mV when the outside fluid is arbitrarily set to 0 mV. Additionally, you have determined ion concentrations and listed them below.
Ion
Cell
[ ] in mOsm/L
Swamp
[ ] in mOsm/L
K+
5
150
Na+
15
175
Cl-
40
40
You have used new molecular biology techniques to insert protein channels into the cell membrane that allow only and to pass.
a. Predict which ion(s) will move.
b. Tell what direction it (they) will move and what force(s) is/are acting on it (them).
c. Calculate the equilibrium potential for K+, Na+, Cl-
d. Is the equilibrium potential for the same as the membrane potential? Why or why not?
e. What is the resting membrane potential of the single celled organism with these ionic conditions?
Ion
Cell
[ ] in mOsm/L
Swamp
[ ] in mOsm/L
K+
5
150
Na+
15
175
Cl-
40
40
Explanation / Answer
a - ans- Na+ ion
b ans-the Na+ will move into the cell because it showing the both chemical and electrical gradients.
c ans-equilibrium potentia calculated by Nernst equation
Eion = 61mV/z log [ion]out/[ion]in
Ek+ = 61 log 150/5 = +90.1mV
ENa+= 61 log 175/15 = +65.08 mV
E- = l-61 log 40/40 = 0 mV
d ans-No, Typical membrane potential for cells (resting potential) = -65 to -85 mV
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