C/P AAMC fl 3

ellieacevedo
Posts: 7
Joined: Tue Mar 06, 2018 12:30 pm

C/P AAMC fl 3

Postby ellieacevedo » Sat Apr 14, 2018 5:22 pm

I didn't realize I would have so many questions haha so I am going to write them all here :

#20 . when , if ever , would A or D be true ?

26 : was I supposed to know that monosodium is more acidic than disodium ? not sure I understand this answer choice.

29 : I chose B because it said it wanted the NONproductive reaction which the passage said was the H202 production? I know I thought about picking A as well but I thought it was missing FAD!? So , i assumed they only wanted H202 equation. Why is FAD not included in A?

31. I chose A , I can't figure out what this graph is saying. If the line is higher, it hydroxylates more and produces h202 less?

32. Doesn't FAD also undergo reduction? Does net reduction always mean the last one to be reduced?

35: why not D?

42. Could you please elaborate on the relationships between ph/pka/ uncooperativity ? I chose A so I think I am missing something!

thank you so much! this is my last practice test so I want to make sure I really know the mistakes I'm making !
NS_Tutor_Andrew
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Posts: 520
Joined: Mon May 23, 2016 1:47 pm

Re: C/P AAMC fl 3

Postby NS_Tutor_Andrew » Mon Apr 16, 2018 3:37 pm

Hi ellie,

No problem! Let me take them one by one.

ellieacevedo wrote:I didn't realize I would have so many questions haha so I am going to write them all here :

#20 . when , if ever , would A or D be true ?


Do you mean A and C, which could occur in non-uniform electric fields? Essentially there's an infinite variety of non-uniform electric fields that could generate any number of patterns. This page has some examples under the heading of "unequal charges" that give some examples of what that could look like. In general, unequal charges or many charges with asymmetric placement could lead to this.

26 : was I supposed to know that monosodium is more acidic than disodium ? not sure I understand this answer choice.


They're asking you to recognize that monosodium phosphate would yield H2PO4- while disodium phosphate would yield HPO4(2-), and to combine that with the pKa values given for phosphoric acid to recognize that H2PO4 has a pKa of 7.2 and would be the perfect candidate to get that pH down to 7.2. Definitely tricky! But the only outside knowledge you need is to recognize the chemical formulas and what pKa implies.

29 : I chose B because it said it wanted the NONproductive reaction which the passage said was the H202 production? I know I thought about picking A as well but I thought it was missing FAD!? So , i assumed they only wanted H202 equation. Why is FAD not included in A?


This is also definitely a tough question. You're very much right that you need H2O2 as a product. The idea seems that they want the entire reaction including the nonproductive step, or "the first step" from the passage plus the "nonproductive" step. This means that NADPH --> NADP+ needs to be included. FAD is a reactant in the first step, but it is regenerated by FADH-OOH > FAD + H2O2, so it's not included in the net reaction. Hope this helps clarify that question!!

31. I chose A , I can't figure out what this graph is saying. If the line is higher, it hydroxylates more and produces h202 less?


Basically, the Y-axis is a measure of how fast the second step of the reaction is going. Higher values mean a faster reaction, and the different lines are different substrates (a key piece of info is that the passage tells you that H2O2 is produced if anything but Compound 1 is present in the active site). Thus, the question leads you to compare the black dots for Compound 1 with the black squares for lysine at pH 7.5 and calculate the ratio of kcat. I hope this answers your question! The key idea is that kcat is a measure of rate.

32. Doesn't FAD also undergo reduction? Does net reduction always mean the last one to be reduced?


The idea is that FAD is reduced to FADH, but then FADH is oxidized to FAD. Because FAD is reduced and then regenerated, it undergoes no net reduction. Instead, it works as a cofactor (think "catalyst" -- it helps the reaction go, but is neither consumed nor produced overall). Phew, what a passage!

35: why not D?


In a nutshell, the passage tells you that HRP oxidizes phenols, so that's where you'd expect the radical to form. I can see some ways in which the wording could be interpreted in another way, but as a rule of thumb, it's best to go for the most straightforward interpretation (i.e., it tells you that it oxidizes phenols and that the oxidation takes place on the ring substituent, so the -OH group of a phenol would be the best way to combine those statements).

42. Could you please elaborate on the relationships between ph/pka/ uncooperativity ? I chose A so I think I am missing something!


For this question, it's important to keep in mind that it's not asking you for much outside knowledge, besides knowing that sharp S-shaped curves are characteristic of high levels of cooperativity. The question is not asking about pKa, it's asking about "pK" (the missing "a" matters), which the explanation defines as "the pH at which the fraction of folded DNA is 0.5". This isn't really common knowledge, so I think you're basically asked to guess that pK is the pH at which 50% of something happens, so you're looking for 0.5 on the y-axis. So the thought process is to recognize that the sharp S-shape in the 5hmC-WT curve means that it has the highest unfolding cooperativity, and then use a reasonable guess about pK to infer that it must have a low pK value b/c it declines at lower pH values than the other curves. Very tricky question that requires you to go out on a bit of a limb when interpreting the graph, which is usually not recommended.

thank you so much! this is my last practice test so I want to make sure I really know the mistakes I'm making !


You're very welcome, and best of luck!!
Andrew D.
Content Manager, Next Step Test Prep.

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