3. You\'ve synthesized different sets of lipid vesicles, which are small, spheri

Question

3. You've synthesized different sets of lipid vesicles, which are small, spherical phospholipid- bilayer enclosed structures with an aqueous interior. A. (6pts) Vesicles in Set A contain no membrane proteins and no solutes in the inside (just water). You put these vesicles into a solution containing 4 types of molecules: ammonia (NH3), nitrogen gas (N2), RNA & sorbitol sugar (CeH40e). You measure the concentration of each of the solutes inside samples of vesicles over time, and the plot shows the results. Which curve corresponds to each molecule? Time (4pts) Vesicles in Set B contain the potassium (K+) channel protein in their membranes. You can set the initial concentrations of K- ions inside and outside the vesicles. Under what initial conditions will you observe K flow into the vesicles?

Explanation / Answer

In order to interpret this experiment you must take into account the size of the molecules. In this case, the molecular nitrogen (N2) and the ammonium ion (NH3) would be the first to pass since they are the smallest molecules, and in the end the sorbitol and the RNA (Even this molecule being very large would not be able to enter the cell).

Now you can have confusion between nitrogen and ammonium which cross first. In this case the ammonium is the one that passes first since it is in an electrically neutral configuration, if it were the case that it was ionized (as ammonium ion NH4+) then the molecule could not cross the membranes of the liposomes.

For the second case you should remember how osmosis works. Always the molecules will flow from a gradient of greater concentration to one of lower concentration. The scenario in which potassium ions will flow into the liposome is one in which there is a low concentration of potassium ions in the liposome (or even that there is only water) and a higher concentration of ions postassium in the external environment. This trend will be maintained until the concentrations in both the internal and external environment are equalized.

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