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AAMC Sample
Moiz_6047
#1 Posted : Thursday, July 22, 2021 6:42:04 PM
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Question 8) I understand that you need to use velocity (100m/s) x time (ms) to find distance. My question is why a time of 1 msec? I was thinking maybe 2msec because that is when we see a voltage change occur from -70mv to +40mv.

Question 16) For disaccharides/polysaccharides to be a reducing sugar does only one monosaccharide need to contain a hemi-acetal group for the entire compound to be considered reducing or not a reducing sugar?

Question 27) Does ultrasound always use dopplers? Are there any others we should be aware of? Why is option C incorrect? I thought for the dopplers equation you would need for both the source and the object "feeling the frequency"?

Question 28) Why is the answer not D? For option C, how is hydrogen bonding possible as the other group 7a elements are not FON? I thought hydrogen was only when H bonded the FON, and the rest of the elements bonded to hydrogen was just a polar bond?

Question 32) I understand that in table 1 warfarin "competes" a higher degree to the binding site than Ibuprofen. How can we therefore deduce that because there is more "competition" CPFX will primarily bind here? Also is high Ka greater amount of product formed, and high Kd greater amount of reactant formed? I thought acid dissociation constant was Ka?

Question 38) Would really appreciate help here, really lost on the mechanism haha

Question 39) I understand that this is a intermolecular ester reaction, can we still form it between carboxylate and alcohol or does it need to be carboxylic acid?

Why is the NH not protonated as it is a base?
INSTR_Katrina_128
#2 Posted : Saturday, July 24, 2021 4:20:42 PM
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Q8: We can see that a "spike" occurs in the graph, and that takes place over a time of 1 millisecond (1 msec). This suggests that the probe has a resolution of 1 ms or 10^-3 s. Specifically, the event occurs when the SPIKE occurs in the graph.

If the pulse travels at 100 m/s or 10² m, then the closest distance we can place the electrodes can be found from

speed = distance / time

distancce = speed * time

distance = (10² m/s) * (10^-3 s) = 10^-1 m = 0.1 m

Therefore, B is the best answer.

Q16: Yes. Very good! Only one part of the di- or poly-saccharide needs to interconvert to the open-chain form for the sugar to be considered a reducing sugar.

Q27: Yes, the Doppler effect is the primary mechanism by which this test works because the test is trying to show the MOTION of the fetus. This is called Doppler ultrasound.

Based on the formula for the Doppler effect:

fobserved = fsource * (v +- vo)/(v -+ vs)

We need to have ONE UNKNOWN.

The best answer is B because it leaves us with one unknown. C is not a good answer because it leaves us with zero unknowns.

Q28: Yes, hydrogen bonding can only occur with FON atoms as you say. So H-bonding will occur between HF to a much greater degree (actually... AT ALL) than it would if we had H-Cl or H-Br because Cl and Br aren't one of the FON atoms. C is the best answer. D doesn't answer the question as well as C does.

Q32: We're used to seeing Ka mean acid dissociation constant, but in this passage, it doesn't mean that.

First (as defined in the passage) K0 is the affinity of CPFX to bind with BSA. Then, Ka is the affinity of (either) warfarin or ibuprofen to find with BSA.

We are told in the passage (above Table 1) that warfarin likes to bind to site I and ibuprofen likes to bind to site II.

Since Ka/K0 is 0.46 for warfarin, this suggests that there is a competition for binding to Site I when BOTH warfarin and CPFX are added together. In other words: 46% of the time, warfarin will bind to Site I, while 54% of the time, CPFX will bind to Site I.

We don't see as strong of a competition for Site II, because the Ka/K0 value is 0.87. In other words, 87% of the time, ibuprofen binds to Site II, and ONLY 13% of the time, CPFX binds to Site II.

Therefore, Site I is the preferential bonding location for CPFX, and C is the best answer.

Q38: This is a very very heavy OChem question. I've found a fully-drawn out mechanism for you:

https://i.imgur.com/1CTl7Ke.jpeg

The major thing that I noticed was that none of the marked carbons are on a CARBONYL carbon. This really helped me track them through the mechanism.

Q39: It's fine that this is a carboxylate anion. Technically it exists in resonance with the other carbonyl group, so it is relatively stable with the excess negative charge.

I'm not sure which question you're referring to with regards to NH.
Moiz_6047
#3 Posted : Monday, July 26, 2021 4:26:30 AM
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Thanks Katrina!

The last question is referring to 47. Also, for 32 how do you Ka is the affinity of (either) warfarin or ibuprofen to find with BSA and not CPFX/BSA in the presence of warfarin/ibuprofin?
INSTR_Calla_139
#4 Posted : Thursday, July 29, 2021 9:31:23 PM
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Hello Moiz,

47) the compound doesn't need to be protonated to be a base. The good news here is that you don't need to know this in order to get the question correct.

32) We know this because the note above table 1 clues us in "K0 represents the affinity constant of CPFX in the presence of BSA only" here this tells us that they accounted for the CPFX also, the fact that they all bind to specific sites clues us in. I wouldn't worry too much about it.
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