AAMC FL 2 B/B #19 question?

[br2pi5]

Hi guys! I got this question wrong because I associated aqueous solution with having oxygen present? The passage says that the protein is only detected under anaerobic conditions (no oxygen). Therefore I thought roman number I was wrong since in aqueous solution the protein wouldn't be detected. I feel I thought way too much about this and made the question more complex than it needed to be, thoughts?

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[anyusernamenottaken]

is there anymore info in the passage? and aqueous solutions would just have to be polar, not necessarily due to O2

 

[NextStepTutor_1]

Hi @br2pi5 -

Yes, as @anyusernamenottaken pointed out, aqueous solutions can be anaerobic or aerobic. All it means for a solution to be aqueous is that it has solutes dissolved in H2O -- it tells us nothing about the presence of dissolved gases.

For this Q, you want to go to Fig. 2 and the paragraph above it. We're told that the fluorescent molecule ANS shows fluorescence when it binds to the hydrophobic surface residues of proteins, and Fig. 2 shows us that adding DPC, a detergent (the dotted line), greatly increases the amount of fluorescence compared to aqueous solution (the bottom two lines). These two observations imply that most of the surface-facing residues are hydrophilic in aqueous solution, but adding detergent changes the conformation of the protein such that hydrophobic residues are displayed at the surface. This gets us RNs I and III.

Hope this helps, & best of luck!

 

[br2pi5]

Hi @br2pi5 -

Yes, as @anyusernamenottaken pointed out, aqueous solutions can be anaerobic or aerobic. All it means for a solution to be aqueous is that it has solutes dissolved in H2O -- it tells us nothing about the presence of dissolved gases.

For this Q, you want to go to Fig. 2 and the paragraph above it. We're told that the fluorescent molecule ANS shows fluorescence when it binds to the hydrophobic surface residues of proteins, and Fig. 2 shows us that adding DPC, a detergent (the dotted line), greatly increases the amount of fluorescence compared to aqueous solution (the bottom two lines). These two observations imply that most of the surface-facing residues are hydrophilic in aqueous solution, but adding detergent changes the conformation of the protein such that hydrophobic residues are displayed at the surface. This gets us RNs I and III.

Hope this helps, & best of luck!

Got it, for some reason I thought having H2O could tell us about O2 but I was wrong, thank you for your explanation and for always being so helpful!

 

[NextStepTutor_1]

Hi @br2pi5 -

Of course! Glad to help 🙂. Water can be electrolyzed to H2 and O2, but it's not a spontaneous process -- I don't know the equilibrium constant off the top of my head, but it's tiny, so you would expect water to generate truly negligible amounts of O2 by itself, without the application of an electric current. For all intents and purposes, water can definitely be anaerobic. However, water does dissociate (in very small, but somewhat more significant, quantities) into H+ and OH-. This is referred to as the autoionization of water, and its equilibrium constant (Kw) is [H+][OH-] = 10^-14 at 25°C, which is an important fact for acid-base chemistry. I wonder if these facts might have helped create this misperception? In any case, good luck as you keep studying!