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 phospholipio- 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 (NHs), nitrogen gas (N2), RNA & sorbitol sugar (CeH140s). 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 B. (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 conditions will you observe K+flow into the vesicles? outside the vesicles. Under what initial

Explanation / Answer

A. Set A containing no membrane proteins and water inside the vesicle will have the following order of the transport:
Gases like nitrogen and ammonia will passively diffuse across the membrane. Sorbitol, sugar alcohol, is a small uncharged polar molecule which can also pass through the membrane. RNA having negatively charged backbone will be repelled by the negatively charged phospholipid bilayer. Therefore,
i) nitrogen ii) ammonia iii) sorbitol iv) RNA

B. The concentration of potassium ions is generally higher inside the cells and lower outside. Channels specific to potassium ions open selectively to these ions based on the gating arginine molecules. The selectivity fiter is based on the TVGYG aminoacids.The ion conduction pathway is filled with oxygen atoms which provide four binding sites for K+ . When a K+ enters the selectivity filter, the outermost K+ ion enters the extracellular solution. Upon opening of the channels, conformational change in the voltage senosr domain will result in the transfer of 12-13 elementary charges across the field.

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